Whats the deal with AFE's new 3" exhaust for the 3.6? Is 2.5" not enough? It's kinda funny how AFE posts dyno numbers for the 3" but not the 2.5".

 

Quite frankly I don't see how any of this matters without an ECU tune. The stock ECU tune will cancel out any intake and exhaust gains over time.

 

A 3" single exit exhaust is too large for the 3.6L Pentastar. However the 2.5" stock exhaust is nominally too small. 2 5/8" would be the appropriate size if there was such an animal, while running smaller will increase low end torque but limit high end horsepower and larger will reduce low end torque while possibly increasing horsepower in the upper rpm range. Best to just leave it at 2.5".

 

I would say your spot on. 8.4 liter Dodge Vipers and 7.0 liter Corvettes only use 3" exhaust, cant find one bigger for those cars, dont know how a 3" exhaust would apply to this tiny motor? A loss of a ton of low end torque is what I would expect.

 

The Viper/Vette use dual exhaust, where as the JK uses a single. A 3" doesn't seem way to big for a 285hp engine. I agree w/o a tune it may loss a bit of low end tq. Oh & thanks AFE, I just installed the 2.5". Why does AFE make 3 different exhaust for the 3.6?

 

Yep if it were a race car, the rig with a 2.5" exhaust would have a quicker 60' time and lower ET. The rig with a 3" exhaust would have slower 60' times, a lower ET but more mph at the finish line.

Given that these vehicles spend a lot more time in the lower rpm range, there isn't an advantage of having a larger exhaust.

 

Thats true, I forgot the JK doesnt have dual Exhaust Still probably to big for a 3.6. Maybe with a tune and 5:13 gears, wait a minute, I amy have to try that!

 

If we 3.6L's ever get a tune.

My new AFE exhaust special order lol:

 

Jpop,

Can you explain the advantages of a single vs a dual (not a true dual, just single muffler and dual exit), and also explain cat-back vs axle back?

 

Exhaust velocity slows after the split which reduces the amount of scavenging. In effect, it slows down the exhaust through the entirety of the system and mitigates pulling spent fuel from the cylinders. There's a pretty fine line between getting peak exhaust gas velocity and having restriction. A freely flowing exhaust system doesn't necessarily make more power as a too large of a system will not scavenge any spent fuel in the cylinders. Leaving some spent fuel in the cylinders limits the amount of fresh air and fuel that can be induced on the intake stroke, limiting combustion.

There are a bunch of online calculators for exhaust sizing that can be of benefit. The formulas work pretty well, in fact excellent, until you get into blown or turbo applications. My experience comes from some drag racing and of course some trial and error failings. In the end, I've always had better results with exhausts that leaned towards the small side, they're quicker and have better low end torque which is ideal for a street driven vehicle. Also, just to clarify smaller is quicker, bigger is faster, if that makes sense.