harmonic balancers

[fekbmax]

Whats preferred for a full race Fe and why ?
ATI ? TCI ? Innovators west ? Or any other dampers for a internally balanced engine. 

[Stangman]

Got shortblock done at survival and we installed a romac

[cjshaker]

The Romacs are nice pieces, but don't hold their finish very well and will rust. The ATI dampers are VERY nice and seem quite popular within race circles. Just remember that the timing marks are off and your pointer must be adjusted accordingly. I have no experience with the others.

[blykins]

ATI is up there....Romac is up there....I've even used the Powerbond SS on some higher hp stuff.  Take your pick.

[fekbmax]

I been useing ATI's but was just curious as to what you guys think.

[jayb]

I always use ATI balancers.  A heavier balancer is better for a larger stroke.

[thatdarncat]

I have an Innovators West and happy with it ( came with my current motor ). Very popular with the stock & super stock drag racers. Timing marks are in the right spot and Ford pulley bolted up. I talked to them at the PRI show, sounded like they are Ford guys at the shop.

[Stangman]

What is the reasoning with the heavier balancer for the long stroke you would almost think you would want it lighter so it would rev faster or are you looking for more power after it alredy gets goin

[jayb]

As I understand it a heavier harmonic balancer helps smooth out any tendencies towards vibration.  The longer the stroke, the more you will have that tendency, so a heavier balancer is better. 

[Autoholic]

Here is the engineering answer as to why you need a heavier harmonic balancer with a longer stroke: moment of inertia. The bigger your stoke, the larger your moment of inertia, requiring more damping in order to smooth out the power. Same goes for the flywheel.

[Stangman]

I guess I can see that I was thinking about those hit and miss motors the bigger the flywheel the more it could work or pump or whatever you were using it for that makes sense autoholic

[Autoholic]

If you want to increase the responsiveness of the engine, how quick it can rev, you need to decrease the moment of inertia. This is why a shorter stroke will rev higher. But the moment of inertia also takes into account your reciprocating mass, so making everything as light as possible helps as well, to increase the acceleration of the engine. How reliable the engine will be will take into account your valvetrain as well, making this as light as possible helps you keep revving higher, longer. At this point, your gearing will also come into play as to how quick your engine will accelerate. I should note that the moment of inertia for your drivetrain will come into play. Light weight transmission gears, differential and the rotating mass of your rims and tires. This is part of the reason why carbon fiber and magnesium rims are there, the lower weight helps make the vehicle accelerate faster due to the engine having to work less to move the rotating mass. Another reason for these rims is by having less weight on your unsprung weight, there will be less force behind suspension travel.

[blykins]

Watch about making generalities that only short stroke engines can rev....

I hear this statement frequently but it's not always the case.  A long stroke engine can turn some very high rpms and respond immediately with the right combination.   The rotating assembly weight as well as how much hp/tq the engine makes play a big role. 

There are mountain motor class engines (700-800 ci) with 5.750" strokes that can easily turn 8000 rpm and get there in an instant...

[Nightmist66]

In Autoholics defense, I believe he was just stating shorter strokes will rev "higher" than long strokes. No doubt there are some big cube motors that turn the rpm. The high revving "short stroke" is best explained by the formula and indy engines, 15-20k rpm

[Autoholic]

I never said a long stroke couldn't rev high. The fact of the matter though is that a shorter stroke will always be able to rev higher than a longer stroke, with everything else being equal. There is a good reason why you only see short stroke engines in Formula 1. No matter what you do to a long stroke engine, it will still have a higher moment of inertia and that will limit how high it can rev and how fast the engine will get there. Done properly, you could make a high revving long stroke engine but what you'll have to do to get there will end up proving the law of diminishing returns. At some point you need to question your intent for the motor. Do you want it to be high revving and make its power in the stratosphere or do you want it to be torque monster that makes its power down low? And to be clear, I would say anything at or under 8000 RPM is low as far as the spark ignition ICE goes, when you have engines in motorcycles and formula racing that rev 14,000 rpm and higher. Oh and this doesn't even touch on the topic of reliability when trying to make a long stroke engine run 8,000 rpm or how streetable such an engine would be. Not to mention how expensive it will be because you are forced to use expensive materials like titanium and high strength steels. A high revving, big stroke engine is built mainly for one purpose, drag racing and as such, it gets rebuilt regularly.

[blykins]

I completely understand what you're saying....just wanted to make sure you weren't buying into a lot of wives tales that get passed around the forums though....

I hear this quite often from customers...."Well, I'd rather have the 4.125" stroke instead of the 4.250" because the longer stroke engines just won't rev."  Horse poo-poo.   I think a lot of guys have seen truck engines with 150 hp, no compression, and 40 lb flywheels, and automatically make a correlation that it's a longer stroke, so it's lazy...

Jay could probably tell you about the response of some of his longer stroke SOHC and wedge engines....they are not slouches. 

[turbohunter]

I understand inertia but I've never heard of "moment of inertia".
Would that be defined (in an internal combustion engine) as the "moment" the piston hits TDC and reverses course?
And if that is so, how does detonation play into (I assume) reducing (?) inertia?
Also since there are 7 other piston/rod/crank combos going through the same thing, is there a "moment"?
I'm guessing this is part of the reason why Brent cautioned about being general.

[blykins]

Inertia is a straight-line measurement... think of when you're driving in your car and you tap your brakes....your body wants to continue in the same direction it was headed. 

The moment of inertia is not really a time based unit, but it's a measurement of an objects resistance to changing rotational motion.  In physics/engineering, a moment is a tangential force which makes a torque. 

So in a rotating assembly, the crankshaft would have a moment of inertia, which would affect its ability to accelerate or decelerate quickly. 

What many people leave out when thinking of rotating assemblies and their abilities to accelerate/decelerate quickly is the amount of force acting upon them.  If you think of a figure skater, when she draws her arms and legs in close to her body, she rotates quicker.  That's what most people think of.  However, when you add a tangential force to that figure skater, you could essentially make her buzz up even with her arms and legs spread out a little. 

That's what I was referring to when I was talking about making general statements.  There are lots of variables in how quickly a rotating assembly can accelerate or decelerate.

Now, my caveat is that I'm a degreed Mechanical Engineer, but it's been 13-14 years since I've had to crack a physics/statics/dynamics book....so I'm probably a little rusty.

[fekbmax]

Easy fellas, lol.
So I'm running a kinda odd ball stroke/rod combo I guess. I suppose it would be a medium stroke. I do use a 4.125 steel crank and I'm using a 6.535 aluminum rod with venolia 4.140 pistons. Would I still benefit from a heavier balancer ?

[blykins]

Yes. 

If you're doing nothing but drag racing, I would aim for an ATI.

[cjshaker]

However, when you add a tangential force to that figure skater, you could essentially make her buzz up even with her arms and legs spread out a little. 

I want to hear more about THIS

[jayb]

Reading through this I have a few comments, and can offer a little more insight on moment of inertia.

First, it is not correct to simply say that an engine with a higher moment of inertia will accelerate more slowly than an engine with a lower moment of inertia.  It would be correct to say that at a specified horsepower level, an engine with a higher moment of inertia will accelerate more slowly.

