Compression?
Pro
Joined: Jul 2000
Posts: 590
Likes: 1
From: Suffolk New York
Look for a SCR/DCR Calculator. I posted some links to LS1tech for the excel spreadsheet.
If you mill heads to get 60cc and use .045 compressed head gasket you"ll et around 11.5:1 , but you need to look at your DCR and it's influneced by the LSA and ICL of your cam.
If you just use .040 gasket, you'll net about .5 in compression. 10.99:1
I'm having a little trouble deciding what the "right" input parameters are: like the stock compressed gasket height and how far a pistion sticks up over the block deck.
I'm currently looking at these options myself, along with P&P the heads.
If you have them off now is the time to think about these things, I'm doing it after the fact! Kicking myself in the butt, too!
If you mill heads to get 60cc and use .045 compressed head gasket you"ll et around 11.5:1 , but you need to look at your DCR and it's influneced by the LSA and ICL of your cam.
If you just use .040 gasket, you'll net about .5 in compression. 10.99:1
I'm having a little trouble deciding what the "right" input parameters are: like the stock compressed gasket height and how far a pistion sticks up over the block deck.
I'm currently looking at these options myself, along with P&P the heads.
If you have them off now is the time to think about these things, I'm doing it after the fact! Kicking myself in the butt, too!
Last edited by cam99; Oct 9, 2007 at 07:45 PM.
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
With the G5X4 cam...you should already be considering flycutting your pistons...yes, even with stock heads and gasket.
If you measured your p/v clearance right now, you will probably find the intake valve is only about .040-,050" shy of actually hitting the piston.
Yes, "it clears" (tuners love to word it that way when selling big cams) but not by enough...You are already below the generally considered "safe" p/v clearances of .080" intake .100" exhaust.
So, unless you want to notch your pistons, I'd recommend nothing thinner than the stock gasket.
I'm running the G5X4, and bumped my compression way up by using milled heads and a .040" gasket. But I cut .100" more valve clearance into the pistons to make it work.
If you measured your p/v clearance right now, you will probably find the intake valve is only about .040-,050" shy of actually hitting the piston.
Yes, "it clears" (tuners love to word it that way when selling big cams) but not by enough...You are already below the generally considered "safe" p/v clearances of .080" intake .100" exhaust.
So, unless you want to notch your pistons, I'd recommend nothing thinner than the stock gasket.
I'm running the G5X4, and bumped my compression way up by using milled heads and a .040" gasket. But I cut .100" more valve clearance into the pistons to make it work.
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
I cut mine .100" deep for the intake, and ended up with .090" p/v clearance on the intake valve . Did not have to cut for the exhaust valve, had lots of clearance.
I have milled heads though...you could get by with less of a notch....080" deep would probably suffice. The more you cut from the piston, the more compression you lose...but at the same time, if you're gonna bother cutting, may as well make the room and leave your options open in case you change the setup later.
If you use a .040" thick gasket, with stock (unmilled) 64cc LS6 heads, and assuming 1cc cut out of the pistons, it will bring your SCR to approx 10.9, and DCR to about 8.1.
I would not suggest running a gasket thinner than .040".
If you wanted to further up the compression, getting the heads milled would be the thing to do.
I have milled heads though...you could get by with less of a notch....080" deep would probably suffice. The more you cut from the piston, the more compression you lose...but at the same time, if you're gonna bother cutting, may as well make the room and leave your options open in case you change the setup later.
If you use a .040" thick gasket, with stock (unmilled) 64cc LS6 heads, and assuming 1cc cut out of the pistons, it will bring your SCR to approx 10.9, and DCR to about 8.1.
I would not suggest running a gasket thinner than .040".
If you wanted to further up the compression, getting the heads milled would be the thing to do.
Last edited by Y2Kvert4me; Oct 10, 2007 at 07:19 PM.
