Riderfan - If you already had the manifolds, I would go the complete route that Formulajones suggests, but be aware that the Pypes mandrel system will need customization to fit properly. In another thread on this site, CCass from PY is having a new better bent 2 1/2" mandrel system bent and stocked that will require a lot less messing with and fit much better that the current system. It will cost more he said since they will require more work before they go out the door. I have a fairly stock '70 YH 455 (small valve Bonneville motor) with the stock A-body logs with 2 1/2" mandrel bent headpipes from PY back older 2 1/4" turbo mufflers and tailpipes that does a good job (in a '70 Lemans). We did opened up the exhaust outlet in the manifolds by grinding them to 2 1/8" to 2 1/4" since they were off the engine. That was as big as we could make them without before getting too thin for a good seal. The existing outlets were 2 1/16" (+), so we didn't accomplish much. The motor on the dyno with those log manifolds and the headpipes we used on the car made 390 hp/ 510 tq. easily with a mild cam (Summit 2802) and 9.9:1 compression.
Dennis
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