Second, I think it is true that a longer stroke engine will not be able to rev as high as a shorter stroke engine.  At some point, right around 6300 feet per minute for piston speed, you hit a number where you just can't spin it any higher without damaging parts.  The longer the stroke, the higher the piston speed at any given RPM, so you can always RPM higher with a smaller stroke, given equivalent components.

My big SOHC engine revs faster than any engine I have ever had, and it is 585 cubic inches.  I'd never turn it past about 7800 RPM, but it gets there way, way faster than any other engine I've ever had.  Saying that a big engine won't rev fast is just flat wrong; you can rev really fast with lots of power, no matter what the moment of inertia is.  BTW, piston speed at 7800 for my 585" SOHC (4.6" stroke) is 5980 feet per minute.  That's as close as I ever want to get to the limit.  A super stock 427 FE can rev to 9500 RPM, and it will have the same piston speed as my big SOHC.

One other comment is that I don't think it is precise to say that moment of inertia is why you need a heavier harmonic balancer.  If the engine is a perfectly balanced flat plane engine, I don't think that a heavier harmonic balancer would help with a larger stroke, even with a higher moment of inertia.  Because FEs are V8 engines, there are some balance harmonics that can't be totally balanced out, and the heavier harmonic balancer helps to dampen the vibrations caused by those harmonics.  So I think that it is more a compensation for the basic layout of a V8 engine than strictly a function of moment of inertia.

A moment of inertia calculation basically takes the mass of a reciprocating component, and then multiplies that mass by the distance from the center of rotation to the center of gravity of the component.  So, taking a crankpin as an example, if you knew the weight of the crankpin, you could then assume that the center of the crankpin was its center of gravity, and multiply its weight by the distance from the center of rotation to the center of the crankpin.  This is just half the stroke.  You would then have to do this for all the crankpins, all the crankshaft counterweights, each connecting rod and piston, plus the harmonic balancer, flywheel, and any other reciprocating components. 

I took a stab at this once with a spreadsheet, reprinted below.  A lot of the stuff is a guess, because I just wanted to get an idea of how the moment of inertia affected the power production of the engine.  The units are kind of bizarre in the English system, slug-feet (!).  In the metric system it is kilogram-meters.  Inches are all converted to feet by dividing by 12, and pounds are all converted to slugs by dividing by 32.2 ft/second squared.  At the bottom of the third sheet is the calculated result, which tells you how much torque is required to accelerate the engine at a certain rate.

Just a little food for thought, fellas...   

[Autoholic]

Jay, I'm sorry but I have to disagree with you on this part... "It would be correct to say that at a specified horsepower level, an engine with a higher moment of inertia will accelerate more slowly."

If everything is equal except for the stroke, the longer stroke will accelerate slower than the shorter stroke. It's apples to oranges once you try and say this engine accelerated faster than this other engine even though it had a longer stroke AS WELL AS a bunch of other differences. With everything being equal, there is no way that the longer stroke can physically match the acceleration and rpm level of the shorter stroke. It doesn't matter what horsepower or torque is being made, it comes down to a shorter distance for the piston to travel. Shorter the distance, the quicker the piston will go from A to B. In reality it's damn near impossible to have everything equal except for the stroke BUT if you did do this, you would find that the shorter stroke engine made its peak power higher in the RPM band than the longer stroke. You would also find that the shorter stroke accelerated quicker. It has nothing to do with how much power is being made, this boils down to introductory physics.

Now if we were to build 2 engines that were very different, 1 with a long stroke and 1 with a short stroke and made sure that they were balanced as much as humanly possible. Both made to rev as high as they possibly can. Longer stroke has the higher moment of inertia, still can't rev as high or as fast as the shorter stroke. The longer stroke will end up reaching the max piston speed sooner.

It all comes down to how close to the maximum you build the engine. Doesn't matter what power is being made, for any given piston speed, the lower moment of inertia will rev higher and faster. Is the lower moment of inertia due to the stroke? When everything else is at the bleeding edge of what is possible, yes. If you build a light weight, big stroke engine and compared it to a rather heavy short stroke engine, then which ever one actually had the smaller moment of inertia would win.

[blykins]

Thanks Jay, you echoed my thoughts exactly, but with more eloquence....sometimes my brain works but my fingers/mouth don't. 

"It would be correct to say that at a specified horsepower level, an engine with a higher moment of inertia will accelerate more slowly."  That sentence pretty much sums it up. 

[turbohunter]

Not the first time on this forum I had to turn to the ole inter web to look up a definition.

[Nightmist66]

I'm sure rod ratio plays an important role in all of this too.

[Autoholic]

The stroke to bore ratio plays into this as part as part of the corrected piston speed. The longer the stroke, the faster the piston will have to travel and at some point you cannot go any faster due to the speed of combustion is maxed out. The lower your moment of inertia, the quicker the engine will accelerate for any piston speed and this is due force. Think of trying to push a cart and then push a car, at the same speed. You'll be able to reach 5 mph pushing a cart faster than a car. Now imagine having to bring both to a stop, and change directions. Oh and brakes don't exist in this example, for all you clever persons. The shorter the stroke, the higher the engine will be revving for any piston speed and this is due to distance. I should say that when I am talking piston speed, I'm looking at mean piston speed which does not deal with the stroke to bore ratio. The corrected piston speed is used more for determining the longevity of the engine.

Jay, I tried understanding your spread sheet but I can't make heads or tails of it without looking at it personally. There are a bunch of numbers that either should be left alone (like a weight) or have been put into some calculation that cannot be seen. There should also be more inputs. If this was an attempt to see how much torque is needed to rotate and engine at a given RPM, the lower the moment of inertia the less torque is needed with everything else being equal. I'm sure you know personally that this is an over simplified view of the matter though, friction comes into play and that is largely driven by your tolerances. I would recommend that if you want to play with this math in the future, screw the imperial system and just use metric units. So much easier to work with.

[blykins]

It doesn't matter what horsepower or torque is being made

Horsepower does indeed matter and in most scenarios, it matters more than MOI.   I believe you are focused too much on distance/position and not on focused enough on acceleration. 

[Autoholic]

It doesn't matter what horsepower or torque is being made

Horsepower does indeed matter and in most scenarios, it matters more than MOI.   I believe you are focused too much on distance/position and not on focused enough on acceleration.

I am focused primarily on the acceleration. The moment of inertia plays directly into the acceleration. The distance plays into the acceleration, as well. The moment of inertia in statics plays into the force. That force is used to determine the acceleration of the specified mass. The longer the piston has to travel, the higher the piston speed due to that acceleration being constant until it suddenly changes direction. At TDC and BDC, when the piston changes direction it exerts a force, equal to the moment of inertia times the acceleration. It doesn't matter how much power is being made because when you are looking at different strokes and different moments of inertia times the acceleration, you don't know much power (work) is being made (done) and you assume that for the comparison, they make the same amount of power. As such, they cancel each other out. This allows you to focus on the moment of inertia and how the stroke will play into it. The force comes from the fuel exploding and the faster, cleaner it burns the more force it exerts. To figure that out correctly, you need the dynamic compression ratio. But for any specific dynamic compression ratio, a specific amount of force is available upon combustion. That force is broken down as f= moment of inertia * acceleration. The smaller the moment of inertia, the faster the engine accelerates. When you decrease the stroke, the moment of inertia goes down. This results in the acceleration increasing. Due to the distance being shortened, the mean piston speed falls. The increase in the acceleration decreaing the time for the piston to go from top to bottom, increasing the rpm's. Due to the mean piston speed being decreased, the higher the engine can theoretically turn before reaching what is possible.

