Fast3rdGen

I know people always have their rotating assy's balanced, I did with my 383. But I have been hearing alot of debate about it for basically stock-mild rebuilds. I have a 96 vortech 350 that I am going to be rebuilding. Over at camaroz28.com, quite a few guys have mentioned that a rebalance is not necessary when changing to a lighter piston. Well, the vortech has heavy cast pistons and I will be going .030 over with lighter Hyperuetectic "stock replacement" flat top pistons. This is on a street car that might see some light to light blasting, but no strip time, I'm just bored with drag racing anymore. Thoughts? Balance or no?

jtrescot

If the parts involved are already at the machine shop I would have it done.

Bigseth

iTrader: (11)

I know you can use the H345Np speed pros. Machine shops order them all the time to go back in those vortec 350s. But if you have the money and its at a shop go ahead and have it balanced.

Seth

ljnowell

Low RPM daily driver engine? No it doenst need to be balanced. An engine like that doesnt need to be perfect, just perfect enough to run. However, if I had the cash to have it done, I would.

Damon

If the difference in piston weight is less than 5%, you can definitely get away without it. If it's less than 10% you can often get away with it, but a balance job would be advisable if only for smooth operation and long life. It it's greater than 10% you need a rebalance.

Above are rules I use and follow myself in my own engines. Budget STREET engines that do most of their life tooling around town with only the occasional trip to the strip. Not race engines.

DON'T forget to take the weight of the wrist pin into account. Some are very "thick wall" pins and weigh considerably more. I don't count the rings if they are all the same thickness. If the wrist pin is typical (~145g) and the rings are the same thickness you can compare just on piston weight alone. If not, you have to factor in the differences in wrist pins and rings.

Example:

Stock pistons are, say, 550g each. A 5% factor would be 28g more or less than that. Assumes both sets of pistons have the same weight wrist pin and same thickness rings.

I HIGHLY recommend you get a cheap digital postal scale capable of measuring in grams. Trying to figure this stuff out from specs or guessing at it is worthless. You must KNOW what everything weighs if you're going to play the game of "is this close enough I can get away with it?"

I absolutely guarantee you I know EXACTLY what my reciprocating components weigh before I decide on whether a balance job is needed or not. Deciding what you can get away with is a tough decision even if you know all the facts. Without the facts you might as well pony up the bucks and pay the money for a rebalance to be sure.