Hello,

I've just torn down my 402 and I'm excited about rebuilding it and putting it in my 70 Chevelle. The pistons in it now are TRW's with 13:1 compression. The engine has a bore of 4.125" and stroke of 3.760", the heads are 119cc. I'm looking for 10.25:1 compression ratio and am looking for a set of pistons to buy. Jegs and Summit don't have anything but JE 8.1:1's. I've called JE and Wiseco but all they can do is sell me a custom set for $100-125 per piston. Has anyone out there experienced this and found any supplier that has off the shelf pistons with a compression ratio close to what I want? I appreciate the help. Thanks.
Patrick Bellene

your not going to find a stock replacememnt 10.25 piston with a open chamber head because the 10.25 compression motor ran closed chamber heads. I saw once that SRP sold some 10.25 pistos to work with the open chamber heads but have looked for them myself and could`nt find them. Another option is if your TRW`s are in good shape, have a machine shop mill the dome down to give you the copmression ratio you want. Most hi-po machine shops should be able to do this and would be able to figure out how much to take off. One other option is to use the 10.5-11.to1 closed chamber piston with the 106cc chanber and run them with your open chamber heads. you will be around 9.5 to 1 or so but it`s enough compression to make a good street motor.

The correct 402 piston is a TRW L2354. These have a .180 dome (19.8CC) but only yield about 9.3/1 with a 106CC head and a paltry 8.5/1 with open chambers. The bigger piston is the 11.0/1 TRW comes in around 33CC. With the smaller bore of the 402 motor the domes may clear the open chamber heads, but you will have to check. I run the L2354-030 with .014 deck, .039 gasket in there now and 290's CC'd at 104CC for 9.5/1 CR. Hard to build compression on these with out thinking it through - cutting the deck, milling the heads and/or piston domes depending on what you start with.

you can still get the 11 to 1 pistons for the 375 hp 396. these can be used with your open chambered heads the 375 hp 396 pistons have a 38 cc dome. and even with undecked blocks they provide a very good deck height around the .015 area. speed pro still sells them for 351 bucks. you can run the numbers and play with the compression ratio on these.

these will give ya what your looking for. keep the deck height in order and play with gasket thickness. also on open chambered heads when you shave .015" you take 2cc off the chamber. so you can play with this as well to get the numbers your looking for.

remember as well if you have any head work done like new bigger valves install this reduces the chamber as well. before you know it those 119 cc rated heads end up around 114 cc. and you really havnt done nothing with them.

10.29 to 1 is what i came up with using prestage.com

4.125 bore
3.76 stroke
.015 deck
.020 gasket steel shim
119cc heads
38 cc dome 375hp 396 pistons.

so you can get what your looking for.

trw-L2242f30

Thanks for the help guys. Any idea if I would have better options available to me if I bored it out to 4.155"? Also, are there interference problems with using a closed chamber piston with an open chamber head, or is it the other way around? Or does it just reduce compression ratio? Thanks for the help.
Patrick Bellene

We just built a 402 with open chamber heads(119 cc's) using either .319 or .340 dome (can't remember,but the part # that ddeennis posted sounds familiar)..ended up around 10.2 ot 1 or so

The interference occurs near the exhaust side of the Comb chamber (closed piston w/ open head). But on a 4.125 bore, you may not have any interference because of the overall smaller piston size. Even if you do, it is a small fix with a die grinder in the comb chamber. Really not a drastic issue, just something to be aware of - don't just bolt on a set of heads without laying some clay on top of the pistons and checking for clearance. Certainly not the issue to deal with of attempting to install a closed chamber head on a "true" open chamber design piston will cause.

I HAVE A NICE SET OF TRW PART# L2354 STD BORE OUT OF A 71 CHEVELLE.. THEY ARE USED BUT ARE IN GOOD SHAPE TAKE $100.00 IF INTERESTED CALL 918 527 9426 THANKS :thumbsup:

Hello,

I've just torn down my 402 and I'm excited about rebuilding it and putting it in my 70 Chevelle. The pistons in it now are TRW's with 13:1 compression. The engine has a bore of 4.125" and stroke of 3.760", the heads are 119cc. I'm looking for 10.25:1 compression ratio and am looking for a set of pistons to buy. Jegs and Summit don't have anything but JE 8.1:1's. I've called JE and Wiseco but all they can do is sell me a custom set for $100-125 per piston. Has anyone out there experienced this and found any supplier that has off the shelf pistons with a compression ratio close to what I want? I appreciate the help. Thanks.
Patrick Bellene

Myself, Mike or Chris can get you a set of Probe 2618 Forged pistons. PM one of us for further details and to figure out compression

They are 30cc dome

They are available in 4.125" and 4.155", Soon to be available in 4.185" bore

They use 1/16" 1/16" 3/16" rings

What is your deck clearance, head gasket bore and head gasket thickness ??

Hey Butch ,note the date of this post.
I started to answer it too before I realized it's 5 years old.

Hey Butch ,note the date of this post.
I started to answer it too before I realized it's 5 years old.

Mike, Thanks !!!

:o:o I didnt see that until now

I wish there was a way to keep from bringing dead posts TTT 5 years after the last post.

would you like to sell thoes 13.5:1 pistons i need a set for my dirt modified? If so please send me an email cmh242@yahoo.com