Having gone through all this, I must now apologize to Jay. His statement about specific power was correct. I had a problem of trying to focus on the power output to dictate what a specific moment of inertia can spin at. If you were to really get into the math, it could be said that the moment of inertia and the dynamic compression ratio is what will determine how much work the engine produces. 

[HolmanMoodyStroppeGang]

Love the data Jay and the engineering conversation, we did a lot of this back when and of course along the way.

Now I am going to refine the question a little for fun.  This is a very broad question.  I am building a full race FE

To me, I also want some bones on the engine, car, clutch, trans, gear,tire, goal and weight, anticipated launch RPM, and if she has a tube chassis, 4 link, and all the combo info. I also wonder, race gas? alky?

Reason why is because I am thinking about ET/cost and hundredths on the time slip too.

I like a heavy Damper on a long stroke engine but at first, wondered the compression, cam, heads, and she has aluminum rods, so....

Clearly I am turning the question on it's head to round out the analysis a little

Is this a 10 second car, goal wise?  950? 900?    850?    And also, how heavy a flywheel do you run, or is it a auto?

If it is a 10 second car, the mass difference will have an effect, on your ET data, but probably very small.  So you might think it all through, chose a quality SFI piece, and maybe say, my next build will be even bigger and faster, and higher revving, so I think I will get something that I can use on future builds too.

No doubt the power level is key, and stroke, as you guys see a lot, a blown car that is full race let's say, tosses the damper, and lets the flange, hub, blowere belt and blower smooth away huge resonant frequencies for that 4,5,6 second blast

Power level is huge, but so is the goal.  The old NASCAR type builds had to live 3,4,5 hours, and our OffRoad FE's had to live, 12,18,24 hours.   

So I would refine the question too, and think horsepower/ET per dollar too

And I want to know, how hard this car likes, or needs, to hit the tire?

Here is an old fact.  Remember Dyno Don's 71 Maverick with a SOHC?  The Pro Stock car that won so much? 

That car liked a low gear, and the tires,chassis, and leave RPM, liked more then more mass.

The 60ft and the ET, picked up, by adding heavier then heavier flywheels, and a bigger dampener

It ran best, because every race car and engine, trans, is, unique to some degree, it worked best with a custom, super duper heavy Flywheel. You guys would laugh if I told you

Reason was, he left sky high, before rev limiters, if he was on a good track, in good air and for the win.  That was a 2 disc car, and the entire combo got tested and tested many ways, so having about twice the weight of a regular flywheel helped him, hit the tire very hard, get the car moving fast, and power shift real high to allow that increased rotating mass to slip the clutch on a gear shift and stay higher in the power band.  Kind of a, try 10 things, and what works works thing

Man, this is such a fun thread by many smart guys.

Race cars deserve race parts, it is nice to just get the best you can budget. ATI and the others will get you to the other end and she sounds fast so NICE WORK man

Loved that chart Jay, thanks to all of you

Just rounding out the issue in case it helps him get that new dampener to the balance shop and spinning

A SOHC can run low 9s with a tricked out stock dampener, not legal, but they got 'pinned'

[Autoholic]

When you want to get into ET's, the power output is not the only concern. Your gearing and the weight of the car matters just as much if not more than the power output of the engine. If you want to run fast ET's, I'd say shoot for the best engine your money can buy and then build the car around that engine's personality. Your preferences will also play a huge part in this. Do you want a high revving engine or do you want it to produce its power down low? Each has their own needs in order to make a reliable engine. I'd say that a torque monster is cheaper to build than a high revving engine. Pick the displacement and go from there. The correct part to do the job can be found using math, however you have to really enjoy it. Once you have the pistons, rings, rods, pins and crank, the correct weight of the flywheel and the damper can be found. At least to get you close enough to pick the part you need from a supplier.

[jayb]

Jay, I'm sorry but I have to disagree with you on this part... "It would be correct to say that at a specified horsepower level, an engine with a higher moment of inertia will accelerate more slowly."

If everything is equal except for the stroke, the longer stroke will accelerate slower than the shorter stroke.

I didn't say anything about stroke in that statement, Joe, I said moment of inertia.  Basically, what this means is that an engine with heavier reciprocating components will accelerate more slowly than an engine with lighter reciprocating components.  Moment of inertia calculations include weight and distance.  Two engines can have the same stroke, but the one with aluminum rods and lightweight pistons and pins will accelerate faster.

On the spreadsheet, here's an example with the crankpin:

crankpin diameter, 2.5", or 0.208 feet
crankpin width, 2.1", or 0.175 feet
crankpin volume then is 0.104' x 0.104' X 3.1416 X 0.175' = .005946 cubic feet
crankpin weight is .005946 X 495.94 (pounds per cubic foot) = 2.949 pounds
crankpin mass in slugs is 2.949 / 32.2 = 0.092

Stroke is 3.78", so radius of the crankpin center of mass is 1.89"
radius in feet is 1.89/12 = 0.1575 feet

Moment of inertia is mass X radius squared, so moment of inertial of each crankpin is 0.1575 * 0.1575 *0.092 = 0.00228 slug-feet.

To calculate torque required to accelerate the crankpin, you need RPM in radians per second.  There are 2pi radians in one revolution, so if you want to calculate the torque required to accelerate at 600 RPM/sec, the math is (600 X 2 X 3.1416) / 60, or 62.8 radians per second squared.  Moment of inertia multiplied by angular acceleration gives you torque, so .00228 X 62.8 is 0.143 lb-ft of torque, to accelerate that crankpin at 600 RPM/sec.

The spreadsheet is an attempt to add up all the reciprocating components of an engine and calculate the power required to accelerate the reciprocating assembly.  Then, the inputs allow you to change something, for example the stroke or the weight of the pistons or rods, and see how much less or more torque is required to accelerate these components.

[Nightmist66]

Here is an old fact.  Remember Dyno Don's 71 Maverick with a SOHC?  The Pro Stock car that won so much? 

That car liked a low gear, and the tires,chassis, and leave RPM, liked more then more mass.

The 60ft and the ET, picked up, by adding heavier then heavier flywheels, and a bigger dampener

It ran best, because every race car and engine, trans, is, unique to some degree, it worked best with a custom, super duper heavy Flywheel. You guys would laugh if I told you

Reason was, he left sky high, before rev limiters, if he was on a good track, in good air and for the win.  That was a 2 disc car, and the entire combo got tested and tested many ways, so having about twice the weight of a regular flywheel helped him, hit the tire very hard, get the car moving fast, and power shift real high to allow that increased rotating mass to slip the clutch on a gear shift and stay higher in the power band.  Kind of a, try 10 things, and what works works thing

I know what you mean. I heard of a guy drag racing a galaxie (can't remember what year), but he used a 90lb flywheel to help launch the car and keep the momentum. He did rev it high on the launch too. It helped to "get all that weight movin".

[ScotiaFE]

Here is an old fact.  Remember Dyno Don's 71 Maverick with a SOHC?  The Pro Stock car that won so much? 

That car liked a low gear, and the tires,chassis, and leave RPM, liked more then more mass.

