I have a 99 312 fastech with 454 mags. I recently took the water box off for repairs and inspected the exhaust and found that the starboard engines inner liner of the stock exhaust pipes were melted and colapsed inside. The port side is fine.

Does anyone know why this would happen, neither engine has ever gotten hot.

Thanks Guys

check for a blockage where the water exits the manifolds into the exhaust tubes.

Thanks I'll try that. I have some new pipe that should be here today and I will inspect everything before I put the new ones on. That would make sense because one pipe is worse than the other on the same motor.

I put the new pipes on today and inspected the manifolds, ran it on the muffs in the drive and everything appears to be OK. I will check them more often to make sure there OK. Let me know if anyone else has any idea's. thanks