I need to change out my pistons to raise compression to 10.5:1 There stock rite now and motor has hardley even been ran can. My question is can i just change out the piston and use the same rings? Or do i need to rebalance everthing? I put a roller solid cam with a .680 lift I left the botton end the same with the 4" stroke. Did some head work, bigger valves ported and polished oval open chamber heads with 106cc. Its a gen v motor and i have a multi port injection that im going to put on it. Any insight would be much appreciated thanks.


BIG BLOCK :bowtie: TILL I DIE

I wouldn't expect just the rings to affect the balance dramatically, but since you have to pull the old piston/rod combo and put everything back together, it doesn't make much sense not to check things while you have them apart, especially since you have put time and effort into getting it right. JMO.

i'd draw the line at about 10-15 grams max per piston/ring/pin combo as the limit. if the newer dome pistons are different more than that,, i'd rebalance. you can get by otherwise. hope it helps.
andy

edit: oh,, if you had to go to a taperwall pin to reduce a bit of weight,, you can do that safe enough.

Yes that really helped out thanks!!!

i'd draw the line at about 10-15 grams max per piston/ring/pin combo as the limit. if the newer dome pistons are different more than that,, i'd rebalance. you can get by otherwise. hope it helps.
andy

edit: oh,, if you had to go to a taperwall pin to reduce a bit of weight,, you can do that safe enough.


Should i reuse my rings or replace them with new ones and can i do that without hoening the block. Im jsut trying to change the pistons without having to put a bunch of money into the motor. You said no more than 10-15 grams does anyone now what a set of stock gen v 454 pistons way?

Get a cheap digital postal scale (one that reads in grams) from Staples and weigh them yourself. That's what I do. No guessing involved then. And don't take the piston manufacturer's word for it what they weigh. Their specs are often wrong.

To have a chance at getting the weight close you want hollow dome pistons. They are recessed on the bottom about the same amount as the dome on top, so their weight is usually reasonably close to a stock flattop piston. Solid dome pistons are like a flattop piston PLUS a dome on top and won't stand much of a chance of being close in weight.

I wouldn't reuse rings, but if yours are fresh (and the right width to work with your new pistons' ring grooves) then yes, you can reuse them on a very low-buck effort. Pleas note that in the early 90s GM started using metric rings in many of their engines (certainly in the small block, not sure in a big block). If that's the case you won't find an aftermarket high performance piston designed to work with metric rings and you'll have to buy new ones.

And if you overbore the engine then you need new rings, period.

agree with damon, i use an old paint scale that reads grams and can be digitally zero'd. also recently got a cheapy 20$ harbor freight one like mentioned ^^. haven't tried it yet though.

rings will wear to the ring lands so,, if they have alot of miles on them,, or you can feel any wear lip in the bores at all,, i'd replace the rings too. they'd work in a pinch,, but,, i'd hate to risk it being the major sealing part and all.
andy

Dude you guys are great help thanks again.

Who i almost forgot my stock rods are probably press fit so does that mean i need a press fit piston?

Yes, unless you want to get your rods modified for full floating wrist pins.

Na i would rather buy new ones.

full foating means that you can change them yourself with no press. clips hold the pins in. you can buy the new rods for either way. press fit or floated. all he's saying^^^.
andy

Ya i know about the full float pins i would just rather buy floating pins than have the stock pressed ones machined.

You have the scratch for new rods but you don't want to spring for a new set of rings?

Pressing a set of pins on and off will only run you a few bucks. Pistons designed for full floating pins can be used in a press fit application, but not the other way around.

Well the rods i can use on other builds the rings i cant. Plust the rings are in really good shape look hardly used.

OK, but now you're introducing a SECOND variable that can affect the balance of the engine, plus making sure the clearances on the new rods are right (which you already know they are with the original rods).

Getting a set of stock press-fit rods machined for full-floating isn't expensive. It's an oiling hole and honing a few thou on the small end so the pin can float through it instead of being held tightly.

On a low buck effort it's almost always preferable to keep rotating assemblies working as a matched set. Too many changes and the project often starts to "snowball".

Ya your rite i can just have them set it up for bushed and then keep that set and just change the pistons out. I have to wait till tomorrow to go the machine shop and have them prees out the rod so i can weigh it. Ill see what they charge hes a buddy of mine that helps.

Alright weighed my piston, rod and pin. Piston=647 rod=884 pin=150. All in grams of course, does that sound about rite?