The 60ft and the ET, picked up, by adding heavier then heavier flywheels, and a bigger dampener

It ran best, because every race car and engine, trans, is, unique to some degree, it worked best with a custom, super duper heavy Flywheel. You guys would laugh if I told you

Reason was, he left sky high, before rev limiters, if he was on a good track, in good air and for the win.  That was a 2 disc car, and the entire combo got tested and tested many ways, so having about twice the weight of a regular flywheel helped him, hit the tire very hard, get the car moving fast, and power shift real high to allow that increased rotating mass to slip the clutch on a gear shift and stay higher in the power band.  Kind of a, try 10 things, and what works works thing

I know what you mean. I heard of a guy drag racing a galaxie (can't remember what year), but he used a 90lb flywheel to help launch the car and keep the momentum. He did rev it high on the launch too. It helped to "get all that weight movin".

This goes against all the thinking today though.
The use of soft loc style clutch's and light aluminum flywheels is the way today.
Less chance of ripping the car apart.
I'll stick with the soft light stuff.

[HolmanMoodyStroppeGang]

Awesome  analysis and I think in this way too.  At FORD we could test everything and it was funny, that sometimes what the analysis suggested, could have this rare anomaly exception, where the car might pick up despite the projections. Same today in some cars, the best DYNO numbers might fall of a smidgen, with a collector that the car like better when the data, from the on car, is factored in. 

I think that how the entire combo ET's as viewed with the on board data, is a factor too. 

What is funny in many fast cars, is when you pull power out of them? Sometimes, they speed up....happens a lot.

So way back then, and often today, a big budget effort, might bring 5 additional parts to the track, to test and mine data from.  You know?

On a dampener, crank life, cam drive life, and valve float issues, bearing life issues, and block life, also factor in a little sometimes.  I like the big dampener idea and the race dampener too, because they are not all tuned internally the same too.

I think his optimum dampener in a clutch car, I presume a 5 speed 2 disc car here, and light, lets guess what the optimum ET dampener might shave or add ET wise too

Not sure we are talking about a few hundredths on lets say a 9 flat car, maybe a negligible and unquantifiable plus or minus too.  I would lean toward the heavier part on the reduce torsional vibration at peak power issue, on the less translation to the cam issue, on the less vibration to the valve train issue, on the crank life issue, on the want to hit the tire hardest, like a car that wants to smack the tires harder then softer, and on the bearing life issue. 

I guess I would conclude like this, in the 60s, a lot of really fast and light AFX style cars, and many blown gassers, injected gassers, and so on, cars with 12.5 to 1 to 13.5 to 1, long cams,fully ported heads, hilborns or enderles, crowers(Stack injectors)just ran a small OD degreed aluminum hub, a gear drive, a glass front clip, straight axle and fuel injection.  These cars did pick up a bit losing a heavy dampener for a real light alloy art with minimal mass.

Now then, light was right on many parts, rods, aluminum valve retainers, aluminum flywheels, aluminum clutch cans and so on.   These were 7 and 8 second cars, but real light.

We did A Gas a lot in the late 60s, early 70s, out here, with the light hubs too, mid 8s, light, clutch flite, clutch C6, clutch turbo era....roller cams, injection, and so on, light valves...trick heads.

Interesting question

Fun to think combos and engineering and I still want to hear about the car/goal/et?chassis and so on. If this is a 12 second car, not even sure how fast we are going, I don't think he will see a difference with a half pound more or less dampener.

This is just me but my concerns on a dampener are more like crank/ bearing life, adding or lessening crank vibration to the cam/pushrods,valves, springs but safety. Not so much ET

Also wonder if he has a billet fully counterweighted crank, not sure

Interesting hypothesis but I wonder.

Fun Thanks

[woodboatwayne]

How would a fluid damper figure into this debate? Built 2 small BBC's before I got the FE bug and used fluid dampers on them and was pleased, but really didn't have a reference point.

[Autoholic]

What is funny in many fast cars, is when you pull power out of them? Sometimes, they speed up....happens a lot.

This is common in all forms of racing. Has to do with better traction, being able to use more of the engine's power without spinning the wheels. It's easy to blow the wheels off of your car in a high horsepower build. While you're spinning, the other guy is winning. This combined with weight, high horsepower engines often weigh more than a little 302. This is what made the 289 Cobra's such a winning combination, the light weight 289 was great for handling and the power was just about right for what you could put to the ground in a Cobra. The 427's weighed more, the FE required a bigger, stronger chassis. The engine also had to be moved more rearwards, this is why they had a reverse Mustang shifter. Sure they look cooler, especially the semi-comp 427's (there are street 427's) but on a track, the 289's were quicker in the corners.

The mention of using a heavy flywheel to help with the launch makes sense. If you want to launch hard, the smoothest transition of power will probably result in the most traction. Makes me think of the rule of 3. I often run into the rule of 3, pick 2. For handling power, it could be something along the lines of power delivery, acceleration / response and reliability / longevity.  If you want smooth power delivery, the rate at which the engine accelerates will probably take a hit as a need to allow smooth transfer of power. If you want it to be quick revving and have a long life, then it probably needs to get the power to the ground quickly (friction is one of the biggest causes of wear). If you want it to engage power smoothly and quickly, the part might not have as long of a life expectancy. Something to think about.

[Nightmist66]

Another three. Fast, good, and cheap. Pick any two.

[jayb]

How would a fluid damper figure into this debate? Built 2 small BBC's before I got the FE bug and used fluid dampers on them and was pleased, but really didn't have a reference point.

I think the theory behind the fluid dampers is that they are self balancing, and are supposed to dynamically help balance the engine.  I try to stay away from them, though.  A long time ago, when I bought my first billet crank from Scat, I asked them about what damper they would recommend.  I was thinking about a fluid damper, but they strongly discouraged that.  They said that they very rarely see a broken crank, but when they do, the snout has been snapped off, and a fluid damper was used on the crank.  Apparently they never had that problem with an ATI damper, which is what they recommended I use.

[HolmanMoodyStroppeGang]

For sure JAY

The were the trick of the week/year there out this way for some years, but then 'issues' surfaced on some builds and ATI and others are top shelf, sure. 

On the flywheel weight, that was a quiet trick for many guys in the late 60's, but what is funny was, well to me,  you had to find a huge thick piece of 4130 or hi carbon steel and made it thick !

No CNC then, tape made pretty automated parts, but in runs because expensive, so the wheel got hand cranked, we did a few, then blanchard ground, press on the starter ring and zero balance it.  Use Mr Gasket High Tensile bolts, long ago.

I'd just add, in early Pro Stock, no rev liters and no leaving on the chip, and you had to really be a good shifter because missing just one shift could kill that pretty race engine.  And no onboard computers, so the seat of the pants feel, got mixed with what the run slip and CREW say out back.  Having sharp guys watching out back can be huge on some fast cars

If this Hot Rodder wants to dial it all in, razor sharp, which is key, he might borrow 3 dampers from friends, find a good track and stable air/temp/DA?Baro and so on, and do a 4 step Great Damper COmparison thing,,,funny and cool !!  But man, you would have to be in a tight tight tight class, against some very very similar cars, to get a meaningful margin of victory out of many cars probably.

