How good are Cometic MHGs?

[empera]

how good are cometic MHGs for higher boost/HP 7m's? maybe 600-700rwhp?
Maybe this has been covered before i haven't found anything. I might be asking this the wrong way but any information that might help would be greatly appreciated.

thanks,
-emp.

 

[sneakypete]

im running one right now. have been using it since august with no problems running at around 16psi. i plan on turning up the boost this summer once i put in some bigger injectors and some c16. ive heard with a proper tune, that the cometic can take that much power

 

[empera]

yea i wanna maybe go up to 20-25psi...gonna be using 780cc injectors

 

[hottscennessey]

I've used it on my 7M, and my 2JZGE's. Never had any issues, even with a 36psi boost spike. I also re-used it on a 2JZGE without issues.

 

[IJ.]

Emp: You can blow ANY MHG if you get the tune wrong
(I've blown one of each of the Cometic, TMS (same thing rebadged) and a HKS stopper.

Having said this get it right and any of them will work fine.

Flat and Smooth on both surfaces with a retorque after 5 heat cycles with minimal to no boost works for me.

 

[empera]

Emp: You can blow ANY MHG if you get the tune wrong
(I've blown one of each of the Cometic, TMS (same thing rebadged) and a HKS stopper.

Having said this get it right and any of them will work fine.

Flat and Smooth on both surfaces with a retorque after 5 heat cycles with minimal to no boost works for me.

yea thats wat i'm thinking...everything is getting done correctly...TRYING to take my time.

 

[sneakypete]

are you going to make it to etown this spring?

 

[empera]

are you going to make it to etown this spring?

yea i'll be there, if not the supra then the lexus or will take a ride with someone...

are you coming down to the philly meet this year?

 

[CyFi6]

Which MHG is the most forgiving to imperfect surfaces?

 

[sneakypete]

yea i'll be there, if not the supra then the lexus or will take a ride with someone...

are you coming down to the philly meet this year?

i want to.... when is it?

 

[shaeff]

Which MHG is the most forgiving to imperfect surfaces?

Cometic.

 

[jdub]

^^^ Even then, the Cometic spec is 50RA...still has to be flat and very smooth.

 

[empera]

i'm using a cometic now and its done great...i've seen 18 steady and spiked to 22psi (was a little scared) but she's held, not sure which thickness i will be using... I have a .051" new cometic MHG but i'm not sure if i can use it since the person whom i bought my block doesn't know how much was taken off...which kinda made me upset. i'm waiting on hearing back from a machinist who is measuring it.

 

[suprarich]

^^^ Even then, the Cometic spec is 50RA...still has to be flat and very smooth.

Lets add to this some Jdub, for everyone else. Cometic maynot be more or less forgiving than the hks. All we can say is that cometic specs the gasket for a lesser ra than hks. This does not mean that cometic is more forgiving. All it means is that hks wants you to use a higher ra spec than cometic. They both could very well be exactly the same as far as adapting to your overall finish.

 

[bigaaron]

Lets add to this some Jdub, for everyone else. Cometic maynot be more or less forgiving than the hks. All we can say is that cometic specs the gasket for a lesser ra than hks. This does not mean that cometic is more forgiving. All it means is that hks wants you to use a higher ra spec than cometic. They both could very well be exactly the same as far as adapting to your overall finish.

Exactly, we always used HKS gaskets and never had a blown one when it was surfaced correctly. The Greddy is almost identical to the HKS.

I have heard about just as many blown Cometic gaskets as anything else.

 

[sneakypete]

Exactly, we always used HKS gaskets and never had a blown one when it was surfaced correctly. The Greddy is almost identical to the HKS.

I have heard about just as many blown Cometic gaskets as anything else.

when you say anything else.... do u mean metal type hg?

 

[berniek]

Hey, grumpy old man:

Yeah, I'm one too, 67 at next b'day but a kid at heart.

Saw your posting about retorquing studs with an MHG after 5 heat cycles. I checked mine (2.2 mm Cometic) after about 100 miles on a freshened JDM engine. Started on the exhaust side, and found all up to torque spec. Never even took off the intake cam cover. The head and block were properly finished. After reading your post I'm a little worried that I should go through the exercise again, now with 2K miles on the engine. How much torque reduction did you find? I know it gets down to less than half with composition gaskets, at least in older GM engines.

Tnx. Looking forward to your reply.

BernieK
BernieK@technicaldevelop.com

'91T, non-targa, refreshed JDM, Walbro, Lex, 550cc ND injectors, 57 trim turbo at 17 PSI (at 3000 pipe), '98 wheels and engine mounts (strong!), Lipp, modified stock FPR, Treadstone IC, hardpipes, Cometic, ARP, Random Tech 3" single cat downpipe, HKS LET-16 exhaust, Exedy organic clutch (street use), Raptor BOV (recirculated), deflashed valve bowls, exhaust helicoils, tower strut.

Emp: You can blow ANY MHG if you get the tune wrong
(I've blown one of each of the Cometic, TMS (same thing rebadged) and a HKS stopper.

Having said this get it right and any of them will work fine.

Flat and Smooth on both surfaces with a retorque after 5 heat cycles with minimal to no boost works for me.

 

[IJ.]

Hey fellow Old Guy

I see JDub set you straight in the other thread!

It's really important to do the back crack thing as it releases the Stiction on the fastener and allows for an accurate torque to be set.

 

[bigaaron]

when you say anything else.... do u mean metal type hg?

Yes, if you do the surface prep or head bolt/stud torque wrong, any brand of metal headgasket will leak.

Because a rumor went around the forums that "Cometic headgaskets are more forgiving", people think they can forget surfacing the block and/or head and just throw a Cometic on there and it will be fine, which is obviously not the case.

 

[shaeff]

Yes, if you do the surface prep or head bolt/stud torque wrong, any brand of metal headgasket will leak.

Because a rumor went around the forums that "Cometic headgaskets are more forgiving", people think they can forget surfacing the block and/or head and just throw a Cometic on there and it will be fine, which is obviously not the case.

It's simply a misinterpretation. According to the RA value they provide, it's technically more forgiving. (Doesn't need as smooth of an RA, and still needs to be true) That does NOT mean that you should skip machine work when using it, though.

I'm not telling you, Aaron, I'm just putting the information out there.