What's better A timing chain setup or a gear drive setup

[hoffman900]

Some Honda stuff:

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Another thing Billy has mentioned is how Sprint Cars couldn’t get away with the lobes they use if it weren’t for the camshaft drive pumps acting as dampers.

[Jeff Lee]

The question cannot be correctly answered without understanding the effectiveness of the damper and is the engine operated in a range where a critcal crankshaft exciting order lines up with a crank torsional vibration mode. You will have rpm points where the excitation and modes do line up, the question is where, how bad, and are you running the engine there. Then the next question is does the crank damper control it and keep the torsional vibration amplitude peak to peak under control.

If the answer is the crank is subject to significant torsional vibration a gear drive will be worse. In F1 they invented torsional dampers in the gear drive to fix that and not transfer it to the cam, probably there is one in that mess of gears in the picture above. IF you have a crank torsional signature you should probably run a belt.

It is a system so there is no one size fits answer. The OEM's have the engineering for this, the aftermarket usually does not.

For what it’s worth, I have an ATI Dampner and I sent it to them for a rebuild. They changed the durometer of the o-rings for the RPM I operate at. Launch 6800-7200 RPM, shift at 8,000 RPM, lights at 8,000+

[Ken_Parkman]

ATI has a lot of experience, but unfortunately there are a lot of factors and unfortunately they would not have as much AMC experience. I know at least a few years ago they had the equipment and did torsional vibration amplitude measurements which is a lot better than most aftermarket dampers who do not even know what a damper does. Problem is we do not have crank frequency modes. I was going to try to get a crank into the vibrations lab at work years ago but that never happened. Even then it would be different if the crank stiffness (bearing size or offset grind) or weights (flywheel/clutch) changed. For excitation I think the 1 1/2 and 4th orders would be the critical ones at high rpm with a stock AMC firing order. But not much good without some real vibration lab data. Also not sure what a firing order change would do to this.

This stuff is so complicated your head will explode. I did discuss with a world level rotordynamics expert and my brains started to melt and run out my ears. He dug out the Den Hartog text and I read that for a while. Back to brains melting and running out your ears. You learn tremendous respect for the power of vibration to bust stuff.

One thing to look at is the condition of the timing chain. If the chain is being beat up there is more likely to be a poorly controlled mode there. Most people try to fix the symptom which is the chain, and not the problem which is the damper.

[hoffman900]

ATI has a lot of experience, but unfortunately there are a lot of factors and unfortunately they would not have as much AMC experience. I know at least a few years ago they had the equipment and did torsional vibration amplitude measurements which is a lot better than most aftermarket dampers who do not even know what a damper does. Problem is we do not have crank frequency modes. I was going to try to get a crank into the vibrations lab at work years ago but that never happened. Even then it would be different if the crank stiffness (bearing size or offset grind) or weights (flywheel/clutch) changed. For excitation I think the 1 1/2 and 4th orders would be the critical ones at high rpm with a stock AMC firing order. But not much good without some real vibration lab data. Also not sure what a firing order change would do to this.

This stuff is so complicated your head will explode. I did discuss with a world level rotordynamics expert and my brains started to melt and run out my ears. He dug out the Den Hartog text and I read that for a while. Back to brains melting and running out your ears. You learn tremendous respect for the power of vibration to bust stuff.

One thing to look at is the condition of the timing chain. If the chain is being beat up there is more likely to be a poorly controlled mode there. Most people try to fix the symptom which is the chain, and not the problem which is the damper.

I know ATI has the equipment but the decade plus old number I read somewhere was at least $5k to start, but don’t quote me on that.

BHJ has a great white paper on this, but as you point out, it’s all their best guess short of measuring it.

A friend is an engineer working on helicopters and deals with this. He is 10x smarter than me and he tells me his coworkers make him feel dumb.

[GARY C]

Then I was reading a thread here on ST about crankshaft dampening and gear drives were put down because it was said, they cause to much detrimental cam harmonics????

Blame HP Books, S.A Design etc that everybody grew up on.

Some of the best historical engines had gear drives.

No idea what this is but it has lots of gears.

But over time they all changed to belts or chains, maybe because gears were not as good as they thought?

[GARY C]

Then I was reading a thread here on ST about crankshaft dampening and gear drives were put down because it was said, they cause to much detrimental cam harmonics????

Blame HP Books, S.A Design etc that everybody grew up on.

Some of the best historical engines had gear drives.

No idea what this is but it has lots of gears.

Every F1 and Indy Car engine in the last 45+ years has had a gear drive.