I will let some other older FORD guy, from Detroit discuss some of the ways FORD studied this stuff in static pulls for R and D.   We were told and shown, trick test cells that had semi floating mounts and strain gages and pound scales, on fulcrums.   And a few more

The block vibration aspect at the design RPM can be quantified

No kiddlng, I was lucky to meet and learn under some really old guys who did restos on real old V12's for example. In the 60s.  And on some mulit carb V12s, the big deal was a dead smooth idle. So yes, heavy cranks, flywheels, counterweights, rods, front drives,etc. But 3 guys I knew, old pro guys, would do a balance test to know the tune up was perfect once warmed and tuned on the idle screws.  The would set a glass of water and watch the smoothness of the water, then set a penny on it's side on the head.   If the penny could stand, no tip over, on the air cleaner lid, a big lid, or head, and if the fluid was peaceful, they said, perfect

Just a vibration thought on how smooth some reciprocating assemblies, as installed, running, were designed  before WW2..ha ha. Thought is, it could be measured I guess if we just had to know soon, but what ET's the car best always make me happy too. 

Well, ATI won the poll I think.  He sure got a lot of awesome ideads to ponder.  You guys are smart and fast !

[Autoholic]

I never thought about using water as a means to see how smooth an engine idled but that is probably one of the most accurate ways, despite being low tech. Reminds me of something from NASA, not sure if entirely true. NASA wanted something that can write in zero g environment, so they commissioned a company to create the space pen (which is true). Russia had the same need, so they used a pencil. Sometimes the best solutions are low tech, cheap solutions.

[Nightmist66]

Reminds me of something from NASA, not sure if entirely true. NASA wanted something that can write in zero g environment, so they commissioned a company to create the space pen (which is true).

Funny you should mention it, I just happen to have one. Lol. I think you can get them at Staples.

[jayb]

Just for fun I did a few more calculations with my moment of inertia spreadsheet to quantify how much a lighter reciprocating assembly and/or stroke will change horsepower output from the engine.  The spreadsheet includes the weight of the aluminum flywheel I use on the dyno, and also the weight of the clutch plate that bolts to the flywheel, and connects to the input shaft of the dyno.  I started with a harmonic balancer:

Harmonic Balancer Weight                  Torque Required to Accelerate the reciprocating assembly at 1000 RPM/sec
   -  6 pounds (original calculation)               33.876 lb-ft
   -  8 pounds                                            34.153 lb-ft
   -  2 pounds                                            33.323 lb-ft

So, if you reduced the weight of your harmonic balancer by 6 pounds, you would pick up 0.83 lb-ft of torque at the flywheel, when accelerating at 1000 RPM/sec.  (You would pick up more if you were accelerating more quickly, and less if you were accelerating more slowly, but just to limit the variables I've kept to an acceleration rate of 1000 RPM/sec for this analysis).  You'd never see less than one lb-ft of torque on the track of course, so it really doesn't make a lot of sense to go with a lighter harmonic balancer to pick up power.  And if it is true that a heavier harmonic balancer helps with stabilizing vibrations of larger stroke engines, there may be power to be had there, so going with a heavy harmonic balancer is a no brainer.

Next I compared two SOHC engines that I've built over the last few years, 2009's 585" SOHC with the 4.6" stroke and 4.5" bore, and my smaller 511" SOHC with the 4.25" stroke and 4.375" bore.  I have the balance weights for these engines so there is a little less guessing on the component weights used in my spreadsheet.  In 2009 the big engine made 935 HP at 7000 RPM, and when I tested the smaller engine in 2012 it made 840 HP at 7100 RPM.  These engines feature the same basic piston design, the same ring package, and the same connecting rods; the only real difference in these components is the pin, which is a 0.990" pin on the smaller engine and a 0.927" pin on the larger engine.

The numbers come out as follows, for the torque required to accelerate the engine at 1000 RPM/sec:

585" SOHC:  40.081 lb-ft
511" SOHC:  38.813 lb-ft

Not a lot of difference there, and I'm sure the friction from the additional stroke of the 585" engine has a much larger effect than the moment of inertia in this case.  That friction from the rings on the bore, which is a major source of horsepower loss in most engines, would be 8% higher with the larger engine at a given RPM.

However, it is important to note that the moment of inertia losses and the frictional losses are both parasitic losses, and the dyno results for these engines provide horsepower and torque after these losses.  Bottom line:  the 585" engine makes 95 more horsepower than the 511" engine, and it revs faster, with the longer stroke.  I can also vouch for this in the car (my '64 Galaxie).  Net power output is going to trump things like frictional losses and moment of inertia losses in terms of the engine's ability to rev quickly.

Just for grins I did one more, assuming an all out lightened engine, and threw in some really light components like a lightened crank with Honda rod journals, lightweight aluminum rods, a 3.78" stroke crank (stock 427 stroke), etc., but kept the harmonic balancer, flywheel, and clutch plate weights the same.  Torque required to accelerate the engine at 1000 RPM/sec decreased to 25.781 lb-ft, which is a big difference from up around 38-40.  I can see why, in the very competitive arena of class racing or Engine Masters, that getting all the reciprocating weight possible out of the engine will provide an advantage.  But for the expense, the additional 13-15 lb-ft of torque you get from the smaller moment of inertia is a relatively small payback compared to other modifications.  I think improvements in frictional losses, like going with thin, low tension rings, would easily trump the moment of inertia improvements. 

Hope this somewhat esoteric discussion is useful to you guys...

[blykins]

"Net power output is going to trump things like frictional losses and moment of inertia losses in terms of the engine's ability to rev quickly."

Bingo.

Some things go against normal intuition and I think that's why most people picture a big ole heavy rotating assembly and associate it with being a slow-accelerating slug.  However, if they would just wing the throttle on a big inch, high compression, high horsepower engine once, they would see that sometimes normal intuition is wrong. 

Now, as you say Jay, there comes a point where the stroke and piston speed overcome the parts' desires to live happily together....and that point is a limiting factor.  However, making the statement that a long stroke engine can't zip up through the rpms is one of those wives' tales that get passed from site to site.

[turbohunter]

Awesome guys
Thanks

[HolmanMoodyStroppeGang]

Nice engineering JAY, man, thanks for all the numbers crunching, and thumbs up to all.

We all know what Sprint Car engine builders do, and how CUP teams change many perts in a short track versus big track build, I am sure, so the actual observed life and wear of the chosen parts gets learned by using it as designed for 'X" races between freshening.

So there is that line too.  Many Sprint car teams lease the engines, and sign a contract, and leave it alone for 10 -20 races, ship it back, and receive  a fresh mill at the same time.  Several old and good friends out here have a good business doing this for guys all across the USA, and, Australia/New Zealand.   Injected small blocks, all aluminum, Crower or Bryant cranks, Crower or Carillo rods, trick rolled heads, fuel injected, roller cams, best rockers and proprietary cams, pistons,ports, intakes and so on

One line there is obviously, light as possible, to get off the corners sliding, and ahead on a restart, but strong enough to win and live a while. This is a zero failures permissible setting. One engine failure and you are in big trouble reputation wise and, you hurt a mess of expensive stuff.   Like at HolmanMoodyStroppe, with FORD paying the freight, zero engine failures allowed or the shame could kill you business wise.

