As I have posted here in i-Club. I recently purchased a header from SSAutoChrome. Worst piece of junk ever, it did not mate properly with the exhaust manifold, and the gasket completely got toasted. Here is my concer, I know the block is made of aluminum, but how much heat can it take before deforming? And is it possible for the exhaust to gain more heat when mix with the Oxygen rich outside air and damage the block? I am very concerned because I will not getting a replace header for another few days, and I hope that the damage is not already done.

It isn't necessarily the overall temperature that will damage anything, but the change in temp over a certain period of time. To give you an example, lets say you have a car that has aluminum heads and an iron block. You go out and race around and run the engine really hot from high rpm driving. You then stop the car after you are racing around and it happens to be cold out. You have a high temperature condition going on that will cool down quickly due to ambiant air temps. Plus, since the heads and block are of a different metal type, they will contract from their heated expanded state at a different rate. This 'can' cause damage if you do this a lot. However, with Subarus, you shouldn't have this problem. They are made to run at higher temperatures due to having a turbo. I wouldn't worry about anything with your car. It would most likely only cause damage if you had a huge leak right where the exhaust manifold connects to the heads. Even then, you shouldn't have a problem. I'm horrible at explaining things and I just gave a short explanation and not a long one to bore you.

Looks like your right guys. I just did some rework on the header, the only thing I saw carbon deposits around the manifold. Thank God, the mind can do wierd things when your worrieing.

Haven77