I have a 360 with two 450 Holley's tunnel ram setup and compression of 11.2:1 I first blew the driver side head gasket, replaced it with a different type gasket and as soon as I fired it up to make sure nothing was leaking it blew the passenger side. The gaskets that blew was the Fel Pro 1008 Ihad a set of Mr Gasket that I put one on the driver side but plan on putting Cometic on both sides. Does anyone have any clue what could have caused the problem; they blew almost straight across from each other. The driver side was leaking about at the #5 cylinder and the passenger is around the #4 cylinder. I had tooling at my work check the driver side head on their flat stone with dykem paste and everything was good with it. I had 93 octane in it at the time the heads are ported J heads.