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Forced Induction Forum Sponsored by Active Autowerke
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Old 10-14-2011, 07:40 PM   #1
diablorojo
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Any non M's with 3" exhaust?

I originally had a Borla exhaust ( prior to forced induction) that has been modified after FI to add an X pipe and changed the muffler also because the rasp was so bad. Now I'm considering going with a 3" custom exhaust but concerned about loosing back pressure.

I know it's common on the M to go to 3" but the exhaust set up is different.

Does anyone have any success with a 3" exhaust?
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Old 10-14-2011, 07:41 PM   #2
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Also...I have over 400rwh....
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Old 10-14-2011, 09:10 PM   #3
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Shitty video and wheels. 3" single on an NA motor. Do it.
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Old 10-14-2011, 09:11 PM   #4
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And another. Magnaflow 3" mufflers. A 14" and 18".
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Old 10-14-2011, 09:25 PM   #5
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I have dual 2.5 from header to exhaust. I'm wondering if I should do 3" dual to exhaust...
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Old 10-14-2011, 09:53 PM   #6
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The dual 2.5 outflows a single 3 area wise, but a single pipe is much easier in terms of muffler selection and whatnot. it also cuts down on rasp.
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Old 10-14-2011, 10:09 PM   #7
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I have 3" all the way to the rear muffler which is 2x 2,5" , my car is too quiet lol
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Old 10-14-2011, 10:14 PM   #8
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I'm looking more so because of boost. I'm thinking I can move more exhaust with dual 3" exhaust but wonders if anyone has done it with a 330. Are the M3's using dual 3"?
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Old 10-15-2011, 08:58 AM   #9
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The bigger boosted m3s use a single 4". You'd be hard pressed to fit dual 3 under your car, and honestly that's too much... unless you've got a worked over 572 under the hood.
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Old 10-15-2011, 12:43 PM   #10
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Im on turbo. My exhaust is 2.5" downpipe into a full 3" custom catback (Magnaflow 24" resonator and a 3" single inlet/ dual 2.5" outlet muffler). With the turbo it's not loud at all. Just a deep tone.

I strongly recommend it, especially if you are over 400rwhp. You get better scavenging effect (not back-pressure) out of a single big pipe than 2 small ones (when have you ever seen a high power supra or RB-powered Skyline with dual pipes? lol). People too often confuse the two terms. What you WANT is good scavenging effect (which for turbo is mostly useless, but for NA and blower setups yes you want it), what you DON'T want is back-pressure. Back pressure is literally a "backup/ clog in the piping" that robs power.
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Old 10-15-2011, 12:53 PM   #11
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@95blkmax....is it duel 3" from the header or single 3" from the header?
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Old 10-15-2011, 01:17 PM   #12
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Quote:
Originally Posted by diablorojo View Post
I originally had a Borla exhaust ( prior to forced induction) that has been modified after FI to add an X pipe and changed the muffler also because the rasp was so bad. Now I'm considering going with a 3" custom exhaust but concerned about loosing back pressure.

I know it's common on the M to go to 3" but the exhaust set up is different.

Does anyone have any success with a 3" exhaust?

the 700rwhp Turbo M3's run 3 inch downpipes....... so 3 inch all the way is plenty.
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Old 10-15-2011, 02:00 PM   #13
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I do, but no FI. Made good power over dual 2.5.
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Old 10-15-2011, 04:22 PM   #14
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I have a short section of 3", maybe a foot long, that then flares out to 3.5" to the rear tip

edit:

Quote:
Originally Posted by diablorojo View Post
Also...I have over 400rwh....
what do you have?
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Old 10-15-2011, 05:48 PM   #15
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I have 2.5 all the way to the muffler which meets 2.5 into the muffler and 2.5 out. I have an x pipe Borla resonators and a magna flow muffler.

Situation: I just got the head ported, larger throttle body and 14psi pulley (all going on over the next couple days). I'm going to have a significant increase in engine flow and believe I can benefit from a larger exhaust.

I'm thinking now of just doing a single 3.5" from the header to the muffler. I want to make sure I'm allow enough flow for an efficient exhaust.
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Old 10-15-2011, 09:17 PM   #16
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Quote:
Originally Posted by diablorojo View Post
@95blkmax....is it duel 3" from the header or single 3" from the header?
single 3" from the downpipe backto the muffler

Quote:
Originally Posted by aggieE46 View Post
I do, but no FI. Made good power over dual 2.5.
sounds about right . I had a 95 Maxima with a 3.5 swap, and I picked up about 7fwhp (NA at the time) going from single 2.5" to single 3".

Quote:
Originally Posted by diablorojo View Post
I have 2.5 all the way to the muffler which meets 2.5 into the muffler and 2.5 out. I have an x pipe Borla resonators and a magna flow muffler.

Situation: I just got the head ported, larger throttle body and 14psi pulley (all going on over the next couple days). I'm going to have a significant increase in engine flow and believe I can benefit from a larger exhaust.

I'm thinking now of just doing a single 3.5" from the header to the muffler. I want to make sure I'm allow enough flow for an efficient exhaust.
you will hate 3.5" exhaust. Thats overkill at your power level. A 3" mandrel bent exhaust with a non-baffled mufler (such as most magnaflow muffler) and a big resonator is more than enough for that.

Would you make more power with 3.5? Im sure you will.
Will it be an increase that will be worth the MUCH higher cost and the drone that you will not be able to get rid of?... well that's up to you .

Just trying to save you some money, headache, and the hearing of you and your neighbors lol
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Old 10-15-2011, 10:24 PM   #17
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I'm aiming at ~350whp for my next setup and will be running a 3.5" exhaust. I've seen gains on ~300whp naturally aspirated S54 motors by switching from 3 to 3.5.
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Old 10-15-2011, 10:26 PM   #18
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I'm aiming at ~350whp for my next setup and will be running a 3.5" exhaust. I've seen gains on ~300whp naturally aspirated S54 motors by switching from 3 to 3.5.
basic physics, math proves this isn't needed. I'd love to see dyno's? Did they switch Y pipe placement? What else was modified to see these gains? I suppose s54's defy physics to achieve this, I'm impressed!

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Old 10-15-2011, 10:45 PM   #19
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Search for any competitive S54 powered racecar, and see what exhaust setup they're running. The AA, Bimmerworld, and VAC S54 race exhausts are all 3.5" shortly after the header. A good amount of the e36 turbo guys have also found within the last couple years that upgrading to a 3.5" exhaust from a 3" has proven gains, a few of them are even going up to 4".

And what math and basic physics do you have that proves that a 3" will flow as well as a 3.5" for that application?
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Old 10-16-2011, 06:58 PM   #20
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Search for any competitive S54 powered racecar, and see what exhaust setup they're running. The AA, Bimmerworld, and VAC S54 race exhausts are all 3.5" shortly after the header. A good amount of the e36 turbo guys have also found within the last couple years that upgrading to a 3.5" exhaust from a 3" has proven gains, a few of them are even going up to 4".

And what math and basic physics do you have that proves that a 3" will flow as well as a 3.5" for that application?
+1 I love it when people say this and then don't spell it out. If it's so basic why wouldn't you just at least dish out the relevant formulas for those who are savvy and then explain relationship of the variables for those who don't understand "basic math and physics"
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