Cosworth figured this out 60 years ago and there are modern takes on it plus quill drives. Honda has a few papers on reducing angular velocity variations in their F1 engines from 20 years ago.

Cosworth style damper, quill drive that grabs the cam along its length, weighed cam gears, locking the cams at the rear, dampers on the read of the camshaft, etc.

Billy Godbold has shared data on the measured flucuations on a Pro Stock engine.

So?
900+ HP 10,000 RPM pushrod Cup engines all had Belts, Is it possible that it's application specific and just because Honda and F1 doesn't have a "White Paper" on it doesn't prove it wrong?

[hoffman900]

Blame HP Books, S.A Design etc that everybody grew up on.

Some of the best historical engines had gear drives.

No idea what this is but it has lots of gears.

Every F1 and Indy Car engine in the last 45+ years has had a gear drive.

Cosworth figured this out 60 years ago and there are modern takes on it plus quill drives. Honda has a few papers on reducing angular velocity variations in their F1 engines from 20 years ago.

Cosworth style damper, quill drive that grabs the cam along its length, weighed cam gears, locking the cams at the rear, dampers on the read of the camshaft, etc.

Billy Godbold has shared data on the measured flucuations on a Pro Stock engine.

So?
900+ HP 10,000 RPM pushrod Cup engines all had Belts, Is it possible that it's application specific and just because Honda and F1 doesn't have a "White Paper" on it doesn't prove it wrong?

A gear drive to do it right would have to require re-engineering the entire front end of those blocks, which would mean new blocks, which good luck letting NASCAR allow.

[ClassAct]

I run a belt on my current setup, going back to a gear drive. There is a lot of bs out there about them. First off, Pete Jackson or similarity gear drives are junk...pure junk.....secondly, the whole "gear drives transmit damaging harmonics to the valve train" is a bunch of bs as well. I've had the opportunity to talk to the engineers at Milodon and recently RCD about this....MYTH! Fixed idler, full cover style gear drives don't transmit anything more to a cam than a chain or belt.....if they were such an issue, the high end exotic cars wouldn't run gear trains.

I’m going to test it and post my results just because. I won’t have a belt drive unless someone wants to donate one for a SBM, but I’ll do a Milodon fixed idler against a chain.

You
Did that test ever happen? See my recent post on ST regarding HP loss on Gear Drive. Thanks.

Not yet. I was hoping to do it this weekend but the guy isn’t wanting to do that test right now. So I’ll do it on my own stuff in a couple of months.

[Alaskaracer]

I'll stick with gear drives and either a fluidampr or a pendulum damper like tci used to make.....

ATI can suck it on their dampers......

[Alaskaracer]

But over time they all changed to belts or chains, maybe because gears were not as good as they thought?

It's called marketing......and everybody has bought into it......

[Tom68]

But over time they all changed to belts or chains, maybe because gears were not as good as they thought?

Well they didn't all change, but for passenger cars it's the quietest cheapest thing that'll do the job that gets picked.

[hoffman900]

But over time they all changed to belts or chains, maybe because gears were not as good as they thought?

Well they didn't all change, but for passenger cars it's the quietest cheapest thing that'll do the job that gets picked.

Anything gears requires setting backlash, etc.

Throw a belt or a chain on and let the tensioner take care of it. Easy, fast, and in OEM’s cases, cheap (which equals profit).

[Alaskaracer]

Many OE that have used belts are now going back to chains....wonder why that is......
Diesels and very high end exotics use gears......you'll never see a belt on one either....or an elastomer damper for that matter, they use fluid dampers....


I'm gonna get flamed for this but belts and elastomer dampers are way overrated and over sold. Fluidampr is actively working with NASCAR as we speak to replace the elastomer dampers that they currently run. There is also an old rumor that fluidamprs were breaking crankshafts and that's why you don't see them....all BS....never happened....

[bob460]

Steve Morris use's gear drive's on his SMX 4500+hp monsters!

[Warp Speed]

Many OE that have used belts are now going back to chains....wonder why that is......
Diesels and very high end exotics use gears......you'll never see a belt on one either....or an elastomer damper for that matter, they use fluid dampers....


I'm gonna get flamed for this but belts and elastomer dampers are way overrated and over sold. Fluidampr is actively working with NASCAR as we speak to replace the elastomer dampers that they currently run. There is also an old rumor that fluidamprs were breaking crankshafts and that's why you don't see them....all BS....never happened....

Ya, Fluidampr is trying to replace the ATI elastomer, but continue to fail miserably! Lol
I've tested more of that shit than I care to think about.
Your making strong statements as if thwy are gospel, have you done any actual testing on the two subjects?
Not "flaming", serious question.