243 Heads Compression Ratio w/ .040 Head Gasket
10-22-2012, 05:10 PM
#1
243 Heads Compression Ratio w/ .040 Head Gasket Had a quick question on what my static compression ration will be with on a stock bottom end ls1 with 243 heads non milled with a .040 mls head gasket? I've done a couple of calculators, and I keep getting around 10.95 to 1, but a guy at tsp said 10.8? Also, is the .5 or .3 difference worth any power besides maybe 5 ponies? Thanks in advance.
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10-22-2012, 06:03 PM
#3
Yea higher compression usually makes better torque on low end as well as higher hp on the top end with correct timing...I'm running the same heads and gaskets and you can tell there is more compression by sound and the fact the coolant heats up considerably faster...
10-22-2012, 06:24 PM
#4
Cool,thanks guys. That's even better since it will be a 95% street car. And I should have enought ptc clearance with a torquer v3 cam (231/234 .643/.598) right? Im going to check, I know thats the only way to know for sure, but I'm just asking.
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02-11-2013, 10:04 AM
#8
I'm doing this same setup but with AI ported 243 heads. They will be milled to 62cc but that is besides the point. I am mainly going with .040 head gaskets for better quench but it seems guys on here rarely bring this benefit up. Anyone ever have problems with too little quench when running a .040 gasket?
AI says it will work fine but they prefer OEM gaskets for longevity?? they say the more you deviate from OEM, the higher probability of long term issues. Has anyone ever had long term issue when using .040 gaskets on a H/C car?
AI says it will work fine but they prefer OEM gaskets for longevity?? they say the more you deviate from OEM, the higher probability of long term issues. Has anyone ever had long term issue when using .040 gaskets on a H/C car?
02-11-2013, 12:37 PM
#9
Cometics are more prone to leaking if you don't prep the engine well ahead of time. They require a cleaner surface than the GM MLS gaskets. I'm going with them because I have an 02 with MLS gaskets already, so it should be easier to clean vs those horrible graphite gaskets that fall apart.
Since GM uses MLS as well, I don't think there is any long-term disadvantage for Cometic MLS vs the GM MLS.
Since GM uses MLS as well, I don't think there is any long-term disadvantage for Cometic MLS vs the GM MLS.
02-11-2013, 10:46 PM
#10
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I'm doing this same setup but with AI ported 243 heads. They will be milled to 62cc but that is besides the point. I am mainly going with .040 head gaskets for better quench but it seems guys on here rarely bring this benefit up. Anyone ever have problems with too little quench when running a .040 gasket?
AI says it will work fine but they prefer OEM gaskets for longevity?? they say the more you deviate from OEM, the higher probability of long term issues. Has anyone ever had long term issue when using .040 gaskets on a H/C car?
AI says it will work fine but they prefer OEM gaskets for longevity?? they say the more you deviate from OEM, the higher probability of long term issues. Has anyone ever had long term issue when using .040 gaskets on a H/C car?
I haven't heard anybody having many issues with the cometic gaskets running N/A. I'd hope not at 90 bucks a piece lol
02-11-2013, 11:02 PM
#11
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I just finished my top end Stage 2.5 LS6's TSP's 64cc w/ the Cometic .040 gasket set for the added qunech, and I'm glad I did. No knock w/ 28* of timing spinning it to 6800. I believe my CR is 10.95:1 as was brought up earlier in this thread, so if you are running 62cc chambers, you should be <11:1. Qunech is a great thing, adds compression, and helps against detonation. Oh, and I picked up my set for $150 through Texas Speed.
02-12-2013, 11:03 AM
#12
I just finished my top end Stage 2.5 LS6's TSP's 64cc w/ the Cometic .040 gasket set for the added qunech, and I'm glad I did. No knock w/ 28* of timing spinning it to 6800. I believe my CR is 10.95:1 as was brought up earlier in this thread, so if you are running 62cc chambers, you should be <11:1. Qunech is a great thing, adds compression, and helps against detonation. Oh, and I picked up my set for $150 through Texas Speed.
Glad to see others realize the benefit of closer quench as well.
05-25-2016, 08:44 PM
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Help!!!!!! 
