BackDraft side pipe hp/backpressure mystery to be solved Saturday

Jimbocobra · #1 (**permalink**) 11-19-2009, 02:24 PM

I am heading to the dyno over the weekend to make a couple runs with and without the side pipes back-to-back, no tuning between runs. I want to see how much restriction there is on the standard pipe.

I spoke with Reg, he was told me to expect 2% hp loss. If that's the case, may not be worth new pipes, (9 hp for $2,000) I will post the results.

I did see these new Backdraft pipes - you can remove the baffling - very interesting...Side pipe

Zoom This · #2 (**permalink**) 11-19-2009, 02:34 PM

Be sure you keep an eye on your A/F ratio when you run open pipes. Your results can be skewed if the motor leans out and HP drops off.

Bill

Randy Rosenberg · #3 (**permalink**) 11-19-2009, 02:38 PM

Bill's right! I swapped my stock SPF pipes for one's with 3.5" ID mufflers and race collectors AND I made no carb changes - at 4kRPM is started sputtering - obviously running too lean.

If you want to make apples-to-apples comparison, then you will have to re-tune your carb (richen) to compensate for the decrease in backpressure.

Good luck,
Randy...

Jimbocobra · #4 (**permalink**) 12-01-2009, 03:12 PM

To close the loop on this post, it is 3% to 3.5% with a Roush 427 and was answered by naitive1 in the following post: Dyno Sheet - HP and Torque Question

mtpockets · #5 (**permalink**) 12-01-2009, 03:30 PM

I just removed my stock BDR side pipes and replaced with Cobra Paks. Rejetted up two sizes and now we're off to the Dyno. Sounds much better, this motor has to be breating better, the stock pipes are really restrictive. I'll post the results.
Before:
KC-408w, motor dyno'd 554hp/552tq
RWHP: 419.7/430tq
BDR #621

Jimbocobra · #6 (**permalink**) 12-02-2009, 06:37 AM

I'd like to see if you have a similar (3%) or so loss in hp. Some of the manufactures of aftermarket pipes are touting anywhere between 50-100hp. For me, that would be worth the trouble, but for 15 hp(3.5%) probably not.