InsomZ

iTrader: (1)

I'm thinking about doing the Cometic 0.040 Head Gaskets when i do the g5x3 install and LT headers.

I have done a search.. still can't figure out what that would bump the compression ratio to?

would it be safe? shouldn't affect Piston to valve cleareance right?

this is for a 2001 z06 .. thanks!

InsomZ

iTrader: (1)

anyone know?

ArKay99

iTrader: (1)

The 2001 LS6 MLS gaskets are rated at .060" crushed thickness. So it would in effect amount to milling the heads ~.020". That comes to around -3.67cc's. On stock LS6 heads I would think around 10.9:1 to 11:1 A potential problem may exist though. Most LS6's have the pistons out of the hole ~.008" and this would reduce you quench to .032". This is tighter than most recommendations which is .035"-.040". It would be best to pull the heads, measure your deck clearance and purchase the correct gasket when the deck height is known. The question as to whether this would affect piston to valve clearance can be answered as a yes it will. Whether it will put p/v too close you will probably have to measure. The G5X3 cam fits stock setups when run at a 114lsa, but the 112lsa version is too close. At least that is what I have read. You may be able degree the cam to get it to fit, but you may also retard the cam out of some of it's power. You MAY want to look at the Cometic .045" gasket as that will still bump your compression and keep your quench distance within limits.

InsomZ

iTrader: (1)

cool i'd do the the safer one then.. .045" that should still bump it to what 10.5:1 compression?

i don't want to have the heads pulled yet.. just gonna get the cam and headers put on.. do heads later. i figured while i'm getting the headers put on.. might as well bump the compression a little worth maybe what 5/10rwhp more?

ArKay99

iTrader: (1)

-.015" will give you around 10.7:1 on an LS6, around 10.4:1 on an LS1. ~+5hp. Nothing you would feel. I would be more worried about P/V with that gasket and head/cam combo than the extra 5hp. You may have to cut the pistons a little and that would lower your compression slightly. If the G5X3 has .085" intake clearance and you put the valves .015" closer you will only have .070" intake p/v. I'm not saying this is what you will get, no one could be sure. You would have to measure it.

InsomZ

iTrader: (1)

thanks man.. very informative. i appreciate it!

ArKay99

iTrader: (1)

NP. I'm hoping you will get some other input on this also. I don't have experience with the G5X3 being used in your situation. I just did a set of AFR 205's and a 224/228 .581"/.588" on a 112. I used the .040" cometic gaskets because the pistons were out the hole ~.004". I also had the heads milled .010". I'm at about 10.8:1 now and will be pulling the heads and cutting them another .020". I know I can do this because I measured my p/v, and my deck height, and came up with enough clearance to go to 11.2:1.

DanZ28

iTrader: (5)

Don't have anything to add, but this is informative. What's the formula for figuring you CR and the quench area?

InsomZ

iTrader: (1)

ok so .. if its safe to assume.. .085" intake clearance w/ the G5x3 and .045" gaskets reduce that to .070" intake clearance.. how much clearance is considered safe?

ArKay99

iTrader: (1)

At the top of this category is a sticky with a CR table in it that was compiled by Tin Indian. It is accurate enough for the purposes of this thread. I am talking about quench height or distance in regard to the head gasket and how the gasket thickness can affect that parameter. I am glad I am being informative but I am in no means an expert in this area. I am merely forwarding my understanding of what this is regarding an LS1-LS6 and offering the benefit of my experience with a couple of h/c installs. I was hoping there would be more input on this from others.

DanZ28

iTrader: (5)

Give it some time, more people will chime in.

I think .075-.080" is considered minimum clearance. If you float a valve just once, in your in for some major repair if you don't have proper clearance.

I to am trying to figure out my exact CR and Quench. Not to steal the thread, but how would you calculculte this:

.005 off the deck...Flat top pistons +.008 (below deck) with -2cc releifs...3.905 bore...heads milled .035"...Cometic .040" gasket...Did I miss anything? I'll do more research as well.

Thanks,
Dan

DanZ28

iTrader: (5)

To answer my own question, looks like I'm approximately 10.75 CR and a .048"quench. I think I screwed myself with a .040 gasket, should of went .030" to get a .038" quench

Dan

DanZ28

iTrader: (5)

BTW, by my calcultion, you would be 11.0 CR with a .040 gasket and 10.88 CR with a .045" gasket. Like was stated above, you probably wouldn't want to go thinner than a .045" gasket to keep your quench down to a .037".

Damn amazing what info you can find on this site sometimes

Thanks,
Dan

ArKay99

iTrader: (1)

I'm sorry if I led you to believe that the G5X3 cam will give you .085" of p/v clearance with a stock MLS gasket. The truth is, noone can predict what the clearance will be in your car. You will need to measure it. I was only offering those numbers as an example.
The safe clearance has to do with the valves, the pistons, the connecting rods, and how fast you plan on spinning the motor. For a stock bottom end LS6 with stock valves and running to ~6800-7000rpm I have read minimum is .080" on the intake and .100" on the exhaust.