midpipe question

[M4_lgnd]

i talk to a few guys and they were saying that a midpipe wont do any help and power gain. So is that true and how come?


thanks!

[135Pats]

Anything back of the downpipes is going to give you marginal gains, aftermarket midpipes and mufflers are 98% for sound and tone, from a performance standpoint they get rid of some back pressure/are lighter but that's about it. If you want more power from your exhaust, it's the downpipes that are going to do the trick, that's where the most restriction is to be found.

[theinfamousdrew]

Originally Posted by 135i_lgnd

i talk to a few guys and they were saying that a midpipe wont do any help and power gain. So is that true and how come?


thanks!

On your car, I wouldn't say there would much gain from it.

Now thats not quite the same for a N54 powered 135i.
The N54's have an extra set of catalytic converters in the midpipe.

Here is a side by side shot I took of the 2.
The ones on the left are from my 08 with the N54, the ones on the right are from a N55.
I replaced mine with these

[1speedbike]

I posted this a while back in response to a newcomer:

...

Downpipes will net you the most gains. Replacing the midpipes will net you slight gains since you're getting rid of the resonator and the two secondary cats, and upgrading the axleback (really, removing or upgrading the muffler) will probably net you 5 horsepower at most and is really done mostly for sound. The bigger the downpipe(s), the greater your gains will be, because you will have much more room for the air leaving the turbos which allows them to breathe a lot better. By the time the air gets to the axleback, it won't be nearly as fast or turbulent, so freeing up that section of the exhaust has the least gains. And as I said, the midpipes will net you moderate gains, especially in a 2008 N54 car since there are secondary cats in the midpipes for those cars and removing those cats will get rid of some restriction. I see you have a 2008, so in my humble opinion, AR Design and Macht Schnell make the best 3" downpipes, while Raceland makes decent quality 2.5" downpipes for a much cheaper price.

Hope this helps!

So the reason...



The air flowing through the downpipe section of the exhaust is the fastest, most turbulent, and hottest (therefore having the greatest volume by Charles' Law). By the time the air gets to the midpipes and then the axleback, it will have cooled off, contracted to a smaller volume, and will be flowing more slowly because a smaller volume of air is going through a pipe of constant diameter.

Because of this, removing restriction, minimizing bends, and increasing the cross sectional area of the downpipes is the best best for adding power. It's that air that needs it the most. The midpipes will net you some gains on an N54 car because you'll remove the restrictive secondary cats. Even on an N55 car, if you buy some quality midpipes that are slightly more voluminous and have smoother bends can add some power, but not much. By the time the exhaust gasses get to the axleback, though, they're moving pretty freely. Midpipes might net you like 10 HP at most if you're removing some cats in the process. Axleback might net you like 5 HP, as mentioned above.

[ken1137]

Originally Posted by 1speedbike

I posted this a while back in response to a newcomer:

Because of this, removing restriction, minimizing bends, and increasing the cross sectional area of the downpipes is the best best for adding power. It's that air that needs it the most. The midpipes will net you some gains on an N54 car because you'll remove the restrictive secondary cats. Even on an N55 car, if you buy some quality midpipes that are slightly more voluminous and have smoother bends can add some power, but not much. By the time the exhaust gasses get to the axleback, though, they're moving pretty freely. Midpipes might net you like 10 HP at most if you're removing some cats in the process. Axleback might net you like 5 HP, as mentioned above.

^ This should've been your 2,500th post Congrats BTW...I'll never catch you.

Yep, OP not much gain regarding performance. Find a good tune and add the supporting bolt-ons to gain a shit-storm of power

[1speedbike]

Originally Posted by ken1137

^ This should've been your 2,500th post Congrats BTW...I'll never catch you.

Lol, when did you join? June 2011... so you've had a little over a year for 1400 posts. Took me 4 years to make 2500! You'll have me beat by 2013 as long as you keep it up

I'm sorry to hear about your 1er though. 335i is fun, but not the same. Still, kudos for being an adult and having a happy wife! Plus, it's basically the same car, just bigger. Lmk if you start parting stuff out

[M4_lgnd]

cool thanks for the info. saves me money too get my new wheels!