Are Cometics worth it?
09-20-2005, 01:35 AM
#1
Are Cometics worth it? I have a 2002 Z28 with a G5X3 cam, and Im putting on my AFR 205's here soon. Im going to have them milled to 59cc's. I was wondering if I should go with the stock size gaskets, or go with the Cometic's in the .040/.043 range. I heard that the head surface has to be perfect to ensure a good seal. Ive also heard that the GM's are more forgiving in that area. This car is a daily driver, and I really cant afford to have the car down due to leaking head gasket problems. Ive been told two different things, by two different reputable builders on this site.
Would I see much more power if I went with the Cometics, over the stockers? Im not worried about the cost. Im more worried about the reliability. I think it would be safer/more reliable to go with the stock size gaskets, but Im wondering if it would adversely affect the car. Im not too familiar with quench, so any insight you guys have would be great.
Basically, to sum things up, I would have more piece of mind going with the GM gasket, if I knew it wouldnt rob a ton of power vs. the Cometics. Once again, Im more concerned with reliability, more than performance, as long as it isnt a HUGE difference. What are your opinions? Thanks in advance, guys!
Would I see much more power if I went with the Cometics, over the stockers? Im not worried about the cost. Im more worried about the reliability. I think it would be safer/more reliable to go with the stock size gaskets, but Im wondering if it would adversely affect the car. Im not too familiar with quench, so any insight you guys have would be great.
Basically, to sum things up, I would have more piece of mind going with the GM gasket, if I knew it wouldnt rob a ton of power vs. the Cometics. Once again, Im more concerned with reliability, more than performance, as long as it isnt a HUGE difference. What are your opinions? Thanks in advance, guys!
09-20-2005, 07:25 AM
#3
TECH Senior Member
Originally Posted by Z06-Dave
If you like to spendind triple the money, and like chasing down leaks the Cometics are the ones you want.... 
I've used Cometics on scratch free deck surface with no problem for over 3 years. Prepping the areas needs more care but is not ****.
The benefits of it is with higher compression and todays low grade gasoline, you need to do anything possible to minimize chances of detonation.
Tight quench is one way to do that.
Other benefit of tight quench is more power. How much is relative to your combo, but i've experienced anywhere from 5>12rwhp difference.
Also thinner gasket is a way to increase compression without milling more. Milling too much will result in less head flow which eats up a few ponies that we so desperately seek.
That is the difference between slapping combos together and maximizing combos. Every little bit helps and end results have shown the difference between a H/C combo without attention to detail and a maximized one that makes 20>30rwhp more. (optimizing includes quench, tune, degreeing cams, playing with the advance retard etc....)
Also Cometics are reusable so if for whatever reason you have to yank the heads off, no messy and time consuming deck cleaning needed.
Last edited by PREDATOR-Z; 09-20-2005 at 07:32 AM. Reason: Adding more info
09-20-2005, 08:20 AM
#5
I have done two installs using them, with no issues at all. I did use copper spray sealant on both.
The only advice I am going to give on this is a H/C setup is about the details. That means every bolt-on in the book, tight quench, high compression, head flows numbers that match your cam choice, correct pre-load.... ALL the small details!!! If you can handle not making that last few HP don't worry about any of this. If you are trying to get it "all" you are going to have to do it "all"...
Good Luck,
The only advice I am going to give on this is a H/C setup is about the details. That means every bolt-on in the book, tight quench, high compression, head flows numbers that match your cam choice, correct pre-load.... ALL the small details!!! If you can handle not making that last few HP don't worry about any of this. If you are trying to get it "all" you are going to have to do it "all"...
Good Luck,
09-20-2005, 08:22 AM
#6
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Originally Posted by PREDATOR-Z
This is not what I would consider a professional comment.
It is my personal experience. After installing my cometics, numerous vendors have told me they do not even recommend them.
They certaintly are better for your reasons stated, but for the average DIY'er not looking for every single last HP out of their combo, the stockers are more than acceptable.
09-20-2005, 08:32 AM
#7
Originally Posted by Z06-Dave
...They certaintly are better for your reasons stated, but for the average DIY'er not looking for every single last HP out of their combo, the stockers are more than acceptable.
How do you like your cam??? Is it an XE-R CompCam??? Trending Topics
09-20-2005, 08:49 AM
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I'm on my 3rd set off Cometics without any problems but next time I have to change head gaskets I'm going to try the SCE Titan self sealing copper head gaskets, they're about $30.00 cheaper than the Cometics also.
