I've been trying to figure out the volume of the valve reliefs and I can't find it anywhere. However using this static compression ratio calculator http://www.rbracing-rsr.com/compstaticcalc.html if I put in all the other variables I get 6cc. The reason I ask is I'm trying to figure out the compression I'll be at after switching head gaskets during my heads/cam swap.

 

I think they are 7cc's total.

 

I've also seen people claim 4.5cc or 8cc. I'm just going to go with 6cc since that works if I put alll the other known variables into the calculator.

 

Difference is likely valve reliefs vs. valve reliefs AND area above top ring.

 

I get 6cc playing with the calculator like this:

I have a ZZ4, which uses the LT1 pistons and comes with 10:1 compression

Bore: 4"
Stroke: 3.48"
Deck height: .025 (all gen I/gen II engines "stock" deck height)
Compressed thickness: .051
Piston Volume: 6cc
Combustion Chamber: 58cc
This calculator assumes that your gasket bore size is the same as that of your cylinders.

It comes up as 9.99, which is pretty much 10:1. I'm just making sure that when I switch to the GMPP .028 gaskets that my CR will be 10.56:1.

 

While iw as putting my engine together, I got some silly putty from the toy section at the drug store and mashed it into the valve reliefs then too a razor blade and scraped it level with the piston top. I dug the putty out and pushed it into a medicine dose tube (like a small test tube) and came up with about 4.5 cc. Crude, but it works!

 

pretty sure it's 8cc

 

So far in this thread alone we've heard 4.5, 6, 7, and 8.

 

4.00" bore
3.48" stroke
58cc chamber
.051" x 4.160" gasket
.025" down from deck


Would need 12cc relief piston to make 10.4 compression which is stock...

 

Chamber isn't 58 cc, it's 54

 

LT4 heads are 54

LT1's are 58 totally stock with .006" removal per cc on decking. I just cc'd a couple last week.

 

Just going off the last set I measured a couple weeks ago, so like I said above he needs to cc his heads to make sure, 4cc will make a big difference.

 

did anyone else beside LT1inaMG actually measure their piston reliefs? I will be pulling the heads in a bit and will measure on my own which is the only way to be sure. I find it retarded how people plug values into a compression calculator to determine what the relief size must be maybe this is where the 58cc combustion chamber comes from. Well in order to get 10.4 it must be x. Blueprints and actually post castings differ as well as where the parts were produced/variances/quality of materials etc but not by as much as 4cc's. I will post my findings.

 

M1,
The 1st set I pulled off of an untouched LT1 were presumed to be 58 and went to the porter with that *** umption. Cam and pistons were ordered on that assumption and block "0" decked.
When the heads came back I CC'ed them and they were 53.2, needless to say I spent some time redoing the chambers (and not mess up the porters work)to 56.4 and let it go on pump gas with 11.? static compression,almost 12-1. It ran fine with no problems.

I have CC'ed ALL the rest before doing any work.