Well, as things go with me, the unusual seems ordinary and Mr. Murphy just wont let up on me.....

Been chasing a vibration problem that started at my first and only drag run at the Dynotech track day at IRP in INDY back in September 2007. The vibe started immediately after the drag run and always was predictable from 2700rpm up.

Replaced numerous parts on the engine, checked fuel pumps, fuel flow, wiring, injectors, valves, distributors, ECM, modules, had the Flywheel, pressure plate and balancer checked,, you name it and I tried it.

So 2-3 weeks ago I pulled the engine and took the Scat 9000 crankshaft that I put in just before the track day , with the Flywheel and PP and damper to the engine shop for a balance check..

They call me up, "larry, we found the problem, the crank is out of balance by 30-grams",,, they ask if the crank and flywheel and PP and damper are the same as when they balanced it, said of course they are...

They scratch their head and tell me they have never seen this before, and I tell them that I have problems that no one has ever seen before as a matter of course.... so I am not surprised.

As far fetched as this sounds, our guess is that the crank flange is twisted enough to throw off the balance, the rods appear to be OK, and the pistons travel to the same height when I index the crank so the mains appear to be but regardless, I told them to throw the crank in the trash and I bought a 4340 Eagle crank and H-Beam rods.

My car only makes 415-rwtq so evidently, the Scat 9000 is not good for that amount of TQ.

Cant explain it, and it hurts to much to think about it... the silver lining is that I now have forged rotating assembly and the vibration will be gone.

The lesson I learned is not to buy parts at the border of what they claim them to be good for.

Quote:

I always recommend people build the best bottom end they can afford, even if they have a specific target HP in mind. Years down the road when you want to do more, you want your rotating assembly to handle it.

-- Joe

You can't always afford a nice bottom end after spending all the money on blue anodized rocker arms and milled valve covers and polished superram plates.

Quote:

haha

When you got ugly engine bays like me you can afford good internal stuff.

Actually, I broke the bank on valve covers in September when my factory fbody covers wouldn't seal anymore. Whole $45 on new ones man..

-- Joe

Like my machine shop said,

"it's OK until its Bad, then its not Good".

It bugs me manufacturers equate strength to HP when TQ seems to be what made it fail.

Also, I spent a lot of time chasing this problem and everyone saying, "no way its the crank".

And besides, I picked up 2 tenths with the shiny Superram cover plate.

Well, I guess you could back-calculate their HP values.

Assume their 400 HP rating applies at 6,000 rpm, that's 350 ft-lbs of torque.

So if your 399 HP motor makes 400 ft-lbs of torque at 3500 rpm, you don't want their parts.

Ouch that sucks.

Very interesting. I'm glad you finally got it chased down.

RACE ON!!!

Wow! Lots of sleuthing, glad you found it. Good luck.

Thanks guys,,, it was an expensive debug for sure, I pray that I never have to chase another vibration problem....

Many people said they thought it was a miss related to spark or valves or fuel, and it could have been, but is tyurned out that it was not.