09-20-2005, 09:42 AM
#9
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I have AFR 205's mounted on Cometic .040" gaskets. I went with the .040" gaskets for all the reasons Predator outlined. I had my heads milled .010" at first because I was running a 224/228 .581"/.588" 112lsa cam on +2 advance. I later measured my piston out the hole at .004", and my p/v at .097" intake, and .128" exhaust. I prepped the deck by making sure it was as clean as I could get it with a plastic ice scraper. I spent some time on it but I would have done this with any gasket. I also found a spot on my deck on the outside of the coolant hole on the #1 cylinder where the head must have been dropped on it during assembly. It was 4 gouges the shape of the outside of the head about 1" long starting about .030" deep to around .005" deep. I was going to scrap the idea of using the Cometics and put a set of GM graphites on because you could see where coolant had traveled in the gouges out to where the space got too thin. I got some FastSteel and mixed some up and filled the gouges with it and believe it or not it closed up the gouges. I have had my heads on and off once since, because I had them milled another .020" for a total mill of .030" and redegreed my cam. I also flycut my pistons with the modified head on and off about 50 times mounted on the Cometics, not torqued, just snug. I used GM bolts both times. I have had this setup since last October and have put ~3500 miles on it and I run the car hard at least once when I drive it. It's too much fun not to. No problems with the Cometics. I didn't use copper sealant either. I have only read about leaks when ARP's are used and only occaisionally. Apparently the torque sequence needs to be redone a few times for whatever reason. I can say from my experience and using the GM bolts, no issues.
09-20-2005, 11:46 AM
#10
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I think Felpro makes a .050 MLS gasket. Also the quench distance from a .040 cometic and .055 is .032 with a cometic and .047 with a MLS. For what it's worth Ken Duttweiler says the tightest quench he would run is .050, the late great John Lingenfelter and Smokey Yunick recomended .037 to .040-ONLY if you know what you are doing. Also with a .040 Cometic and a the 59cc AFR your compression is up to around 11.8-you will need to flycut your piston .080 for adequate clearance as well. Honestly the choice is yours but I think the MLS gasket is within spec for a good quench distance-BUT-if the cometic leaks then your going to wish you ran the MLS.
09-20-2005, 01:16 PM
#11
TECH Senior Member
Originally Posted by Vortech
I think Felpro makes a .050 MLS gasket. Also the quench distance from a .040 cometic and .055 is .032 with a cometic and .047 with a MLS. For what it's worth Ken Duttweiler says the tightest quench he would run is .050, the late great John Lingenfelter and Smokey Yunick recomended .037 to .040-ONLY if you know what you are doing. Also with a .040 Cometic and a the 59cc AFR your compression is up to around 11.8-you will need to flycut your piston .080 for adequate clearance as well. Honestly the choice is yours but I think the MLS gasket is within spec for a good quench distance-BUT-if the cometic leaks then your going to wish you ran the MLS.
In general .040 and .045 are the most commonly used.
BTW, if (and with if, you can put Hoover dam in a bottle), are worried about running proven parts, then just do not mod at all.
I agree with the .035>.040 quench for street use. I've used .045 Cometics on my 3 occasions.
And I wouldn't use Felpro if you gave then to me for free. (but that is just me)
09-20-2005, 03:43 PM
#13
Compression is nowhere near 11.8:1.
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR, and with the G5X3-114, the DCR is 8.3. As a test, think of the 62cc 5.3L heads, they don't come out to 11.3~11.5 and the difference is only 2cc. I'm sorry but the compression difference between the LS1 and LS6 is only .4 and it's 66cc vs 64cc. Hell, 64cc with a .54 is only 10.5, so why would going to an effective 60cc jump the compression 1.3 points??? It doesn't. Anyway, this is why the AFR205 59cc/G5X3-114 combo makes an insane amount of power, because it is very well matched and the DCR is near optimal. Big cams need compression.
I've read on here plenty of times that the AFRs make more consistent HP, but what I've noticed is people use the right combo of parts with the AFR heads. Buy some budget heads, run them at near stock compression, and slap some GM MLS gaskets on there and then wonder why it's 40-50rwhp lower than the AFR headed car with the same cam. It has less to do with the head and more to do with doing it right.
The AFR heads allow for a tighter quench with its double quench area, so anyone saying .37-.50 is thinking of SBC and not Gen-III LS1.
Buy the Cometics.
