Reply to "180s on the street – does it make sense?"

Though the 360 degree 8 into 1 is definitely unique, it may be a bit too unique for me. I’m actually going to build a second set for my GT40 replica as it will also eventually have a similar engine and will be 9.5” deck with C302B port position. The 40 definitely needs to be 180s and with the recommendation from Burns Stainless for my build, it’s going to take some doing. Burns recommended two steps from an initial diameter of 1 ¾” to 1 7/8" to 2” at the collector with a 2 3/8” merge back up to 3” cone and then straight through 3” by 17” (or so) long mufflers. The optimum total primary length for my combo was 36” but I don’t think it can be done in less than 38”. When Mike Trusty did his GT40 (which has a stouter cam than what I have planned) his optimum length was only 29-30”. However he found about 38” total primary was about the minimum possible.

The BF301s and C302Bs heads I have on hand have about 1 5/8” exhaust ports. Though starting with 1 ¾” will be nice for header bolt clearance, stepping twice to 2” is going to take some careful planning through all the twists and turns. Below is a picture of Mike Trusty’s GT40 installation. He did this in one step for the primaries. –Very nicely done I might add. I’m going to have to study the matter to determine if I can make the steps occur in practical locations. It’s bound to result in a more expensive pile scrap stainless mandrel bent tubing. I understand harmonics and how the primary length relates to scavenging but even after speaking to Vince Roman at Burns, I’m not sure I fully appreciate the benefits of (multiple) steps. Vince indicated the ideal header continually increases in cross sectional area but I could not get a sense of the performance trades versus no step at all. I need to consider whether it’s even worth the trouble. -Doubtful for a street car. It definitely complicates planning and fabrication.



Best,
Kelly