Surprise pistons
 

So, currently in the middle of a 355 roller cam build. The base of the build is cleaned up 638 block, 30 over. The deck was skimmed enough to make for a good gasket seal, but not too far from standard 0.025 deck. I bought a balanced rotating assembly with a specific build in mind. I wanted good torque engine with about 9.5:1 compression roughly and reliable. I have since put the short block together and am working on the top end. I’m using fresh Vortec heads with a Comp xr270hr (.495/.502 - 218/224).
The problem comes into play when I noticed my piston to deck height was more than expected. While trying to figure out why, I noticed My rotating assembly did not come with the advertised pistons, but a set of Rebuilder pistons (6cc 4 valve relief) with a shorter compression height. I’m measuring approx 0.038 in the hole. The frustration of this issue is another story, but I’m stuck with what I have.
With this set up (everything new internally), this roller cam, and the vortec’s set to match this cam, what would be your recommendations for a gasket thickness? This build is a street engine, but I’m concerned now for my compression and quench numbers. I would greatly appreciate any advice with the exception of a complete tear down and piston swap.

Re: Surprise pistons
 

The only real option is to install a head and check the valve clearance. Once you know that you can order the thinnest steel shim gasket that keeps valve to piston clearance acceptable. The bad news is that quench is still probably going to be over 50 of not 60 thousandths. With a little playing with Summits filter settings you can look at all the head gaskets by bore and thickness. Depending on the cams cylinder pressure you may get away with that big of a quench and cheap gas. The other option is to pull it apart and get the block decked.
You may end up going with something like MSDs 6 series with electronic timing Control to be able to keep the timing optimized without detonation issues. When your combo is on the edge of detonation is can be really hard to control with the standard HEI distributer. I didnt see the piston material but cast or hypers don't play well with detonation. The last motor I had like that was fine at idle and WOT but tuning for mild acceleration was terrible. It rattled like machine gun fire. Alot really will depend on the quality of your local gas. When I had a tank that rattled to much I would throw some e85 in and that did the trick.

Re: Surprise pistons
 

Just run the thin shim gasket and call it good. I have actually run a lot of quench in a stock 350 and didn't notice anything negative about it. When I took it apart the pistons were over .250 in the hole and it had a .045 gasket on it. The .015 gasket will get you in a decent quench range.