I know this has been beat to death but I am having problems getting the passenger side gasket to seal. It blows out after 100-200 miles.

The reason is most likely because the old gasket was stuck on the header and I could not scrape it all off. It is not easy to get razor blades in there with the header in the car. Anyone have ideas to get the old gasket off the header?

 

take the header loose at the y-pipe. That should give u enough room to move the header around. Not sure what type of header ya got, mine got the ball type flange, so no gaskets is needed at the bottom. Use factory gm metal gaskets, they will give u a leak free seal, I promise