So my local exhaust shop says that he could install an axle back system with a muffler and tips at a fair price. Since it is axle back that means it would mate to the OEM pipe which is 2" or 2.18" if I remember right. My question is if I went CAT BACK and increased the pipe size to 2.5" would I see any appreciable gains from doing so? I could see going to 3" and gaining something worthy but I don't want/need 3". So is it worth going to 2.5" or just stick with axle back and save some money? FYI I would be installing the magnaflow muffler #12265. Cheers!

 

If you plan on future mods, then yes upping the tubing size will help. How much all depends on all the mods you do.

 

I don't plan on more than a CAI at this point. *Maybe* muffler delete. So changing the pipe size to 2.5 would not do much if that's all the mods I want to do? Thanks braminator.

 

Unless you plan on a tune and a bigger turbo there wont be enough of a difference for you to feel IMO.

 

Tune or no tune having a 3" pipe over a 2.5" will give you a significantly better flow and create less restrictions for your turbo. Anyone with the All4 might not be able to go with a bigger pipe because the drive train takes up the space the non-All4 uses, which allows for the 3" pipe all the way back.

I've noticed less lag on the turbo because of the exhaust specifically.

 

Even exhaust makers like Milltek and Magnaflow use a 2.5 inch exhaust. going to a 3 inch can cause a power loss down low and only gain on the high side and increase noise.
For your reading pleasure.
http://www.magnaflow.com/02product/s...ayproducts.asp
http://www.millteksport.com/exhaust....3#.UYm7rcph68A
http://www.exhaustvideos.com/faq/how...pipe-diameter/
http://www.tercelreference.com/terce...st_theory.html

 

Cool, I'll check these out.

 

A Cat-back exhaust gives you nothing...

 

We did a bunch of testing when we built our custom exhaust and found no gain with the 3inch over a 2.5inch. We actually lost a little torque, mainly cause the exhaust gas velocity dies with the 3inch.

 

I second that.

 

But are there real gains to be had from 2" ----> 2.5" i.e. stock pipe size? THanks

 

Cat back.... no.

 

Way-
Was all this testing done on a stock mini or did it have bolt-ons , tune, bigger turbo .. etc ?

 

i have a milltek 2.5 inch DP back on my 2012 all4

there is another 2012 all4 in town that is speced like mine

with both all4s fully stock, doing rollons from 1500 rpm , both stock, we were axle-2-axle all the way to redline

after i installed my milltek (only mod on the car), same road, same 1500 rpm rollon, i am ~5 car lengths ahead at redline

my buddy says all the gain is below ~4500 rpm, from ~4500 to redline i am not pulling away any more

i have not dynoed the car

scott

EDIT: ALL ROLLONS DONE IN 3rd GEAR

 

Good info , nothing like good old drag racing proof...lol
I'm sure you guess where not speeding right ??...lol

 

it was not a drag race ... a rollon takes driver skill put of the action ... besides, with all the clutch woes I read about I NEVER do a drag start

 

• Quote:

  Originally Posted by Melangell

  A Cat-back exhaust gives you nothing...

i disagree ....


a second cat back may not get any gain, but my milltek downpipe back gained me 5+ car lengths against another similarly equipped CM all4 in a 3rd gear roll on from 1500 to 4500 rpm


before the milltek, we were axel to axel, after the milltek, and only changing the exhaust, NO other mods, i was visibly faster


so that mysterious person "everyone" that "knows" there is no gain from an exhaust is wrong!