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Premium Member
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No, you don't need D port headers. Just make sure the holes in the header flange are bigger than in the head all the way around.

Most race headers for D ports are purposely done this way.
Once I read that low speed reversion is along the low side of the pipe, while
high speed outflow is along the top side. They make the bottomside flat to allow multiple exit paths for intial cylinder blow down with out slowing charge speed.
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