What is my compression ratio (static)?

Doc99SS · 07-02-2009, 03:51 PM

I have a 402 from Texas-Speed with -10cc pistons and 64cc chambers.

How much "down in the hole" is the piston at TDC, and how much volume would that displace? Lets call this Vdh.

Also, I need the volume of the head gasket. Lets call this Vhg. I do not recall the thickness.

So far I have:

CR = [825 + 10 + 64] / [10 + 64] = 12.15 which is way to high.

However, I need the following:

CR = [825 + 10 + 64 + Vdh + Vhg] / [10 + 64 + Vdh + Vhg] to accurately calculate the static compression ratio.

Doc99SS · 07-02-2009, 04:14 PM

I estimate the compressed head gasket volume at 7.2 cc if the compressed gasket gauge is 0.035". What do you guys think?

KCS · 07-02-2009, 08:57 PM

I got 10.88:1 CR assuming:

4.005" bore and 4.00" stroke (825.91cc)
4.030" x .051" gasket (10.66cc)
.005" out of the hole (-1.03cc)
64cc chamber
10cc dished piston

Doc99SS · 07-03-2009, 08:13 AM

So these LSxs are "out of the hole", not "down in the hole" 0.025" like the SBCs?

Thank you for the reply.

KCS · 07-03-2009, 09:57 AM

Typically they are out of the hole ~.007" stock. TSP seems to use GM MLS gaskets on their longblocks, which are .051" thick, so I am assuming they do the same. You should have a build sheet that came with your engine to tell you all of this, or TSP may have it on record for you if you contact them.

Doc99SS · 07-03-2009, 03:05 PM

I have TSPs build sheet for this short block. Being a short block, there is no mention of head gasket thickness. I can not remember what I used, but they were highly recommended at the time, which is now 2 years ago.

KCS: I believe that you have given me the missing volumes. Thank you.