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR, and with the G5X3-114, the DCR is 8.3. As a test, think of the 62cc 5.3L heads, they don't come out to 11.3~11.5 and the difference is only 2cc. I'm sorry but the compression difference between the LS1 and LS6 is only .4 and it's 66cc vs 64cc. Hell, 64cc with a .54 is only 10.5, so why would going to an effective 60cc jump the compression 1.3 points??? It doesn't. Anyway, this is why the AFR205 59cc/G5X3-114 combo makes an insane amount of power, because it is very well matched and the DCR is near optimal. Big cams need compression.
I've read on here plenty of times that the AFRs make more consistent HP, but what I've noticed is people use the right combo of parts with the AFR heads. Buy some budget heads, run them at near stock compression, and slap some GM MLS gaskets on there and then wonder why it's 40-50rwhp lower than the AFR headed car with the same cam. It has less to do with the head and more to do with doing it right.
The AFR heads allow for a tighter quench with its double quench area, so anyone saying .37-.50 is thinking of SBC and not Gen-III LS1.
Buy the Cometics.
09-20-2005, 03:47 PM
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Does that 1cc flycut equal to about a .080 cut? I was figuring 11.8 with no valve relief and the piston being out of the hole a minimum of -.008. Which formula are you using? I'm using the DCR calculater that JRP has as a sticky. Even Tony said 59cc with a .40 gasket is 11.8?
09-20-2005, 05:21 PM
#16
Originally Posted by JakeFusion
Compression is nowhere near 11.8:1.
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR
Using the RossPiston calculator and J-Rods VE spreadsheet I get 11.8ish to 1. I bounced these same numbers by Tony before on another project, he came up with the same values, 11.8ish.
Considering
59cc chambers
1cc flycut (approx. for .080 cut)
.040 Cometic gasket
.007 out of the hole (average for LS1s)
How did you get 11.26???
09-20-2005, 08:36 PM
#20
Originally Posted by JakeFusion
Compression is nowhere near 11.8:1.
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR, and with the G5X3-114, the DCR is 8.3. As a test, think of the 62cc 5.3L heads, they don't come out to 11.3~11.5 and the difference is only 2cc. I'm sorry but the compression difference between the LS1 and LS6 is only .4 and it's 66cc vs 64cc. Hell, 64cc with a .54 is only 10.5, so why would going to an effective 60cc jump the compression 1.3 points??? It doesn't. Anyway, this is why the AFR205 59cc/G5X3-114 combo makes an insane amount of power, because it is very well matched and the DCR is near optimal. Big cams need compression.
I've read on here plenty of times that the AFRs make more consistent HP, but what I've noticed is people use the right combo of parts with the AFR heads. Buy some budget heads, run them at near stock compression, and slap some GM MLS gaskets on there and then wonder why it's 40-50rwhp lower than the AFR headed car with the same cam. It has less to do with the head and more to do with doing it right.
The AFR heads allow for a tighter quench with its double quench area, so anyone saying .37-.50 is thinking of SBC and not Gen-III LS1.
Buy the Cometics.
59cc AFRs and .040 cometics with a 1cc flycut in the piston, I come up with 11.26:1 SCR, and with the G5X3-114, the DCR is 8.3. As a test, think of the 62cc 5.3L heads, they don't come out to 11.3~11.5 and the difference is only 2cc. I'm sorry but the compression difference between the LS1 and LS6 is only .4 and it's 66cc vs 64cc. Hell, 64cc with a .54 is only 10.5, so why would going to an effective 60cc jump the compression 1.3 points??? It doesn't. Anyway, this is why the AFR205 59cc/G5X3-114 combo makes an insane amount of power, because it is very well matched and the DCR is near optimal. Big cams need compression.
I've read on here plenty of times that the AFRs make more consistent HP, but what I've noticed is people use the right combo of parts with the AFR heads. Buy some budget heads, run them at near stock compression, and slap some GM MLS gaskets on there and then wonder why it's 40-50rwhp lower than the AFR headed car with the same cam. It has less to do with the head and more to do with doing it right.
The AFR heads allow for a tighter quench with its double quench area, so anyone saying .37-.50 is thinking of SBC and not Gen-III LS1.
Buy the Cometics.
with the info given compression comes out to 11.6824236615186 with DCR comming in at ~8.76400758146286.
of course if you want to do it right you'd measure your own deck height, mic the gasket and measure the bore, and cc the combustion chamber. that way there's no guessing.