I have a 351w that has a header leak all the way across. As you can tell by the gasket it is leaking out the bottom on every cylinder. Is this the header bolts backing out or are the side pipes twisting the headers with the engine torque?
I bought some spilt locking washes to see it I can stop the bolts backing out. If that fail I will drill the head of the bolts for saftey wiring. I had to retorque them a few times over a few short hours of running.
