harmonic balancers

[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