We just built a 402 recently(there is a thread about the motor) and got some open vs closed dyno number with our 4 " electric cutout. This is a 402 with 1 3/4" HVMC headers our 3" Off Road Y Pipe going through a 4" Mufflex Catback with our 4" Quick Time Electric Cutout.

We wanted to see what gains would be on what is thought to be one of the best catbacks out there.
10.5 HP Gain Peak
12 TQ Gain Peak

15HP and 18.4TQ Gain at 4300

And it averaged 9.9hp gain and 10.8 TQ gain. Averaged!

Enjoy
RPM HP Closed TQ Closed HP Open TQ Torque HP Diff TQ Diff
3100 234.2 396.8 236.9 401.3 2.7 4.5
3200 246.1 404.0 248.1 407.1 2.0 3.1
3300 260.6 414.7 258.7 411.7 -1.9 -3.0
3400 272.6 421.1 269.8 416.7 -2.8 -4.4
3500 284.8 427.4 284.2 426.5 -0.6 -0.9
3600
3700
3800 318.4 440.0 327.2 452.2 8.8 12.2
3900 326.0 439.1 338.4 455.7 12.4 16.6
4000 336.3 441.6 349.6 459.1 13.3 17.5
4100 347.8 445.6 360.9 462.3 13.1 16.7
4200 362.3 453.1 375.5 469.5 13.2 16.4
4300 376.7 460.1 391.7 478.5 15.0 18.4
4400 391.6 467.4 405.4 483.9 13.8 16.5
4500 405.6 473.4 418.7 488.7 13.1 15.3
4600 414.3 473.1 429.9 490.8 15.6 17.7
4700 425.3 475.2 437.4 488.8 12.1 13.6
4800 433.9 474.8 446.1 488.1 12.2 13.3
4900 440.7 472.3 452.2 484.7 11.5 12.4
5000 447.1 469.6 458.5 481.6 11.4 12.0
5100 453.6 467.2 463.6 477.4 10.0 10.2
5200 460.9 465.5 472.4 477.1 11.5 11.6
5300 464.1 459.9 476.9 472.6 12.8 12.7
5400 470.8 457.9 479.4 466.2 8.6 8.3
5500 473.4 452.0 483.0 461.2 9.6 9.2
5600 476.8 447.1 490.7 460.3 13.9 13.2
5700 484.3 446.3 497.4 458.3 13.1 12.0
5800 490.8 444.5 501.0 453.6 10.2 9.1
5900 495.1 440.7 505.7 450.2 10.6 9.5
6000 495.4 433.6 505.9 442.8 10.5 9.2
6100 476.6 410.4 490.8 422.6 14.2 12.2
Avg Gain 9.9HP 10.8TQ

 

Barry, your thread is just in time. I am planning on upgrading my exhaust soon. I lose approximately 18 rwhp between open headers and a fully closed exhaust. Even with your 3" cutout, I still lose 6 rwhp compared to open headers (with extensions). I look forward to trying out the 4" cutout on my F-Body in the near future.

 

How about some soundclips.

 

I lost 26 rwhp and 29ftlbs going through a mufflex catback vs. open cutout on my heads cam car.

 

yup, my 4" mufflex robbed me about the same.

 

i have a set of 3" qtp's to go on my new setup with a 4" mufflex, i'm interested to see what my gains are with my new 421" motor.

 

4" mufflex catbacks are terrible this is no suprise to me. thats why I hacked off my muffler and put in a magnaflow race muffler hehe. Of course I am also using your 1-7/8s LTs with dual cutouts, but they are just for sound, I ran 9s with them closed, but I should try with them open, not sure it will make that much of a difference until I get to the 900 hp level.

 

Have any soundclips nick?

 

I have a 3" Y into a flowmaster merge 3"-4" over the axle and through a dynatec split flow oval. It put down 461/408 last dyno. So maybe mufflex doesnt make them very well, but I made mine from scratch and it is pretty close to theirs. I might put extensions on and see what the difference is.

Brandon

 

sure.

http://www.blackssei.com/nick/NickN997Small.wmv

 

 

sounds sweet

 

yea the spintech muffler used in the 4" catbacks rob lots of power. Try swapping mufflers and retesting the cutout?

 

with the the 3" i gained 16 hp would i see more with the 4"?

 

I Don't think it is so much the size of the exhaust as it is the muffler itself being the restriction.