So this light/lighter/strong/strong enough line is also gained by hundreds and hundreds and hundreds of races, engines,laps, and tear downs.  Build sheets up, tear down sheets down.Data, re testing, heat treating re checks, rockwell it all, all of this stuff,,,,,,zyglo pistons after use, mag everything, wet bath, no dust and an electromagnet, x raying, fastener analysis, it is all applied mechanical engineering and scientific analysis in part, but just patiently learning,,,what works,,,,and what lives   too    and what is fastest

Back when, FORD tested little issues like this more than anybody it seemed, hyper scientifically, but practically too. Well we did.   Go to a race, before the race, and we were lucky, we could get in to test on many tracks due to FORD, and then just run item 1, 2,3 and see how it worked.

FORD was studying so much during the FE days, for example, out here, SHELBY, us, and others, did have trick stuff to use. I did a write up about the sensors and graphs of crank flex testing   The strobing tests done, and so on


For me, on a real fast Drag car, the time slip is the big deal, then what the Crew and Crew chief saw from behind the car, like the tire tracks, tire shake, if it spun the tire, the chassis reaction, then the drivers observations, then the data if it has a racepac, then the regular tuning data, clutch wear, plug condition, leak down, or how the bearings look if you field strip it and all of the rest, lash stability, how the slicks read, you know.  How the data compares to the prior runs, and tune up book based on the past data...

Gosh it is nice to have conversations like FORD guys on a big team simply trying to win and do good work.



k.


All thoughts were very interesting and helped a lot of guys I bet

Still wish we knew more about the car/goal/chassis/past speeds/crew/track/budget/experience and all that

[babybolt]

Actually...

Folks throw around the terminology balancer and damper as if they were the same thing.  Some engines, like Ford's 5.0L need a counterweighted balancer since they are externally balanced.

But for the engines that are being discussed here, harmonic damper would be better terminology since zero balanced is just about mandatory.

The harmonic damper is there for one reason, other than providing a flange for mounting pulleys; to dampen the harmonics of the crankshaft.  The crankshaft vibrates in all sorts of modes, radially, longitudinally like a big banana, etc.  Each firing event in the combustion chambers adds an impulse to the crank.  V12 engines are naturally balanced, followed by straight 6 engines, then 4 cylinders are the worst.  Its all a fairly complicated relation of number of combustion events and at what degree they are feed into the crank per revolution vs the rotating inertia of the crank and the crank stiffness. 

Forged cranks are stiffer than nodular iron cranks and need more damping. 

Automatic transmission converters help dampen the crank vibration.

Some of the harmonics or vibrations are dampened by the oil between the crank and bearings, probably on the order of 25 to 33 %.  This adds heat to the oil.

Probably a small amount is dampened by the windage and oil churning around in a wet sump engine, but not much.

The damper absorbs energy so it can heat up and needs to dispel heat.

The belts, alternator, water pump, etc change the harmonics also.

The OEM's are fairly good at installing a damper that works over most of the engine rpm.   But when you start adding power and switching parts, like stroked crankshafts, you can only guess at which damper weight or types and amount of damping is required.   

[Joe-JDC]

There is one more aspect of this balance that no one is talking about, and that is the rpm that each engine is balanced for, and any overbalance applied.  Until you understand that aspect, then you can neutral balance all the parts to within a cat's whisker, and you will still vibrate until you reach the balance rpm of parts supplied.  No engine is in balance all through the rpm band, only at a specific rpm that must be accounted for by stroke, component weights, rod ratio, camshaft rpm band, cylinder wall preparation, ring tension, oil weight in crank passages, etc., and operating rpm desired.  Sometimes folks get caught up in a specific aspect of horsepower vs torque vs stroke, and make statements that are only valid--sometimes.  Nothing is set in concrete when it comes to the automobile engine's output with today's technology.  Joe-JDC

[jayb]

I think babybolt's comments are spot on, and we should be calling these things dampers, not balancers.  Oh well, old habits die hard 

I know I'm beating this to death, but I really enjoy the topic of parasitics, harmonics, etc.  So I have one more piece of data that some people may find interesting.  Quite a while back, my "dyno mentor" explained to me how you could actually determine an engine's moment of inertia on the dyno.  Any modern dyno allows you vary the acceleration rate of the engine.  For example, my Superflow 901 dyno allows you to accelerate the engine at rates of 50 RPM/sec, 100 RPM/sec, 300 RPM/sec, 600 RPM/sec, 1000 RPM/sec, etc.  You will see different torque and horsepower levels from the engine, depending on this rate, because the faster you have to accelerate the reciprocating assembly, the more torque that will take, and therefore less torque will be available for the dyno to measure.  After talking to him about this (in 2007), I ran home and ran the following test:



The test was done on my 390 stroker dyno mule, the 500 lb-ft and 500 HP engine that I ran many of the tests on in my book.  This is the same engine in back to back tests, done at different acceleration rates.  As you can see there are some variations along the RPM curve, but if you average the torque numbers from 3000 to 6000 RPM for each pull, the difference between the 100 RPM/sec data and the 600 RPM/sec data is about 25 lb-ft. 

So, to calculate moment of inertia for this engine, while it is mounted on the dyno, we need the angular rate of acceleration in radians per second, of 600 RPM/sec and 100 RPM/sec.  So, (600 X 2 X 3.1416)/60 is 62.8 radians/second squared for 600 RPM/sec, and 10.47 radians/second squared for 100 RPM/sec. 

We will call moment of inertia MOM for short.  So, MOM X 10.47 + 25 lb-ft = MOM X 62.8.  Solving for moment of inertia gives 0.477 for this engine.

As a check I plugged my weight estimates for this engine into the spreadsheet, and got a difference of 19 lb-ft between the two acceleration rates, not 25.  However, the spreadsheet does not take into account the part of the dyno that is spinning when the engine is running.  The engine of course has to accelerate the dyno's input shaft and water pump impeller, along with its own internal components.  If I change the value of the clutch plate weight in the spreadsheet from 10 pounds to 40 pounds to try to compensate for this, then the spreadsheet gives the 25 lb-ft difference.  So maybe the dyno's internal parts weigh 30 pounds, or maybe my weight estimates are off somewhere in the spreadsheet.  In any case, its pretty close.

You hear all kinds of things out there about the value of lightweight reciprocating components, but rarely any specifics, so I took this data and made the calculations to try to nail this down within some range (before I spent a bunch of money on titanium connecting rods LOL!).  FYI, I normally run all my dyno pulls at 300 RPM/sec.  Also, given the moment of inertia calculations, it is obvious that in first gear on the racetrack, where the engine is accelerating quickly, you will see a much bigger loss due to inertia than you would in third or fourth gear, where the engine is accelerating more slowly.  If you had the dyno data for the engine at a couple of different acceleration rates, you could take a stab at figuring out how much difference it makes.

OK, I'm done.  Sorry...

