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I recently had my SPF on a chassis dyno while tuning in an aftermarket EFI with a small block Chevy. It made 415 h.p. and 438 ft. lbs. to the tires but fell off after 5000 rpm. This car should make 50+ more h.p. than it is. After initially thinking we were running out of air, I started looking at the sidepipes. To support 550+ h.p. you need 2 1/2" i.d. minimum on the mufflers. It's hard to tell for sure but these mufflers are 1 7/8"-2" MAXIMUM i.d. I had a super-charged motor in the car before this one and it laid down after 5500 rpm. I didn't put two-and-two together until now.
Anyone else come across this? We have a custom fab shop here in Sacramento that will have a muffler for these pipes. When I figure out which one to use I'll re-post if there's any interest. The problem is unless you dyno the car you may not be able to tell you're losing the power; these things are fast even with mild engines. I will put the car back on the dyno after the muffler swap and post the "after" numbers for comparison. By the way, the tuner who is helping me found 100 h.p. to the wheels on a big-block Cobra after swapping the mufflers. He is very well-known in the Cobra field.
Jody
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