[Mannix]

Sound comparison and dyno comparison.

The biggest restriction in the exhaust system, I believe, is the cat. If that's true, then removing the cat should give the most gains.

What is the next biggest restriction to remove? For the N55, there are no secondary cats. So that's off the table. Resonators? Not sure. I took a peek under my car and didn't see any. Of course, I could have missed them. So that leaves mufflers.

A low restriction muffler (or set of mufflers) should free up some power, right?

Here are some claims:

AE Always Evolving Cat-Back Exhaust: +18WHP/+13WTQ

Billy Boat Axle Back Exhaust: Sport 10 HP and 12 TQ gains @ the rear wheels, Touring 8 HP and 9 TQ gains @ the rear wheels

BMW Performance Exhaust: up to 5hp and 3 ft-lbs of torque at 6600 RPM

HKS Downpipe-Back Exhaust: +11whp / +8wtq

Magnaflow Cat-Back Exhaust: +10whp/ +15wtq

Vanguard Cat-Back Exhaust: +11HP & 10 Ft./Lbs

Dinan: +6 hp @ 6600 rpm, +5 ft-lb @6600 rpm

What are the differences between these? The shape and "resonance" of the muffler probably isn't critical, since the turbo kind of "smooths out" the exhaust pulses. I would assume some mufflers flow better than others. And presumably, they all flow better than stock. But can they really improve flow so much to free up 10 hp? Especially with the stock downpipe in place? Replace the stock downpipe with a catless downpipe, and we should really be able to see how much of an improvement these mufflers provide, right?

Let's find out...

First the sound comparison:

Now the Dyno:

[mike@x-ph.com]

Keep in mind that -/+ 10 whp is within the dyno margin of error. Just because manufacturers advertise a 10 whp gain does not mean you will gain 10 whp


Gains are from the downpipes only

[maxihari]

Nice thread. Interesting perspectives.
Also please comment on sound.

[Cory S]

Looks like I am ripping off my Dinan exhaust....

J/K... I love it..

[BKBMW335I]

Glad I didn't waste any dough on this exhaust, i wonder if this is the same for "ALL" exhausts??