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Thread: Cometic head gasket better than Mopar?

  1. #1
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    Cometic head gasket better than Mopar?

    I ran my car out in high gear this evening at high boost. It was 28 to 30psi+. Not sure exactly, because it was HAULING A$$ and I was afraid to look at the guage. But anyway, the headgasket got pushed out, I know at least in cylinder #4 because I can see it sticking out from under the head. The plugs look fine other than #4 being wet, with no signs of detonation on them. No oil blew out anywhere, and the dip stick was still in place. I was able to limp it the 1/8th mile or so back to the house. Is a Cometic gasket going to be better for high boost and high cylinder pressures? What are some of the reasons other than just shear pressure to cause a head gasket to completely blow out, (timing,detonation,head lifting, needs coolant mod to #4 etc.?). If I can get a few more bugs worked out this thing is gonna fly. I nailed the throttle from around 50mph in 3rd gear (high), and in less than an 1/8th mile on my test strip I was doing well over 100mph! I know one thing, when I pull the head, the waste gate will become external. The internal gate is useless. I had straight manifold pressure going to the wastegate no bleeds or anything, and it still will boost that high!

  2. #2
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Cometic head gasket better than Mopar?

    Cometic way better than MP

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  3. #3
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    Re: Cometic head gasket better than Mopar?

    Thanks for the reply! I'm having growing pains, and I guess I found a weak link. I just hope it didn't kill my head!

  4. #4
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Cometic head gasket better than Mopar?

    If it blew out the corner, make sure it was not over torqued, that will do a MP gasket in too.

    Hopefully it was from pressure (blown) not heat (burned) too!

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  5. #5
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    Re: Cometic head gasket better than Mopar?

    This is the first Mopar head gasket I have blown in many years. I've been wondering when it might blow. I'm finally getting cylinder pressures up there to do some serious damage. Either in making good power or in trearing up crap!!

  6. #6
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    Re: Cometic head gasket better than Mopar?

    I've yet to tear it down, but by the looks of the plugs,(with several 28psi+ blasts on them) I think (hope) it was just from pressure. I was shooting 105lbs per hr of alky in it at that boost level to help keeps things cool and control detonation. But I did have only 93 octane in the fuel tank. The head was torqued with new bolts to 85ft lbs.

  7. #7
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    Re: Cometic head gasket better than Mopar?

    Only 85 ft-lb with bolts? The 45-65-65+1/4 turn usually nets ~95-100 ft-lb for me. Maybe under-torqued for the higher pressure?

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    Re: Cometic head gasket better than Mopar?

    Quote Originally Posted by BadAssPerformance View Post
    Only 85 ft-lb with bolts? The 45-65-65+1/4 turn usually nets ~95-100 ft-lb for me. Maybe under-torqued for the higher pressure?
    That may be the case. I just didn't was to squish it out. I've been torquing them that way for years. I guess with the Cometic gasket I'll torque them to 95 ft lbs or so.

  9. #9
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    Re: Cometic head gasket better than Mopar?

    Quote Originally Posted by glhs875 View Post
    That may be the case. I just didn't was to squish it out. I've been torquing them that way for years. I guess with the Cometic gasket I'll torque them to 95 ft lbs or so.
    I don't think I went that high, but I was using ARP studs too...

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  10. #10

    Re: Cometic head gasket better than Mopar?

    Didn't Zelowski say 85ft/lbs for all but 90 on the corners? (dodgegarage site)

  11. #11
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    Re: Cometic head gasket better than Mopar?

    Just checked, that was re-torquing, not initial torque.

    I would only undertorque the corners if for sure you know that the gasket is getting squished out because of overtorquing them.

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  12. #12

    Re: Cometic head gasket better than Mopar?

    I know I obliterated an MP gasket, as in an entire inch of the back #4 corner was ripped apart and the fire ring was protruding straight out of the end of the head. That was at 24 psi on ARP studs at 90 ft/lbs. That was also the pull after the 407 whp pull. I think some detonation caused the horrific blowout.

    Regardless, I don't really put any motors together, TD or not, without a Cometic in them. I just see them as far superior to hold the motor together at high cylinder pressures.

    Now- I know some people like them as a "fuse," but if everything is done right there shouldn't be a need for such a fuse. Have a wideband in the car at all times, monitor knock and rip the hell outta' her!

