Dyno numbers with and without cutouts

[1969mach1351]

With mufflers: 307 hp, 315.5 tq
Cutouts open: 316 hp, 326.5 tq

That’s 9 hp and 11 tq. I didn't think there was going to be that much difference between the two. I have 2 chamber Flowmasters, dumped. The tech guy said that Flowmaster is one of the more restrictive performance muffler. My graph only starts at 3500 rpm and there is more power at 3500 with the exhaust open, I dont know if I'm losing any power at lower rpm.

 

[mustangdave]

Peak numbers don't mean anything. How was the area under the curve. Also, you may see more power from the mufflers if you ran a full exhaust; that's what they were designed for,

 

[TrickStang37]

ive NEVER seen a car make more power with a full exhaust vs. dumps. and yes, two chamber mufflers are pretty restrictive. in my 5.0, my car made more power from 3200 - 6200 with the cutouts open vs. full exhaust with 2 chambers. It made 331 rwtq @ 4400 vs 320rwtq @ 4400 with them capped. pretty much the WHOLE powerband. I remember it making 16rwhp more at 5700rpm (295rwhp vs 311rwhp) peak and at 6000 it was 18rwhp vs. them closed.

 

[ForceFed70]

Interesting!

I figured they would give more power... but was thinking less than 5hp/tq.

 

[thehueypilot]

Maybe it's not the mufflers but the multiple bends and crimps in your exhaust system that make it so restrictive?

 

[1969mach1351]

There are no bends in my exhaust. It goes straight back from the header into the muffler, I dont have tail pipes. There might be about a 15 degree bend for it to clear the tranny but thats it. The tailpipes I had have 90/180/90 bends in them, I can see how that would be restrictive. I would think there would be even bigger gains for someone running a full exhaust setup.

 

[Jc69Stang]

Thats good info to know, I was considering those electronic cutouts but wasn't sure, now I may just do that, and plus the noise/fear factor as well!