my crank is balanced for 1567 b.w. My piston and rods B.w. come out to 1528. So the B.W. on the crank is 39 grams heavier. In the last few hours I've just done some reading and they said over balance can be good for high rpm vibrations??? Can anyone else back this up?

It didn't say how much over balance though.. Is this too much?

How accurately did you weigh the big ends and the small end? What type of scale? Also, they use a special fixture to suspend the one end while they weigh the other. If it was balanced and run before and given it's a nascar motor why are you doubting it?

Also, how do you know that was the bob weight it was balanced for? I've seen many cranks that were re-balanced and you can't go by stampings that might be on them.

Rods are blueprinted. They came with specs on big an little ends.

Crank is also blueprinted from Arrington.

I just wanted to double check everything, as this is the most I have ever stuck into an engine. Doesn't hurt to double and triple check, and I'm learning more by asking these dumb questions

Yes a Overbalance is common and Prefered. Its been dyno tested and proven that it can help with HP.

IMO the slight overbalance gives the crank a slight Flywheel effect that helps offset the compression and vacuum pull forces against the piston that it will see. mike

That brings up a question.

How about under balance? I have a light assembly that I run NA. Looking to change it a little when I freshen it up. Maybe a little stronger rod, currently running a GRP series 2000 with 3/8" rod bolts. Would possibly move up to a 7/16" for longevity with nitrous. The pistons will get some other changes like moving the rings down, and a small dish. Just depends on what Ron at Diamond suggest.

Of course if I can't find a reasonable 60mm cam core to make the nitrous lobes and seperation I want then there is no sense in doing any of this.

Really hate to screw with the engine at all as it would be an awesome peice for someone running NA in a single carb cast intake class. It will be next year at the earliest before I do anything. House and garage building comes first then play that's what the wife says.

Leon

I dont like the idea of any under balance myself for the reasons stated above. But thats just MO.

In R5P7,s thread "Hey 40Ford Need some Info" he gives a link to Speedtalk. Go take a read,

Some of the guys/builders are in favor of a underbalance. Others a perfect 0 balance, and yet others a 1% to 3% overbalance.

Im in the Slight overbalance camp. mike