harmonic balancers

[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