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Old 06-25-2008, 04:07 PM   #1
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2004 WRB STi
Full Race TS, BW 8374 EFR

Default Anyone have issues with Cosworth head gaskets?

I just got off the phone with Eric, an engineer at Cosworth. First I asked if their gaskets were made by Cometic. He says they are not and they are made by themselves. As far as the Cosworth head gaskets are concerned, they have never had a reported failure. After reading that some coatings on the steel gaskets can get scuffed off, I asked him specifically if this were to happen and he says that what people with supposed gasket failures don't take into consideration is that it is critical that the mating surfaces be absolutely be flat. He went on to say that don't trust anyone when it comes to double checking clearances and tolerances. If that was the case, he says car manufacturers such as Toyota, Honda, Nissan would not be using the nitrile rubber coatings on their oem gaskets. I asked if it that was used in the factory Subaru gaskets and he said not on the entire surface, just certain areas. He also said that the machine shops must have the proper tooling to achieve this. So I asked what kind of info I would need to double check with the machine shop. He says the RA (roughness average) needs to be 20 - 30 or better and to have them double check for mating surfaces flatness.
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Old 06-25-2008, 05:22 PM   #2
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yep, he is correct and this is old knowledge.

Most aftermarket shops CANNOT get the RA finish smooth enough. then you blow a head gasket.
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Old 06-26-2008, 01:36 PM   #3
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We have never had a reported failure is a big red flag to me....thats total B.S.

You know someone has popped one.
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Old 06-26-2008, 03:29 PM   #4
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And if they haven't, they will. Stuff breaks, especially when pushed to the limit.
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Old 06-28-2008, 07:59 AM   #5
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2001 V7 sti


I bought a set of cometic head gaskets and later bought a set of Cosworths. Side by side the cutting profile is quite different.
The cosworths have the folded middle layer which gives a tighter seal around the bore of each cylinder which is the reason I bought them.
My last set of cometics leaked between the chamber and the water jacket. I wont blame the geaskets for that as I had an ecu problem which led to severe detonation.

Overall I have not been able to fault the Cosworth product (fingers crossed).
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Old 06-28-2008, 03:16 PM   #6
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2001 GC8 [622.4WHP]
SOHC / GT35r 25psi


I have a set of Cosworth Gaskets on my RS-t and have had no issues with them as of yet. They have been going strong for over a year now auto crossing and drag racing like crazy. I am impressed.
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Old 06-28-2008, 03:30 PM   #7
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Originally Posted by modaddict View Post
yep, he is correct and this is old knowledge.

Most aftermarket shops CANNOT get the RA finish smooth enough. then you blow a head gasket.
RA needs to be very smooth and the lower the smoother. Old news indeed and is complete logical sense.

My surfaces get done at a 12 RA and haven't had an issue with cometics, yet (sorry, the engineer always leaves room ). Most also know that-that's pretty smooth.
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