[Steve C.]

Of interest and related....

The new Feb issue of Popular Hot Rodding has a 15 page tech article written by David Vizard titled "The Spin Zone". Eight ways to get big rear-wheel power increases without having your engine make one hp more.
The big emphisis of the article discusses the subject of "flywheel moments of inertia" and the low/high moment moment of inertia flywheel controversy (or do I use a heavy flywheel or light flywheel, which is better?).
Other subjects are tackled... driveshaft, axles, wheels, etc ... and the other "flywheel" which is the crankshaft tortional vibration damper, or crank damper for short.
No matter what rules seem to apply to a given situation, there always seems to be an exception. The moment of inertia of an object up at the front end of the engine is just such an exception. Its the crank damper. Back in the '80's, even top drag racers were substituting heavy crank dampers for lightweight aluminum "hubs" in the belief they would go faster. The reality is these hubs, although having a vastly lower moment of inertia, actually cut power, even under high-acceleration conditions. The reason they did so is that they did not suppress crank tortional flexure. Such vibrations were transmitted directly to the cam via the timing chain and, as a result, the valve event timing was adversely effected and valve bounce was aggravated. All this led to reduction in power, and we are not talking about 0.5 to 1 hp here, but sometimes 12 to 14 hp on a 400-odd-hp engine. The bottom line here is, use a functional damper first and worry about its moment of inertia last. That way your motor will make more horsepower, longer.

[Dave Schiffers]

So in simple english, do I understand this correctly,...
The "crank damper" is one location it's usually not better to go lighter?

and,...
"use a functional damper first"
means use a damper that has some weight(inertia) to be able to
absorb vibrations?

Better to run aluminum rods and lighter pistons if trying to lighten internals?


The help from those far more experienced here is very much appreciated.
Thanks for taking the time.

Thanks,
Dave.

[Steve C.]

Personally over the years I've used aftermarket dambers that were meant to be used on a Pontiac and not something that is adapted. For example I've used two units from BHJ with a part number for Pontiac that fit fine. Another was a custom unit from ATI that also went on with little modification. And for me personally weight was not a factor in my decision as I just presumed that the companies made them compatable for the end use. And, again for me personaly, price is generally not the motivating factor in my choice. But if one is building on a budjet, then a damper from a company like Proffesional Products could well be what you are looking for. Presuming they sell the appropriate unit.
I'd ask or look at the catalogs from vendors that deal with Pontiac specific and see what the sell. Buy what fits and whats within your budjet.

My engines are internally balanced and both the flexplate and damper are neutral balanced and not factored in. Reducing weight on the crankshaft would be like reducing weight on a flywheel. When the piston and rod assembly becomes lighter, the amount of counterbalance mass needed on the crank becomes less and usually by a bigger amount.

[Dave Schiffers]

How do BHJ and Romac compare to each other? Anyone have experience with both?

and

Who sells BHJ Balancers?

Thanks,
Dave

[Steve C.]

Dave, I have no experiance with Romac. Some like BHJ and some don't, I had no issues on my specific builds. But that said, John at the shop has had issues with two of them in two different build ups not involving Pontiac. I had a old one laying around and I recently sent it to BHJ for recertification and any necessary rework at a cost of only $45 and now its like new so I'm going to use it, otherwise I'd buy another unit from ATI.
As far as where we got the BHJ dampers I have no idea as they were ordered thru mu engine builder at the time.