A six cylinder inline engine, or pretty much any engine using a crankshaft needs a harmonic balancer to absorb harmonics that get induced in the shaft at various orders. Without a damper, the crankshaft will quickly fail.

Many drag racers that run belt driven superchargers do not use harmonic balancers, citing the blower drive belt as serving that purpose with few ill effects. Most of those racers take engine's apart between events, or even between runs, so some of the effects may be long term, and indistinguishable from normal wear.

I find that most of those that don't run them are not engineers, but tend to be builders and machinists. They also tend to have odd issues with bolts coming loose in various locations. For instance, the timing cover bolts backing out on BB drag or Monster Truck engines.

As I look through the harmonic issues of the inline six engine, I see severe harmonic orders that could result in catastrophic shaft failure. Do we have any engineers on board here that can work up the pros, cons and any contribution of a blower drive belt used in lieu of a harmonic balancer for a supercharged drag race engine? While the engine won't spend any periods under load at a constant engine speed, it concerns me that the crank shaft can still operate at those harmonic speeds long enough to be subjected to fatigue, and ultimately, failure.

CJ

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Part of Tyrde-Browne Racing

What are you running on the back end of the motor?(Torque converter....clutch and coupler?)

Can you run a damper on the front end?

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I have an ATI superdamper that has provisions for a blower drive, however, with a crank hub, the drive can be positioned further back on the crank snout. This reduces the load on the snout. The ATI is also a tank. It weighs as much as a medium sized poodle.

While the engine uses a torque converter, it doesn't effectively absorb harmonics like a damper does. First, it is not directly mounted to the crankshaft, and would not respond to harmonics in a way to deaden the twisting forces at the orders where the engine would be operating based on it's dimensions.
The ATI is SFI approved, though I need to send it in to be re-certified. I have a sticker for it. Someplace.

The question would be, does the drive belt actually absorb harmonics? Based on my understanding of the problem, I don't see how it could be effective doing so. While low order harmonics may be dampened by the drive belt, higher order harmonics would look at the belt as an external accessory, should they be transmitted effectively to it at all.
My math isn't fresh enough to work this. Maybe I need to go back to the books for a while.

CJ

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Part of Tyrde-Browne Racing

I run a TCI Rattler....definatly takes out harmonics. I dont know about a blower.....you run them on street blown cars though.

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Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

One thing that makes harmonics come into play is the bending of the crank. A crank bends more due to certain things, like RPM, load, and power increase. One advantage you will have over others is that you have a billet crank, where others more than likely will only have the stock forged or cast crank. This being an advantage to you because the billet crank is going to be more resistant to the bending stresses imposed on it and won't show harmonic problems at the same RPM, load or power outputs as stock cranks will. The belt will also dampen them to some degree as well. So you may not be as bad off as you think you will be. Aluminum rods dampen harmonics in inlines very well, while steel and titanium do not.

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There's no such thing as too much cam....only not enough engine!

Good to know!

Still beating myself up second guessing stuff. If it was a street engine I wouldn't be asking, the balancer would be mounted.

I'll go with the Hub on this engine.

Thanks!

CJ

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Part of Tyrde-Browne Racing

I cant see the belt absorbing a large percentage of the harmonics. It might absorb some....but is it in the range you need?

If bending the crank adds more harmonics then damper plus belt drive seems to be counterproductive.

You need a damper mounted on the rear of the crank ....that mounts the flexplate and TC......or drive the blower off the rear of the crank.....

How many HP to drive the blower?

If I knew the math....I would calculate it incorrectly.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I would run the damper to keep the crank harmonics out of the valve train. David Vizard makes more power with a heavy damper on a Chevy than with a light damper and he credits valve train stability. With the size of the crank snout and the main bearings I am not concerned about the extra length.

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Joshua

Good input. Well, now I need to call ATI.

Thanks for all the input. Time to get some parts on the way.

CJ

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Part of Tyrde-Browne Racing

Damper or no damper you are still going to shake bolts loose. Red Loctite will be your friend, but you will still have a weekly ritual of checking for loose and missing bolts.

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Official Cookie and Mater Tormentor.

Not to mention the loose nut behind the wheel

Richard

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Part of Tyrde-Browne Racing

And that nut will likely do more damage than any of the other loose fasteners!

CJ

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Part of Tyrde-Browne Racing

My car loosens bolts every event.....So I am sure you are in for it too!

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Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

No doubt! Your car loosens bolts on my car when your staging!

I need to pull the Hooptie out of the back yard and give it the spring check out. Haven't touched it since the hard freeze. The anti-freeze went to slushy in the radiator. I let it thaw on it's own. It hasn't been that cold on the valley floor since '72. The arthritis in my hands still hasn't recovered.

CJ

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Part of Tyrde-Browne Racing

I don't think I've ever heard of a racer getting his nuts loose on another racer's ride in the staging lane...that explains the pretzeled pushrods on Andrews ride and the odd colored paint transfer on the Hooptie...

I think I'll go back to just wrenching on street cars after that...at least they only complain about upgrading to an oversized tailpipe, and bigger intake...