Destroying the dogma: lightweight crankpulleys

[Trab]

Im sure that even more people have blown up there engines due to not having oil... But that doesnt really prove anything...

[Atrosity]

This is the reasons why I won't change out my crank pulley. I won't even change out my driveshaft just because it is pointless.

[Ninja Performance]

I've got nearly 50k miles on my engine using lightweight flywheels and crank pulleys... no problems. I had an Unorthodox on there for 40k of it, but I got tired of my headlights flickering when at idle sometimes, so I put a 3SX stock sized one on about 10k ago. I've had a UR flywheel for that same time period also.

Honestly, I still can't believe people argue about this, it comes down to personal preference. I prefer having a lighter rotating assembly, and sticking with a td04 based turbo, running a max of 18-19 psi. Far more people have blown up their engines due to overboost conditions than have ever screwed up an engine due to ditching the harmonic balancer.

Sounds like your setup is "low power", which I don' t have a problem with using a non OEM pulley. Once you are over 500-600AWHP, I would highly recommend it.

-Chris

[UTRacerX9]

The power of the car has little to do with it. I've been running 13T's for years, and they put out decent power, I've got a 19T sitting in a box waiting to be installed because I wanted to do a 13/19T combo. My goal has always been 11.7 or thereabouts, so no need to go with a td05 setup.

My car still spins to a 7k redline, and if harmonic balancing is what we are debating here, it makes little difference how much peak power an engine can put out, what matters is whether the engine is balanced or not. For 50k miles, I for one have had no problems, and I don't baby my car when I drive it. I suspect most people who have had an engine failure and blamed it on a crank pulley would have lost their engine with the stock pulley too, for whatever reason.

[i3igpete]

The power of the car has little to do with it.

My car still spins to a 7k redline, and if harmonic balancing is what we are debating here, it makes little difference how much peak power an engine can put out, what matters is whether the engine is balanced or not.

no, power has EVERYTHING to do with it. harmonic balance is twist of the crankshaft. twist is torque - power depends on torque and RPM. if you'd read what i wrote before, typical vibration torque (TWIST) can be 4 or more times the brake torque. 500 ft lbs going out the clutch = 2000+ ft lbs of torque at the journal.

balance is centrifugal force. centrifugal force depends on counter weight.

they are two completely different things.

saying "my car is fine" is one thing. but please don't mix up concepts - it's very misleading to owners that don't know any better. centrifugal force and torque are two very clear, very different things.

[bluemax_1]

What I personally wonder about is how much difference it would have made to the high HP cars running undamped pulleys, as to when they begin developing cracks in the journals. I recall reading about those cars a few years back when there were a lot more people saying, "undamped pulleys are fine" before a few of us began bringing up the difference between balanced and damped.

Heck, IIRC, more than a couple of owners didn't even realize their journals were cracked till they did a preventive teardown and magnafluxed the crank. Of course, I think there was at least one that found out when they broke the crank.


Max

[J. Fast]

no, power has EVERYTHING to do with it. harmonic balance is twist of the crankshaft. twist is torque - power depends on torque and RPM. if you'd read what i wrote before, typical vibration torque (TWIST) can be 4 or more times the brake torque. 500 ft lbs going out the clutch = 2000+ ft lbs of torque at the journal.

To an extent, but not entirely. As the article summarized... it has very little to do with power, but the design and relationship between the pistons, rods, crank, and material coefficients. If you change the mass or frictional coefficients of any these items in an engine you will change the natural frequency of an engine. It would be an absolute miracle to see a 6g72 engine with Pauter rods, Wiseco pistons, and and custom fit bi-metal or tri-metal bearings, produce the same natural frequency on the same crank, it's just not going to happen. The crank is still going to twist and you will experience torsional vibration but the natural frequncy must and will change.

If you modify your engine from stock, an oem dampener serves no purpose, the natural frequency of your engine will be different then stock so what purpose does a stock dampener even serve? Since the stock balancer is designed with a specific vibration frequency in mind, with a modifeid engine you are just as well off without one. (until fluidampr makes us one )
From the lips of Jack Kane (RET) Race Engine Technology, SAE, AAMI Design Development Engineering:

" One aftermarket device, the Fluidampr™, is an example of a damper. It dissipates energy by transforming it into heat by shearing action in a high viscosity fluid. Some race car people seem to like it, but it is banned from the top levels of NASCAR racing, because with extended use at high levels of energy dissipation, the polymers in the shearing fluid become rearranged and the fluid then settles off-center when the engine is stopped. Next time it is run, the nose of the crank is horribly out of balance, and there's a short run from there to cranksaft failure.

