340 Piston Selection

Ok i will admit that i have not done the whole math thing on this ,but we are both in kind of the same boat and i did some research on this years ago before i took along break from this so my math is not great on this and i have not figured out if the valvepockets would end up being a problem in this case,the only real difference here is that i havre fresh.030 bore and a somewhat similar cam bit mine is a roller.

Your heads will probably not be 65CC anymore when the headportingshop is done with them,they will probably be alitle bigger.

I would not go with a popuppiston that sits above the deck for a whole bunch of reasons.

I would do a zero deck flattoppiston and cut the heads until i get the desired compresion.

I have read in the past that RPM340 heads are supposed to be possible to cut until they are closedchamber without isues and at that point they will be closer to 55CC but i have not done the math on this,and at that point you will have ended up needing to cut the intakeface of the head aswell a bunch to make any intake fit again,this is just what i have read,i have not measured or calculated this and can not say for sure if this is correct.

Another problem that may show up at this point after cutting the heads 0.060" or so is that the valvepockets in the pistons may not be deep enough anymore but i cant say for sure.

Sure you could get there with either a set of those heavy TRW/Speedpro/SealedPower #L2316 whatever they may be named nowadays pistons or a custom popup piston but at that point if you want to upgrade your heads at any point in time in the future you are screwed again and need to change pistons or go for a ridicilusly thick headgasket.

The other option is some kind of domepiston and at that point you have either ancient TRWL2322 pistons with huge domes (if you can find a set,they show up from time to time for sale brand new )that fits a stock head but will not fit a edelbrock chamber im sure those domes can be reshaped to fit a Edelbrock head since they can be cut down to flattops but i bet its a ton of work to get right and you are once again stuck with a popuppiston that wont fit any other heads except open chamber garbage. Ross makes an of the shelf dome piston aswell(atleast in .030 over)but once again its made for a stock head and the dome wont fit an edelbrock chamber,they may be possible to cut and reshape to fit your heads but who knows. They TRW L2322 piston is quite heavy but not as heavy as a L2316 piston,the ross domepistons are a bunch lighter

I think i have read that Diamond might have done domepistons for RPM340 heads but i have not seen them in the catalog.

This is the reality of pistons for the 340RPM heads its nothing wrong with the head itself its a rpm head but the whole option of that openchambercut makes them a damn headache to anyone who wants to do something hotter with them than bolting them to a stock shortblock and have fun. I have a very well ported set ontop of a 345cui shortblock in my garage and i regret not getting the closedchamber version everytime i look at them it was a damn stupid mistake.
The thing is that you will end up having to cut quite alot to make them closed chamber and get some kind of squish/quench or whatever you like to call it.

There are other opinions in this thread and i think more people could have more and better opinions and possibly options,but i would not go for another popup piston build,i would certainly go for a zerodeck flattop and cut the heads until compression is where it needs to be,and possibly cut deaper valvenotches,im not sure about that part.

Darn it,i was wrong on Mahle,found the place where i saw .040 over pistons for a stockstroke 340 and they where made by SRP