Hi

I'm having a header made up for my bridgeport 13b. They are going to make the primaries equal length (or as close as possible) and mandrel bent and im thinking the primaries should be 2" inner diameter collecting into 2.5" collector and then megaphoning up to meet with my 3" exhaust. Does anyone have any suggestions on length of the primaries? I cant afford to go through testing lots of different lengths so I just need a ballpark idea. My current header is crush bent, 2" outer diameter and far from equal length (its a complete piece of crap) so I want to get a new header made up before I've finished breaking in this engine because I plan to get it on the dyno. Also do you think I should just have the primaries collect at 3" or do you think starting from 2.5" and then going up to 3" is better? Any other suggestions would be appreciated. Noise levels are not a problem im going for pure power.

Thanks

 

the megaphone at the collector is proven to make more power, so go with it and here's a link with some good advice on primary lengths. I would try and collect them at 18"
http://www.racingbeat.com/Tech/Tech.Exhaust.2.htm

 

On my Peripheral port 13B, I have had good luck by joining the two pipes together, merge down to a 2-3/8" throat, and then very gradual expand to a 3" exhaust pipe.

I run long primaries, at 89" long from engine to collector throat. I have seen some very stong short primary pipe rotaries; the 16 to 18" length primary can work well too.

 

What is the inside diameter of your long primary pipes?

thanks