Nitromethane126

I have a 383 that I was running with flat top's and I'm switching to dished pistons, there's about a 15g weight difference between the old pistons and the new pistons (dish pistons are heavier) - should I rebalance the motor or can I get away with just swapping the pistons and getting on with life? It'll be a turbocharged 8000rpm motor putting out 800+hp. Someone told me if you're within 5% of the weight of the old stuff, you don't NEED to rebalance, i've never heard this before, is this true?

I have already heard the replies "you're using expensive parts, you should rebalance" - and "grab a good scale, and grind on your $800 pistons that cost 3 times the price of a machine shop to balance if you **** them up" - I'm not grinding anything! I would like replies from people with balancing experience who can explain to me the con's of not balancing this, excessive bearing wear, damaging vibrations etc. I do not know what balance it was balanced with, it was done by a good local drag race machine shop so I assume it's not 50/50, but I don't have the receipt anymore so don't know what balance it is.

RB83L69

15g is alot. That's about ½ ounce.

Most people that I'd trust on something like that, say 5 grams, not 5%.

Your total rod + piston weight is probably somewhere around 900-1000 g. So your change is in the neighborhood of 1.5 - 2%.

Mostly you'll have vibrations; probably not real serious, since at least all 8 are the same.

You might want to look for some pins that are a little bit lighter, to reduce the difference. If you can get it to within 5 g, I'd say go for it.