Motordyne M370 bust
 

So I had bought a used M370 plenum hoping to get some gains as far as torque is concerned. I was aware that a little loss in top end power was the general consensus judging from what I was reading around here. It was paired with my Motordyne ART pipes, Takeda Long Tubes, and Ark catback. I was tuned with mustang dyno at 282whp and 244 tq before the install from JTRAN Motorsports before they closed shop. After the install, I had tuned at Kozmic Motorsports and actually lost power and tq at 262whp and 214tq. I decided let's put the stock back on, retune and call it a day. Ended up making more power than what JTRAN had made but a bit less tq (295whp and 233tq). So now I'm selling my M370 and going for Z1 Ported Stock Plenum. Hopefully it turns out better.

was the retune done on the same day..

Nope all tunes done different days.

then that is probably why the difference in power.

U mean with kozmic's tune on both Motordyne and stock? Or JTRAN's tune with stock plenum vs Kozmic's tune with stock plenum?

I have m370 as well but i did not lose any power. After tune i made 320ish (up rev) it might be ur tuner or something else.

Dyno runs on different days can be a huge difference in power made.

^ weather can make a big difference in numbers. You should look at the graphs to see which is better under the curve. Horsepower sells cars, but torque wins races.

I was told by a certain tuner of note that neither plenum would produce worthwhile gains and he essentially said a modified plenum wasn't worth it.

You're right. Just got back from my retune after I installed my Z1 ported stock plenum and Motordyne catback (not that it matters). Only picked up a few ponies. Attachment 127781

At least it appears you gain across almost the entire rpm band. Does the motordyne catback have larger piping than the ark you originally dynoed with?

Yea I'm happy i got gains. The Motordyne plenum wasn't doing anything for me. The ark runs 2.5" all the way. The Motordyne catback runs 2.5" to 3" from the cat to the tail.