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Stainless O-ring position on Grommet/Stopper Type MLS Gaskets

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We have an RB26 that we're having trouble with head sealing. We first lifted the head with a standard Cometic MLS gasket and ARP 2000s. About 28lbs and 22deg of timing at 9300 (140mph through traps). C16 race fuel so not knock limited. The block and head were both machined prior to install. We resurfaced the head and switched to a Nitto stopper type gasket, new ARP 2000 studs, and added a coolant pressure sensor. This worked great for quite a while and we were able to up boost to 39lbs as well as gain 13mph through the traps (153mph). Clearly making much more power. Then going through the traps last weekend the head lifted again. Coolant pressure showed constant pressure until a second before lifting off the throttle it quickly spiked up 17lbs and remained there down the return road.

I saw Andre post the below in response to someone else's similar issue. Andre has also mentioned this in a head sealing webinar.

"Hey Roni, thanks for sharing your experiences. I've replaced more head gaskets than I care to remember on our drag engines and I've tried just about everything to seal these engines. the solution we ran in our own drag car was an HKS stopper type MLS gasket that was 1.2 mm thick coupled with a stainless o-ring in the block with a protrusion of 0.005-0.006" and a set of 12 mm L 19 studs. This was a solid solution that worked well until we got into the mid 50 psi vicinity. We tried a copper gasket with o-ring and a receiver groove and couldn't hold 40 psi :("

Where would one locate this ring on the gasket? On the inside edge of the stopper? On the backside of the stopper? Behind it? Any assistance would be great! I suspect this is my next course of action. If I were to o-ring with a standard MLS gasket I would assume the o-ring would sit on the top of the gasket embossment. Please correct me if I'm wrong.

Hello i have only run them on the outside of the stopper gasket oring on the two I have done, they worked fine at the 56 psi I was running It would be upgrading the hed stud to L19 tho that will be the first thing that will stretch

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