    About the wastegate issue- if you had straight manifold pressure to it, the line must have either come off, or the puck/arm assembly is hanging up on something. I'm having a hard time seeing the size of the wastegate hole being an issue........ the more deciding factor is did it creep to that boost, or initially hit that boost?

    Regardless, externals kick arse for sure! Especially when you vent them to atmosphere with a separate dump tube

  13. #13
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    Re: Cometic head gasket better than Mopar?

    I'm pretty much a newbie with these engines but I put a Cometic with studs in mine. No problems so far, (at least with THAT part) but then not much experience either.

    When you look at the two gaskets, side by side - no question.
    Then consider that both the studs and the Cometic are reusable - no question - ditto.

    ARP Studs + Cometic =
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    Re: Cometic head gasket better than Mopar?

    They claim it but I do not see how a Cometic is re-useable when the little ridges get crushed when it is torqued down.

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  15. #15
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    Re: Cometic head gasket better than Mopar?

    Quote Originally Posted by BadAssPerformance View Post
    They claim it but I do not see how a Cometic is re-useable when the little ridges get crushed when it is torqued down.
    Well, ya got me there. Haven't had cause to re-use it . . . yet.
    John Laing

    "The sole condition which is required in order to succeed in centralizing the supreme power in a democratic community, is to love equality, or to get men to believe you love it. Thus the science of despotism, which was once so complex is simplified, and reduced . . . . to a single principle."
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    -- Justice Antonin Scalia

  16. #16
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    Re: Cometic head gasket better than Mopar?

    About the wastegate issue- if you had straight manifold pressure to it, the line must have either come off, or the puck/arm assembly is hanging up on something. I'm having a hard time seeing the size of the wastegate hole being an issue........ the more deciding factor is did it creep to that boost, or initially hit that boost?

    I've had a problem with the inertal gate from the first time I've ran this combo. I can set the base to where I want it, and it hits that pretty quick and holds. But then starting at around 5000 to 5500 rpm, the boost climbs, creeping quickly to probably a little over 30psi by 6200 to 6500rpm in second and third gears. It will only climb to around 18 to 20 psi first gear. And that's with a 12psi base (plumbing straight to mani) wastegate setting. It's uncontrollable in the upper revs unless I use a bov or something to limit max boost. I think the bov has become stuck or something hear lately because my boost has been creeping again like before. The turbo is working more like a supercharger with the way things are. Now I'm sure I could tighten up the waste gate can to give more intial boost. I've tried 3 diifferent wastegate cans checking all of them with compressed air at low pressure for operation. The original one that came with the turbo gave no less than 15psi. I put a weaker can on to give a min of 10 to 12psi. I've about decided to use both an internal and external wastegate. Use the internal to control the ramp up of the boost for street tire traction, and then use the external to limit max boost. I think that could work real well.

  17. #17
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    Re: Cometic head gasket better than Mopar?

    [QUOTE=8valves;114161]I know I obliterated an MP gasket, as in an entire inch of the back #4 corner was ripped apart and the fire ring was protruding straight out of the end of the head. That was at 24 psi on ARP studs at 90 ft/lbs. That was also the pull after the 407 whp pull. I think some detonation caused the horrific blowout

    Now- I know some people like them as a "fuse," but if everything is done right there shouldn't be a need for such a fuse. Have a wideband in the car at all times, monitor knock and rip the hell outta' her!





    Mine blew out pretty much the same and on the same cylinder. I'm gonna do the #4 coolant mod, and most likely pull a few deg of timing above 26psi. And use a Cometic gasket.

  18. #18
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    Re: Cometic head gasket better than Mopar?

    I just cleaned mine up and used copper spry on it when I reused mine. It held all season and some 27 psi pulls towards the end.
    SDAC member "It's not the ride, it's the rider."

  19. #19
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    Re: Cometic head gasket better than Mopar?

    any detonation at those pressure levels will lift the head and blow gaskets if not warp stuff...i know from experience...

    another thing, 1* of timing will often do the trick when tuning...an 1* can cost you a lot of power if you go too far...i say get this: http://cgi.ebay.com/ebaymotors/NEW-K...spagenameZWD1V

    I've got one of these in my car and its very useful in fine tuning timing, it's also rather cheap considering that most units require use of the gm ESC, which are getting annoying to get ahold of.

  20. #20
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    Re: Cometic head gasket better than Mopar?

    I like it.

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