Quote:
Originally Posted by jocko
On another note, 3" seems way too big in my mind for a 230 six. 2.25, 2.5 max I would think. But let others chime in on that one.
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The bigger the exhaust, the lower the torque. Unless you have done work on the head and cam, I wouldn't go over 2.5. My 235 (earlier series engine) has 2" exhaust with a 3/4 race cam and has turned just short of 5,000 rpm. The newer 230 head flows better.
Air flow is relative to area. 2.0" diameter has 3.1 sq in. 2.25" has 4.0 sq in, 2.5" has 4.9 sq in, 3" has 7.1 sq in area. The 2.5" gives over 1.5 times the air flow, which is huge, with a corresponding loss in low end torque, which is what is needed to move a heavy pickup.