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I can make my own header. But what size tubing can i go with, and is there any need for back pressure like on piston engines????this is for a 1980 12A THAT WILL BE EITHER STREET OR BRIDGE PORTED(OR CUSTOM PORTED (EXPIREMENTAL :D) I am new to rotary modding :D !!!! Thanks , Andrew

Backpressure is a myth... NO engines need backpressure. What all engines need (or rather, prefer) is tuned resonance.

I recommend getting the Racing Beat catalog, because it is also a pretty good base of technical info. Also good is Paul Yaw's technical articles, can be found on his site personal.riverusers.com/~yawpower

Most people recommend 2" tubes with about 110 inches before they collect... this is extremely long! The main problem is clearance under the chassis.