...modifications to an original engine design which affect crankshaft stiffness and / or system MMOI (stroke, counterweights, bobweight {therefore counterweight} mass, clutch and flywheel MMOI, etc) will change the system resonant frequency. In order to determine the correct solution for a particular engine combination, the engine designer must a) do the measurements to determine the critical frequencies in your application and (b) and design or obtain an absorber tuned for the correct order or frequency, as fits with the application.

For any application which operates at high power and a relatively constant speed for long periods (unlike a race engine which typically cycles up and down quite rapidly and only has to live a few hours), it is critical that the major orders of crankshaft torsional vibration be attenuated.

Whatever device is used to absorb crankshaft internal torsional vibrations, it has an effect (usually small) on the excitation produced at the loaded end of the crankshaft around resonance. That device, together with the Mass Moment of Inertia of the devices attached to the output flange of the crankshaft, will affect not only the value of the crankshaft resonant frequency, but also will influence the longitudinal location of the torsional node on the crankshaft.

The fact that a crankshaft is running through a wider RPM band and doing so rather quickly suggests that the crankshaft doesn't spend much time at any critical frequency. The bigger issue with crankshaft torsionals in a high performance engine is the level of excitation into the valvetrain, which detracts from the accuracy of valve motion.

Jeremy

[MaxClass]

So you are saying that once you go forged pistons [mine are Wiseco’s] and other mod’s you have actually changed the frequency of the whole system? That makes sense to me.

Then if the stock pulley is designed for the stock frequency system and you change it then you have a whole new ballgame. I had the machine shop balance the works with aluminum pulley and flywheel I plan to run so it should be better than using the WAG approach. If not I would appreciate any additional input on this subject from anyone knowledgable on this stuff.

It’s not a matter of life or death, it’s more important than that.

It also sounds, if I’m getting any of this, like how strong the frequencies are are also dependent upon the amount of power directed into the system at any one time. Seems like cruising along at 2500 rpm’s pulling vacuum should not induce a lot of frequency problems until you get on it, then the twisting really begins as the rpm’s go up and additional frequencies are encountered.

I find this a fascinating discussion. Something like what you would find on 3STech.

Is this compatible with "String Theory"? Michio Kaku didn't mention this in any of his books.

[pos-vr4]

Think about your common "power pulleys." They may add some power by slowing down all of your accessories, but they will hurt your engine life and your power at some RPM ranges. Power Pulleys are not the right way to make power. In the long run power pulleys will yield failures in your engine and components on your car. That stands true for Imports and American cars. Read more about the Dangers of Power Pulleys on ATI's web site, www.atiracing.com.



I found this expert out of an ATI article from last year

IMO neither an OE pulley or a power pulley is BEST for a big power 3s application, but a New OE pulley would be the prefered way to go with what we have to work with.

[J. Fast]

So you are saying that once you go forged pistons [mine are Wiseco’s] and other mod’s you have actually changed the frequency of the whole system? That makes sense to me.

Then if the stock pulley is designed for the stock frequency system and you change it then you have a whole new ballgame. I had the machine shop balance the works with aluminum pulley and flywheel I plan to run so it should be better than using the WAG approach. If not I would appreciate any additional input on this subject from anyone knowledgable on this stuff.

It’s not a matter of life or death, it’s more important than that.

It also sounds, if I’m getting any of this, like how strong the frequencies are are also dependent upon the amount of power directed into the system at any one time. Seems like cruising along at 2500 rpm’s pulling vacuum should not induce a lot of frequency problems until you get on it, then the twisting really begins as the rpm’s go up and additional frequencies are encountered.

I find this a fascinating discussion. Something like what you would find on 3STech.

Is this compatible with "String Theory"? Michio Kaku didn't mention this in any of his books.

I think the most important thing to remember is every engine is different. As soon as you change the weight or composition of one component tied to the crank, the natural frequency will change aswell as the 3rd order or 4th order frequency being discussed. Therefore a dampener will only work if designed for each unique engine. Just don't go driving around at a constant 5000 rpm's for a 1/2 hour. Run through the gears.

Jeremy