[Half-Inch Stud]

I posted longk ago that the exh pulses will interfere in the "Y" in each head, and real bad if a plate is used to block. When EXH crosses-over they interfere with 1-one other CYL. Fill the "Y" to remove heat and reversion caused by the crossover. Of CYLS 4-3-6-5, fill the "Y" completely for best Header (and Manifold!!!) performance.

Yet a torque tube can also occur, if wanted by filling half the "Y". Reversion remains greatly suppressed too. Fill the branch of the "Y" for 6 & 3 to the EXH bowl window.

Reversion mitigation is important. If you run a RA-IV or bigger cam than factory, then i strongly recommend either crossover fill for best results.

[chiphead]

321 Stainless lasts longer than 304 in this application. The 321 is alloyed with titanium, which reduces carbide precipitation and burn through in continuous high temperature operation above 1400F. I did the block off shims, in addition to a phenolic carb spacer, to reduce E10 fuel boiling at operating temperatures. No negative effects once the engine warms up. I'm on the east coast where it gets hawt in the summer.