[Joe-JDC]

So if you take gear out, it accelerates more slowly, but makes more torque, which accelerates quicker?  Right?  About that lakefront property in Florida?  LOL Joe-JDC

[HolmanMoodyStroppeGang]

Now on step testing, we all probably have Pro Stock friends or similar, and if they use the run data, to program the dyno pulls, that is a fun topic too.   First time I heard a dyno , essentially making a simulated run, was cool, but GO FORD once again, that trick AUTOLITE Dyno we had up on The Hill, did, have a simulation feature, to mimic INDY for OFFY and INDY car engine testing...  Ford can be so serious when it wants to win.  The could spend huge money to help Parnelli, Unser,Gurney and many others, just to get that trophy.  We all saw how hard they tried to simulate a LeMans race in the 60s too. Shifting the trans and all, by servos and tape/computer

Final thought on running no dampner.  Injected A Gasser's / B gassers and similar light, high RPM Drag cars from the 60s, were just fine doing that because an eventual crank break was avoided, because the power and large number of runs, per day, weekend, week, season, often just wore the crank out, 1 grind,2 grind bye, before it broke. 

Remember, some folks would say, well, removing the damper will break the crank, well, eventually maybe. If it is getting run hard enough to need tough triding, or hard chrome, common then, and wears out maybe once a year, who cares if it may break? It doesn't usually was how many guys saw it.  And remember too, by the late 50s, guys were spinning small blocks over 10,000 RPM with a Chet Herbert, roller cam with the rev kit springs over the lifters and some tricks. 

Now here is my old pitch about stock parts are not that bad.....many 10,000 RPM small blocks, based off of a 283 bored and maybe stroked a little, ran,,,true,,,,stock heads, well ported, stock valves, stock keepers, stock stamped rockers, you added trick rocker balls, lol   press in studs with a pin added...LOL   stock main caps, main bolts, head blots, blocks,cranks, rods, rod bolts, oil pumps, pump drives,LOL, no damper...injection or a blower, then an aftermarket cam, magneto,pistons,rings and so on.

Check into the  Velasco Dunn reath Fiat Altered, from 1961-2-3.  That thing was so fast, our old pal Jim Dunn will tell you, or Velasco, "we only flat footed it twice'.  It had too much power on Nitro with only a non stripped 6-71 and a 4 holer( Injector scoop with nozzles).for most tracks. And the engine was 85% stock maybe. 

Just a blown 283, bored tot 301 cubes, in a ultra light glass Fiat.  around 1250 pounds,   Went close to 200 MPH with stock 283 rods,bolts,crank,2 bolt main block and all the above.Stock oil pan...LOL

Point is, you do not need each and every part you see in a JEGS catalog to have a lot of fun, and spend a lot less in come cases .  I bet a modified stock damper would get him close to where he want to go, until he tells us more. ProProducts 427 style, or, get an ATI or similar

The 427 FORD damper did not get a reputation for exploding the inertia ring like the 427 CHEVY damper did, that is for sure.

Cool team meeting

I am sure every poster here could be in the engine rooms of any high budget  top team.

[Autoholic]

Jay, awesome calculations but there is an issue with them on the comparison train of thought. They should increase as rpms increase, for various reasons but one of them is expansion due to heat. As the parts expand, they should increase the friction coefficient a little. What you noted about extreme weight reductions is huge at higher speeds. At higher rpms, the moment of inertia will have much more of an impact on how the engine performs, resulting in higher stresses. That is perhaps the more critical area that moment of inertia becomes important. You don't want to ruin your engine at high rpms because it is simply too heavy. This could be why fluid dampers ended up hurting engines, at higher rpms I could see centripetal force becoming a concern, resulting in an unbalanced harmonic damper. Regular harmonic dampers do not have to worry about this.

[cjshaker]

I've always wondered why nobody ever mentions the truck dampeners. They're big units, similar to the 427 styles. I've used them several times on aggressive street engines and never saw a problem that was related to them.

But that brings up a question, how would a truck dampener be different from the bigger 427 units? Are they made to dampen at a different harmonic level, and if so, how are they tuned for it? Is it the size of the inner hub vs. the outer ring? Just the thickness of the outer ring? I've honestly never looked at them close enough to see if/where there were differences.

For a fast reving drag only engine, I also wonder how essential it is to choose the "right one". The engines move through the harmonic phases so fast that it almost seems pointless. But I can see the benefits if it is "tuned" for the highest frequency, since that is likely where the majority of its time is spent. I believe there was a discussion some time ago about the order of harmonic frequencies and at what RPMs they occur in a 90* V8 engine.

[ScotiaFE]

Beating that horse some more. 

SFI SPECIFICATION 18.1
5.1.3 PROCEDURE
A.  Mount the damper to the spindle and attach the tachometer.
B.  The damper shall be driven to a rotational speed between
12,500 and 13,500 rpm and maintained at that level for one
hour.

It would be hard to say that any damper tested to this level is not up to the task on
most FE's. jmo

[jayb]

Jay, awesome calculations but there is an issue with them on the comparison train of thought. They should increase as rpms increase, for various reasons but one of them is expansion due to heat. As the parts expand, they should increase the friction coefficient a little. What you noted about extreme weight reductions is huge at higher speeds. At higher rpms, the moment of inertia will have much more of an impact on how the engine performs, resulting in higher stresses. That is perhaps the more critical area that moment of inertia becomes important. You don't want to ruin your engine at high rpms because it is simply too heavy. This could be why fluid dampers ended up hurting engines, at higher rpms I could see centripetal force becoming a concern, resulting in an unbalanced harmonic damper. Regular harmonic dampers do not have to worry about this.

Yes, frictional losses and heat are not included in the calculations; there isn't really a good way to estimate that, as far as I know.  But I don't think the expansion of the engine due to heat will have a significant impact on moment of inertia; certainly less than 1-2%.  After all, the reciprocating assembly can't expand too much, or you'd get piston to valve clearance issues and probably other clearance issues also.  Of course you are correct about frictional losses increasing dramatically with engine speed, but frictional losses are not part of the moment of inertia calculation.  And I don't agree that at higher engine speeds moment of inertial will have a larger effect.  Look at the dyno data; if you average it out it is about the same from 3000 to 6000 RPM.  Where moment of inertia grows in importance is with the acceleration rate.  And that's all part of the formula for calculating torque required to accelerate the engine.

[jayb]

So if you take gear out, it accelerates more slowly, but makes more torque, which accelerates quicker?  Right?  About that lakefront property in Florida?  LOL Joe-JDC

Actually that's right Joe, but the small amount of additional torque you get from accelerating the engine more slowly is far outweighed by the massive amount of torque you lose to the wheels by gearing down.  If there's one thing that the moment of inertial calculations point to, its that it is not that large of an effect.

Send me that real estate brochure, will you?   

[jayb]

For a fast reving drag only engine, I also wonder how essential it is to choose the "right one". The engines move through the harmonic phases so fast that it almost seems pointless. But I can see the benefits if it is "tuned" for the highest frequency, since that is likely where the majority of its time is spent. I believe there was a discussion some time ago about the order of harmonic frequencies and at what RPMs they occur in a 90* V8 engine.

I'd have no idea how to choose the right balancer; the rule of thumb that I use is a bigger stroke needs a heavier harmonic balancer (oops, damper!).  I'm sure there's more to it than that, but I'm not aware of the details.

[plovett]

Inertia is a straight-line measurement... think of when you're driving in your car and you tap your brakes....your body wants to continue in the same direction it was headed. 

The moment of inertia is not really a time based unit, but it's a measurement of an objects resistance to changing rotational motion.  In physics/engineering, a moment is a tangential force which makes a torque. 

So in a rotating assembly, the crankshaft would have a moment of inertia, which would affect its ability to accelerate or decelerate quickly. 

