So 2" exhaust merged into 3" back should do the trick?



Any more input on the ID of the intake sleeves for a 13b?

 

For your application 42 or 43mm ID and the same port timing and shape as MFR housings. Twin 2in OD primary pipes (90-100in long) into a 2.5in OD collector then a short 2.5 - 3in megaphone and out through your rear muffler.

 

how important is the megaphone?

 

90-100" before the collector? That seems extremely long for such a high overlap motor. I though somewhere around 12" primaries was ideal?

 

Not sure exactly how important the megaphone is but a lot of top cars use them as did Mazda race teams. From what I gather 2.5 - 3in for street and 2.5 - 4in for race.



90 - 100in primary length works for me. In saying that I have yet to try a short header e.g 12 - 14in.

 

Hrm, thats interesting. I just figured that since most stock port headers run close to a 24" primary runner (RB, paceshitter, SDJ ect), a short runner header on a high rev motor would make more since? I suppose that longer primaries could compensate some low end performance, but Ive never heard of anything in eccess of the norm 24".