Ok, so I'm looking at buying a built shortblock from another member on here, my question is I already have a set of patriot 59cc 243 heads i was gonna use on my lq4. If I post the spec of the new possible shortblock can someone help me figure out the compression ratio with optional head gasket thicknesses? I tried using the summit calculator but I think I'm entering in something wrong.

3.905 bore
3.622 stroke stock ls1 crank
6.125 Manley rods
59cc patriot 243 heads
-9cc inverted dome dish including valve reliefs
.005 out of the hole
.054 or .040 or .030 head gaskets?
no cam selected yet

I've heard people talk about quench but I'm honestly not sure what that means, I wanted to be around 11.1:1 because this is going to be an n/a street motor but I know that probly won't be the case due to the dish pistons. Any info or help is much appreciated.

 

I come up with 10.23 cr with a .040" head gasket.

 

Quench is very important. If you do a google search, you find some excellent articles on the subject.

It's essentially how close the piston comes to the surface of the head. It's kind of a dead space. As the piston comes near TDC, it pushes air/fuel mixture in to the combustion chamber.

Too much Space ther and the engine becomes inefficient and tends to knock and ping, which will kill the engine pretty quick. Too little space and the piston will contact the head at high rpm's. Get it just right and the engine will make more power more efficiently.

Most pro builders say .040" is perfect. Some people here say you can go as low as .035" on an LS engine.

Pick the head gasket that will give you the quench that you're after. NEVER use the head gasket to adjust static compression. Accurate quench is far more important than the small amount of compression change.

For your engine, an .040" gasket is the absolute bare minimum thickness, and you'd better hope you measured each hole with absolute accuracy. If one of those pistons is .007 out of the hole, you could be in trouble.

 

Ok that makes sense, I'll try to search on how to figure out the quench and what's ideal for my setup. I appreciate the info. And yea I kept coming up with that compression ratio also, looks like I'll have to figure out another piston option to get the 11-11.5 compression I wanted for this motor.

 

Just a quick update, I checked with the engine builder and got exact numbers for the deck clearance and other #'s and looks like I'll be around 10.5:1 with a .035 quench area that's ideal from what I've read after your guys info and advice so I think I'll be happy with it, it's not the 11-11.5:1 comp ratio I originally set out to achieve but that should still be plenty for a fun street motor.

3.905 bore
3.622 stroke
9cc dish
.006 deck clearance
.041, 3.910 head gasket
59cc head
10.49:1 comp

now I just gotta get a custom specd cam for my build lol

 

without the 9cc dish in the pistons you would be where you want to be