75 450Sl. I want to replace the exhaust manifolds to eliminate the "vapor lock" issue. It starts hard after heating up and after it chuks and spits it will run fine again until next restart when hot. I live in AZ and it is still 95 degrees this time of the year. I read about the changing of the manifolds to 77 or 78 to keep emissions but move the cat under the car to rid the engine compartment of some heat. Jay Gibbs went to the 74 so I was wondering all he removed and what kind of tuning was required.