2" headers

I recently converted spf2122 from street to R, one problem we ran into was with the exhaust in the car last year. We dyno'd the car on a dynojet and were only getting 470 rwhp. The engine dyno showed 615 crank hp so we knew we were lossing quite a bit of hp. This is a 434 CI all aluminum motor with AFR 225 heads. The factory headers are, I believe, 1.5". After contacting Ron Roberts at Fireflyperformance.com ( he had done the pipes on my cobra ) we decided a much larger header was needed. Over the winter Ron made up a new set of 2" pipes out of SS and had them coated for me. Finally got the car on the dyno and picked up 39 hp (with a very fresh trans). Here is a copy of the dyno run. this was performed on the same dyno as before. Unfortunately the previous run's were deleted off the dyno so I cannot give you a full comparison. From a seat of the pants the car has much more power, with street tires, you can spin them in 1,2 or 3rd just by applying throttle. Car completely hooks up with track rubber on it. This was a great upgrade that really lets the AFR heads breath.



Can I ask a few more details about your engine...carbs, intake, C/R?

If you don't mind, could you PM me with a ballpark figure the the exhaust $$?



Just curious. How close does the high point of the headers come to the underside of the clip? Any issues with heat near the fiberglass?

Howard Jones

Did you use the same mufflers as before on the 1.5" headers?

When I build my GTD I used the standard GTD exaust. I did notice that the standard GTD exaust piped had a very small port shape on the flanges and they covered the bottom of the port by as much as 1/8". I also could see that the collector did not transistion into the muffler but instead simply was welded onto the facew of the muffler.This resulted in a 3 inch collector flowing into a 2 inch muffler inlet pipe at 90 degrees to each other.

First I cut off the flanges and welded on new flange's that matched the exaust ports on my FMS alum heads. Then I cut off the collectors from the GTD muffler snd used them to flow into a very low restriction 3 inch muffler (one per side). Farads same engine with the old style exaust (standard GTD as mine was making something like 250HP at the wheels. Mine made 297. Quite a bit more than 10% at the wheels. We even used my mufflers on his car without the flange upgrade and got something like 30Hp at the wheels.

Headers do make a lot of difference but I think the thing to pay close attention to are the header flanges and any restrictions resulting from transistions.

If you had a bad fitting system before with restrictive mufflers I quite believe that you picked up that much power. Increasing the primary size must have helped but I bet it was mostly the quality worksmanship that made most of the improvement.
yes, collector was re-designed and cleaned up. yes, same mufflers - stock spf units. the collectors mount up right before the mufflers, and needed to be re-fabbed with the 2" pipe, these are a cleaner design than the factory collectors. The factory mufflers are 3". I have not run it with my megaphones ( no baffle whatsoever ) as we believe that no backpressure will actually cause us a loss of power, but they do sound great.
they do come close to the fiberglass at the collectors, I used a heat shield product I found on the forum - technofibra I believe, no problems at this point.