JRP did you account for the valve relief? If so then what's the ratio without?

Thanks!

 

yes, i accounted for a 1cc valve relief, my calculations with a flat top are 11.8459983818688

 

Here's my thoughts..
If u look at most AFR setups most guys seem to run them at 62CC and they run .045 which gives u a desirable quench/cr...Now I'd like to see PP/TEA/PRC's running 62CC and a cometic .045 the LSX/90 TB and all the other goodies back to back against the AFR's...

Most guys dont,they throw on these companies heads alonhg with GM gaskets,a basic PTB,cheaper headers,pulley etc...I wonder,how much better the AFR really is vs the others with the same parts..

No one has done that test,Put a stock LS6 shortblock on a engine dyno with the SAME PARTS and compare all the heads....Then we could see if its worth 5RW/10/20??????

I wonder,I really do.....

 

11.0, 11.1, 11.2 compression is nothing new, guys have been running that long before the AFR's came out. cometic gasket use wasnt as prevelant prior to the AFR's imo but quench isnt gonna account for the disparity in hp variances seen with afrs vs others. also not every afr combo is running a 90/90, there are plenty of results with ls6 intakes and stock ported tb's, hooker long tubes, ect. evenn guys who dont follow tony's recommendatitons of milling and cometic are putting out some above average numbers.

 

So back to the reliability of cometics vs stock head gaskets...

 

Yes but it would be good just to see a TEA 5.3 S2 62CC VS a AFR 205 62CC with the same shortblock and other parts to run...Then u could see what there really worth,I'd love to see that test.....Wouldnt u???

 

In my calculations I don't use negative values. It doesn't make any sense for a distance between the top of the piston and the top of the combustion chamber to be negative.

Actual deck height is measured this way. If it's .006 or .008 then that's how far the distance is, but who knows what those numbers are actually referring to (could be piston out of the hole, or recessed in the hole so I might be wrong in using them).

I could care less about piston out of the hole for my calculations, and I've went over that plenty of times in other threads. Best way is to actually measure the deck height and not piston out of the hole, because honestly, piston out of the hole doesn't help with any calculation I've ever used in determining the clearance volume. If anything, the piston protrudes x, which cuts into the clearance volume; it doesn't make it negative.

 

THANK YOU! lol

 

oh, i'd love to see it, but it wont happen. i'd be more interested in the excuse some of the cheerleaders would come up with after seeing whatever the results may be

i'd rather see an engine masters type **** where packages could be put together showing the potential of said heads.

 

tq them down properly, heat cycle, retorque, and your good.

im running the .045 cometic myself.

 

Dude your not getting it-if the piston is out of the hole you get - deck height, which means the piston is closer to the head which means your compression will rise. You have to account for the piston and all stock LS1's LS6's pistons stick out of the hole.

 

What are some steps I can take to reduce the chance of leakage with the Cometics?

 

I know the piston sticks out of the hole. What you say is true. If the piston is closer to the head, the compression will increase. But, the formula I use then ends up being negative if I put a negative value in. Maybe it doesn't matter, but how can a clearance volume be negative in the real world? Looks great on paper, but how can the piston be taking up negative space in the area between it and the head? As the piston comes out of the hole, it will shrink that volume, but there has to be room between the piston and the head, correct? The formula *seems* to find the volume in inches.

Clearance volume = 0.7853982 x 3.898^2 x -0.008 = -0.09546926

You know, the more I look at this, the more I think this formula is inaccurate for finding the deck height on the LS1. It was designed for the SBC, and I've been looking over things and I don't see where the SBC ever had a piston come out of the hole. So, the formula or constant in the formula may need to be modified to account for this.

Either way with 93 octane and a tune and the G5X3-114 and AFR 205 59cc with either .040 or .045 cometics will run without incident and are worth it, and that's what this thread is about.

 

I understand your theory, but when using compression calculators, you have to be able to determine if the piston is above or below deck. Math dosen't know if your piston is above or below deck. Like you said, the old calculators, like the Ross compression calculator, do not read "above deck". This is because most old SBC's were always below deck. The only calculator that I have found that utilizes above deck is the RB racing calculator that I have tried to get everyone to swap to. It explains which values need to be entered and wether or not to make them a negative or positive figure. By there instructions, pistons sticking above beck are negative. When you look at the piston volume, it says to enter a positve cc for a dish, which could equate to below deck, and a negative cc if you have a dome, which could equate "above deck". If it's right, you can't argue with it. You'll just end up confusing yourself and maybe a few others if you don't. http://www.rbracing-rsr.com/compstaticcalc.html

 

.045 Cometic with AFR's 60.6cc, milled .040!! No detonation or leaks!

 

Im so damn confused about this crap.....maybe indecisive is the better word.

 

Hey, I'll tell you what I decided. I'm going with stock metal gaskets.

Why?
- WAY cheaper, and H/C has stressed the budget for sure.
- While it seems debatable here they seem to be a lesser risk of leaking.
- So lets say you decide later on you want to bump the compression even more, you can add the cometic and do it. Going stock now allows you some easy mod potential.

 

Sounds like a sound strategy to me!

 

I'll second that!

 

FWIW the OEM metal gaskets are.060 and the OEM graphite are .053.