Quote: this may not help anyone but let me tell you what happened to me and maybe someone will be able to tell me what happened. I had a moroso crank case / header evacuation setup on my 68 GTX.Car ran mid- high 11's and we went to a track for a muffler race. I had an exhaust system put on the car 2-1/2 " with flowmasters.Man it sounded good and when I made a pass it was a SECOND slower,and it blew the intake valley pan up like some stovetop popcorn,all bulged up and blew out the valve cover gaskets!! Unhooked the exhaust and back to 11.70--
Very simple, your 2 1/2" with Flowmasters had more back pressure than 5"hg, once you got on it it went above 5"hg and the back pressure burnt out the check valves and pressurized the crank case