07-08-2016, 10:25 PM
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I've reading for about 3 weeks now and I can't really find the answer that I'm looking for. I have a 5.3 04. I'm wanting to get a set of 243 or 799 to put on it. But I'm gonna run a turbo to. If the 243 drop the compression what do I need to do to bring it up to factory or a little higher. I have the ls6 intake also I'm wanting to run a magic stick 3 cam until late the turbo is done. Beehive valve Springs, pretty much every thing ls6 on top of a 5.3. Can one of u guys clear this up for me. Can I run the 07 up flat top 5.3 pistons and rods in my p4 5.3 also
07-11-2016, 07:47 AM
#17
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Quench distance really starts to shine when you start to talk about flame propagation. The tighter you can keep the piston to the head, the more turbulant the mixture in the cylinder becomes, the flame spreads better, and lights off quicker. This allows you do decrease ignition timing and still maintainin burn characteristics.
With a tight quench, you no longer need say 38 degrees of ignition timing to get things started in time to have the flame spread and create max cylinder pressure when desired. The tight quench allows the flame to start and spread fast enough to only need maybe 30 degrees. This reduces negative torque. What is negative torque you say? For those 38 degrees of ignition timing before TDC, the cylinder pressure is rising, and trying to force the piston down, even though it still has to be coming up. This wastes alot of energy and thus kills a certain amount of power. Usually it is offset by making more cylinder pressure at optimal time which increases total output. BUT, if you can make that cylinder pressure at the same time (not lose any peak pressure), and still reduce negative torque by 8 degrees, you're winning on all fronts.
Optimal quench is 0.000 when hot. You literally want the piston to just give an angel kiss to the head. So, considering rod stretch with both temperature and rpm, and thermal expansion of all other components as well, that optimal cold quench number typically comes to around .035-.040. Engines that spin higher rpm need a larger value because the rods will stretch more at high rpm. Engines with aluminum rods will also need considerably more quench.
For most applications we're going to talk about here, I'd shoot for about .035 (or tighter if you're feeling ballsy) quench. Since most LS1's are calculated with the piston .005-.008 out of the hole, this makes a .040 gasket ideal. Take your .040-.005=.035 Using a different combustion chamber is a much better way to reach desired compression than changing head gasket thickness. In your case, you get desired compression and at the same time are bettering your quench by using a .040 gasket, nice work!
With a tight quench, you no longer need say 38 degrees of ignition timing to get things started in time to have the flame spread and create max cylinder pressure when desired. The tight quench allows the flame to start and spread fast enough to only need maybe 30 degrees. This reduces negative torque. What is negative torque you say? For those 38 degrees of ignition timing before TDC, the cylinder pressure is rising, and trying to force the piston down, even though it still has to be coming up. This wastes alot of energy and thus kills a certain amount of power. Usually it is offset by making more cylinder pressure at optimal time which increases total output. BUT, if you can make that cylinder pressure at the same time (not lose any peak pressure), and still reduce negative torque by 8 degrees, you're winning on all fronts.
Optimal quench is 0.000 when hot. You literally want the piston to just give an angel kiss to the head. So, considering rod stretch with both temperature and rpm, and thermal expansion of all other components as well, that optimal cold quench number typically comes to around .035-.040. Engines that spin higher rpm need a larger value because the rods will stretch more at high rpm. Engines with aluminum rods will also need considerably more quench.
For most applications we're going to talk about here, I'd shoot for about .035 (or tighter if you're feeling ballsy) quench. Since most LS1's are calculated with the piston .005-.008 out of the hole, this makes a .040 gasket ideal. Take your .040-.005=.035 Using a different combustion chamber is a much better way to reach desired compression than changing head gasket thickness. In your case, you get desired compression and at the same time are bettering your quench by using a .040 gasket, nice work!
04-04-2017, 01:53 AM
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I just finished my top end Stage 2.5 LS6's TSP's 64cc w/ the Cometic .040 gasket set for the added qunech, and I'm glad I did. No knock w/ 28* of timing spinning it to 6800. I believe my CR is 10.95:1 as was brought up earlier in this thread, so if you are running 62cc chambers, you should be <11:1. Qunech is a great thing, adds compression, and helps against detonation. Oh, and I picked up my set for $150 through Texas Speed.
what cam are you running with this setup?