I'm not sure what you're getting at here.  Moment of intertia, or rotational inertia, is not a time based unit.  Linear inertia is not time based either.  They're both inertia, whether linear or rotational. 

Anyway, I've been trying to squash that old saying, "a short stroke engine revs faster" for ages.  I'd be talking to somebody and they're comparing say, a 440 Chrysler to a 340 Chrysler.   They say something like, "Well the 440 makes 100 more horsepower, but the 340 will rev quicker".    It might with no load on it.  But when the weight and inertia of the car and all it's rotating components are added in, the weight and inertia of the rotating assembly becomes a much smaller percentage, and much less important (for acceleration anyway). 

Now if the 340 made the same hp as the 440, presumably at  much higher rpm, and could use a lower gear ratio, then that's another story.

A lot of the time, in my opinion, rpm limits have more to do with valve train stability than with piston speed or bottom end strength .  So you could just keep spinning the big long stroke engine faster, but only up to a point.

I hope I'm not getting off topic.  Interesting discussion in any case.

JMO,

paulie

[blykins]

I was replying to the guy with the post in front of mine.....he was asking about the moment of inertia and was thinking it was something related to time.  I replied and said it was not a time based unit. 

[plovett]

Inertia can be linear or rotational, and neither is time based.  I guess the way you worded it made it sound like (to me) you were trying to say something different.  Just making sure I'm on the same page.  It appears so, Kimosabe. 

Thanks,

paulie

[Drew Pojedinec]

As a qualified Engineer, I feel I need to weight in on all of this.














"I like a black balancer with white letters.... the shiney ones are annoying and hard to read when you hit them with a timing light."

[mike7570]

The way I picked one when I  built my first super-street car in 1983. 
Who makes an SFI damper for the Ford FE.........anyone?
I had 1 maybe 2 choices, I used the shiny black one also.

[whitea62.7t]

The Brain POWER on forum is Astounding
Thank You Guys

[Autoholic]

To truly squash the shorter stroke will rev faster, you need to look at very different strokes. Changes of say half an inch in stroke won't make a drastically different engine. Compare a 2.2" stroke to a 4.2" stroke though and you will see a very different attitude for each engine. Also, to really get into the rev abilities of the rotating masses, you will most likely need overhead cams. I think the pushrod engine largely limits what an engine can do and your ability to see the limits of the crank, rods and pistons. Think Formula 1.

[plovett]

To truly squash the shorter stroke will rev faster, you need to look at very different strokes. Changes of say half an inch in stroke won't make a drastically different engine. Compare a 2.2" stroke to a 4.2" stroke though and you will see a very different attitude for each engine. Also, to really get into the rev abilities of the rotating masses, you will most likely need overhead cams. I think the pushrod engine largely limits what an engine can do and your ability to see the limits of the crank, rods and pistons. Think Formula 1.

I think it's true that most hobby engine guys, mechanics and machinists, even accomplished pro engine builders, tend to operate with variables of limited range, dictated by the type of engines they build.  That could make it harder to see subtle trends within the "noise" of all the other variables.  I could be wrong.  I'm only a hobby engine guy. Maybe the pro guys can say definitively what a 1/2" stroke difference will make with "all else equal" and "with all else not equal".  I say that because it's not often that you change one variable without changing several others at the same time.   I'm only speaking in vague generalities and I'm now going to bow out to those with actual experience in these matters.   

paulie

[Drew Pojedinec]

Lotta folks like to take a little bit of info and take it out of context as well.

Not trying to single you out Joe/autoholic, but comparing the stroke of a 390 vs 445 for instance, doesn't require a F1 race engine reference.  Not that you aren't correct, but the application makes it irrelevant.  I'm pretty certain I'd prefer a 500hp 445 in my Galaxie over a 500hp F1 engine  
Just like the recent debate (which was awesome and informative much like this thread) about Iron VS Aluminum blocks.
I can totally see where the aluminum block doesn't make as much power.... makes total sense.  The references to top tier race engines tho do not hold much for those of us looking at a 550-600hp 482 engine.  In their scenario there may be a 30-40hp difference, but for a 550hp 482 that I'd toss together there might only be a 5hp difference, or none at all.

[jayb]

"I like a black balancer with white letters.... the shiney ones are annoying and hard to read when you hit them with a timing light."

Now that is a savvy engineering comment!

[Autoholic]

Lotta folks like to take a little bit of info and take it out of context as well.

Not trying to single you out Joe/autoholic, but comparing the stroke of a 390 vs 445 for instance, doesn't require a F1 race engine reference.  Not that you aren't correct, but the application makes it irrelevant.  I'm pretty certain I'd prefer a 500hp 445 in my Galaxie over a 500hp F1 engine  
Just like the recent debate (which was awesome and informative much like this thread) about Iron VS Aluminum blocks.
I can totally see where the aluminum block doesn't make as much power.... makes total sense.  The references to top tier race engines tho do not hold much for those of us looking at a 550-600hp 482 engine.  In their scenario there may be a 30-40hp difference, but for a 550hp 482 that I'd toss together there might only be a 5hp difference, or none at all.

It wasn't about the application. The whole point was the vast difference between 6000 rpm 16000 rpm and the stroke is roughly different by an inch to two inches. So there is something to be said about short stroke engines revving higher and faster. In the same post though, I pointed out that a half inch difference in stroke might not make too big of an impact on how fast or how high and engine can rev. It will certainly make a decent difference in power output but the way the engine responds might not be as predictable as my other example. So I'm bringing up the point that the saying shorter strokes will rev faster and higher might be dependent upon how big of a difference are we talking? Jay has already shared info that his bigger stroke SOHC responds faster.

If we really want to get into the math behind what is possible with any stroke, we can look at the equation for mean piston speed. MPS = 2*stroke*RPM. Racing engines and high performance engines will range from 20 m/s to 30 m/s. You can find the MPS of some high performance engines to give you an idea. For an engine you want to put in a street car, I wouldn't push it much past 25 m/s. So if we use 25 m/s as our limit, the equation will look like this, with an example. This will tell you roughly how high you can run any stroke, it won't tell you about the stresses involved and how quick it will rev.

25.6 m/s =  2 * (96 mm / 1000) * (8000 rpm / 60)

The 1000 is a conversion from mm to m and the 60 is to convert rpm to rps. 96 mm is roughly the stroke for the 427 FE. The SOHC I believe can run this high without much of an issue and I've seen the valvetrain testing that says you can go higher if you use the right parts. At 9000 rpm, the 3.78" stroke has a mps of 28.8 m/s, which is probably only possible on racing gas. The coyote though for example runs something like 25.5 m/s at 7000 rpm.

I was doing some calculations on MPS and I remembered something from a Formula 1 documentary, I believe it was Cosworth behind it. They were struggling with reaching the RPM level they wanted (20,000 RPMs!!!). As they would get close to it, the engine would hit a wall. They were struggling with getting all of the fuel to burn. Their solution was to increase the fuel pressure. This increased the dynamic compression ratio and resulted in a better burn. Now the issue with increasing fuel pressure is that you most likely will increase the temperature of the combustion, so you have to watch out for this. It is something to think about for you guys though, increasing the fuel pressure could result in some rather nice gains. I'm not sure if I know of any practical ways to check combustion temps and pressures though...