ok heres what im doing i got a 13b from an 85 SE and i have installed it in the back of a 1970 vw bug . so i got to build a custom exhaust for it since the stock manifold hits the trans cradle. im planning on using this flange http://mazdatrix.com/getprice.asp?partnum=16187. then build a 2 into 1 collector install my wide band there. then into a pre silencer then a U bend into a muffler. my question is there a certain distance the presilencer needs to be from the exhaust ports? will this just be god awful loud? i plan on using a sport bike muffler i have here. will this be sufficient back pressure for the engine? what size diameter pipe should i use? ID? OD? i plan on using stainless. if its a factor i plan on using the stock FI with a megasquirt.

thanks in advance
andrew

 

Hey Bug, sounds like a cool project. I recently built a custom exhaust maniflod for my Bugeye that I jammed a 13B into. I used two 2 inch pipes for the manifold then went to 2 1/2 after the collector. My engine uses side draft carbs so back pressure is not an issue. As for pre-silences I'm using two and they are install just after the collector. Also I plan on wrapping the header with ceramic tape to help control heat and noise. Hope this helps good luck. Dave