3" vs. 2.75" vs. 2.5" exhaust - North American Motoring


3" vs. 2.75" vs. 2.5" exhaust

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Old 10-19-2016, 09:03 PM
toyopet toyopet is offline
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3" vs. 2.75" vs. 2.5" exhaust

I've been in the market for a downpipe back exhaust and was leaning toward the AWE because of the sound. However, the 2.5" diameter tubing seems too small.

I noticed many aftermarket exhausts for 2.0L engines have 3" mandrel bent tubing. I was wondering why most manufacturers of F56 aftermarket exhausts are using 2.75" rather than 3". And AWE is using 2.5".

I understand most of the gains are due to the removal of the secondary cat. I think the larger diameter piping would also result in additional power.

What are your thoughts?
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Old 10-20-2016, 10:00 AM
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johntotah94 johntotah94 is offline
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To my understanding. Smaller tubing increases the velocity of the gasses and keeping turbo response. Removing cats are the important part. 3inch is over kill.
Even on my Stage 3 R56 with a 45mm turbo, I had a 2.5in exhaust.
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Old 10-21-2016, 11:37 AM
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Josh/AWE Josh/AWE is offline
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There is a few good bits of info in this thread, as well as why we went with 2.5": https://www.northamericanmotoring.co...ml#post4154614
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Old 10-21-2016, 10:58 PM
Sall4Ken Sall4Ken is offline
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I ran a 3.5 on my high hp evo x there really wasn't much difference besides sound and better increase in top end at high rpm but I never put it on the synopsis after upgrading. I agree with the above its overkill and will probably even make it feel sluggish in certain areas of the power band unless it's a pretty high hp mini. This was the 3.5..


Regular sized spray paint can
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Old 10-22-2016, 05:11 PM
toyopet toyopet is offline
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Quote:
Originally Posted by Josh/AWE View Post
There is a few good bits of info in this thread, as well as why we went with 2.5": https://www.northamericanmotoring.co...ml#post4154614
I read that thread awhile ago and what stood out is what ryephile posted:

Some OEM information on the different B48 states of tune:

Cooper S exhaust is 60mm
JCW exhaust is 70mm
BMW 730i (high tune B48 w/ 258 HP and 295 LbFt) exhaust is 80mm in the midpipe and 75mm aft.
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Old 10-24-2016, 12:31 PM
honderpilot honderpilot is offline
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I custom build my 2.75". Let me know if you have any questions about power/sound/anything
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Old 10-24-2016, 11:01 PM
isamin isamin is offline
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3 INCH piping will give your sound volume and in return it will take away your low end torque. Bask in the sounds of power as the wimpy fiat 500 blows you away at the lights.

ISAMIN
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Old 04-14-2017, 10:38 AM
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This is an older thread but what the heck.


Think of the exhaust diameter as the final step in dialing in your power band. Assuming no significant change in the volume of air though your engine, a larger diameter pipe slides the power band range higher in your rpm's.


Using a totally HYPOTHETICAL example,
say your power band with stock exhaust is 2500 to 5500 with redline at 6000.
1) increase exhaust diameter stock+0.5 inch
result: power band is 3500 to 6500rpm (redline still at 6000)
2) decrease your exhaust diameter stock-0.5 inch
result: power band is 1500 to 4000 rpm


3) increase exhaust diameter stock+1 inch
result: power band is 4200-7000 rpm (again redline still 6000)


To be clear, this is with no significant change to the volume of air though the engine.


Obviously if you change the volume of air through the engine with +boost, bigger turbo, whatever. THEN increasing exhaust diameter is required IF you want to keep the same rpm power band range.
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