Cometic Vs. Gm
04-26-2007, 05:30 PM
#1
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Cometic Vs. Gm I know this has been beat to death, but here why I ask. Why my heads and pistons the gm MLS puts me right at 11:1, the cometic .040 puts me at 11.25:1. The idea of this setup is for the most mid range pop which is why I would rather have the compression up above 11:1. My main concern is this, during the summer when the IAT is up there and engine temp is as well. Would the tighter quench and slightly higher compression aid in fighting off knock, or make it worse? Oh yeah, 346 stock type shortblock.
04-26-2007, 07:01 PM
#3
The added knock resistance you get from the tighter quench will offset the tendancy to detonate with the higher static compression. Basically, you will be no worse off with the thinner gasket, but you gain the torque benefit that comes from the 3 tenths of a point you'll pick up in compression. Basically, there are few downsides to going tighter in quench. Tighter P to V clearance and higher cost are the only ones I can think of. For most people, it makes good financial sense. 
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
04-26-2007, 08:07 PM
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Originally Posted by Patrick G
The added knock resistance you get from the tighter quench will offset the tendancy to detonate with the higher static compression. Basically, you will be no worse off with the thinner gasket, but you gain the torque benefit that comes from the 3 tenths of a point you'll pick up in compression. Basically, there are few downsides to going tighter in quench. Tighter P to V clearance and higher cost are the only ones I can think of. For most people, it makes good financial sense.
Brandon
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04-26-2007, 09:50 PM
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I was going to use .040 Cometics. Then I was told, by a very reputable vendor, that the .034 quench is a little too tight for a stock short block. Especially if it's a street car. So... I ordered .045 Cometics
04-26-2007, 09:53 PM
#9
Originally Posted by xfactor_pitbulls
Have some QTPs coming, been waiting a while to get a set of those.
Brandon
Brandon
And to those who asked, you can pick up a minimum of 5rwhp/5rwtq with the 3 tenths increase in compression. With a big snotty cam (the kind that gives you low dynamic compression), the difference can be close to 10 rwhp.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
04-27-2007, 08:15 AM
#11
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I think you can get that compressed thickness with the SES Titans, but they aent any cheaper. Fel-Pro advertises a thin gasket, but as I understand, it is actually closer to .050 than .040.
04-27-2007, 08:59 AM
#12
The 1041 Fel Pro gasket is .041", but it's designed for 4.0" bores. Ever since the LS2 came out, the cost jumped up a bunch (Corvette Tax).
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
02-29-2008, 09:08 AM
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What's the latest on the cometic sealing issues that some people are having? What tricks/techniques can be used to ensure proper sealing?
02-29-2008, 10:51 AM
#16
Clean and flat are the key words. I picked up a machinist straight edge to check my block. I already checked my new AFR heads and they are darn near perfect for flatness.
Also, if you search, Tony Mamo has a method of block preparation to ensure that the block is clean with no high points.
Also, if you search, Tony Mamo has a method of block preparation to ensure that the block is clean with no high points.
02-29-2008, 01:47 PM
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Clean and flat are the key words. I picked up a machinist straight edge to check my block. I already checked my new AFR heads and they are darn near perfect for flatness.
Also, if you search, Tony Mamo has a method of block preparation to ensure that the block is clean with no high points.
Also, if you search, Tony Mamo has a method of block preparation to ensure that the block is clean with no high points.
02-29-2008, 03:29 PM
#18
Originally Posted by Tony Mamo @ AFR
NO copper spray. The manufacturer of the gasket calls for a dry install....I would imagine they know what they are doing.
I have built a handful of LS1's with Cometics and never experienced a problem with leaks. It comes down to the proper prep and two very flat surfaces. Assuming the block is straight and the heads are also (which can be checked with a machinist's straight edge if in doubt) what I have done successfully in the past is to use a medium length bodyman's longboard with either 320 or 400 grit wet/dry sandpaper and I use WD40 as a lubricant. This is of course after removing the larger debris that might be left over from the removal of a composite style OEM gasket. The later model OEM stuff uses an MLS type which usually comes off without much drama or left over residue on the block surface. Anyway....work the longboard diagnally over the blocks deck (remove the dowels) and go in different directions diagnally right, diagonally left, and even straight across. Be generous with the WD40 and the paper will cut a little better and last longer. Wipe clean when your done and you should have a very clean shiny deck with no dull areas which would indicate a low spot. This process also removes some of the risers in the metal from the milling of the deck and leaves a nice smooth surface for the Cometic gasket to seal to. MLS style gaskets need a fairly smooth finish to seal up correctly. I usually do the exact same prepwork to the deck of my cylinder heads, even though the mill we use at AFR leaves them very smooth....I just spend less time on the heads because they are real staight and very smooth right out of the box...
Hope this info helps...
Tony
I have built a handful of LS1's with Cometics and never experienced a problem with leaks. It comes down to the proper prep and two very flat surfaces. Assuming the block is straight and the heads are also (which can be checked with a machinist's straight edge if in doubt) what I have done successfully in the past is to use a medium length bodyman's longboard with either 320 or 400 grit wet/dry sandpaper and I use WD40 as a lubricant. This is of course after removing the larger debris that might be left over from the removal of a composite style OEM gasket. The later model OEM stuff uses an MLS type which usually comes off without much drama or left over residue on the block surface. Anyway....work the longboard diagnally over the blocks deck (remove the dowels) and go in different directions diagnally right, diagonally left, and even straight across. Be generous with the WD40 and the paper will cut a little better and last longer. Wipe clean when your done and you should have a very clean shiny deck with no dull areas which would indicate a low spot. This process also removes some of the risers in the metal from the milling of the deck and leaves a nice smooth surface for the Cometic gasket to seal to. MLS style gaskets need a fairly smooth finish to seal up correctly. I usually do the exact same prepwork to the deck of my cylinder heads, even though the mill we use at AFR leaves them very smooth....I just spend less time on the heads because they are real staight and very smooth right out of the box...
Hope this info helps...
Tony
