Exhaust size - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

jarednoel · 03-22-2015, 09:57 PM

Curious on what size exhaust everyone is running. Currently running a 2.25" exhaust but I'm wondering if it would be okay when I go FI with the SBD kit or if it's necessary for a 3". I'm aware of the bigger gains/better breathing exhaust but I'm just curious about the end of the spectrum that uses stock/oem exhaust piping, etc etc.

Thanks again!

robr · 03-22-2015, 11:44 PM

That small will choke a turbo down for sure, but 3" isn't "needed" unless you want crazy power. I really wouldn't suggest a 2.25" though.

I have a 3" downpipe and over pipe and whatever else you want to call the pipes before where the cat would be. Then I go to a 2.75" exhaust all the way to the back from where the cat would be. I make 360 rwhp at 11psi.

2.5" turbo back will support 300rwhp just fine as well. Routinely see 250 rwhp on full 2.5" setups.

mrk1 · 03-23-2015, 08:35 AM

SBD doesn't have a 3" down pipe so running a 3 inch exhaust wouldn't make that much sense. Larger diameter exhaust is most beneficial at the turbo end of the system.

robr · 03-23-2015, 02:01 PM

What mrk1 said is correct about turbos liking the bigger pipes up front. To that point as well, we did an AVO kit with their down pipe (2.5") to a 3" catback. Did 390rwhp at 1 bar. So even a "small" 2.5" downpipe will support a decent amount of power.

A Vortech with all factory exhaust parts, including cats, and TRD muffler did 260 or so, I don't remember exacts right now. Would it have made more power with larger exhaust pieces? Sure. But they aren't needed.

So really, it depends on what power you're hoping to run (I know nothing about the SBD kits).

xxscaxx · 03-23-2015, 03:02 PM

Keep it as big as possible near the turbo side, and stay on the smaller end from the catback if anything. I'll be running 3" downpipe/overpipe/midpipe to my 2.5 catback, not worried about the bottleneck as much as noise lol.

kbogarto · 03-23-2015, 04:03 PM

What is the stock exhuast diameter?

cdrazic93 · 03-23-2015, 04:26 PM

2.25 I believe.

I would correct some people's posts on here, but i dont want to start an argument.

Remember fullblown made 743whp on the stock exhaust.

protpibe · 03-23-2015, 07:43 PM

Quote:

Originally Posted by cdrazic93

2.25 I believe.

I would correct some people's posts on here, but i dont want to start an argument.

Remember fullblown made 743whp on the stock exhaust.

That's crazy! Do you have a link to that?? I just assumed they were running a 3" dp straight pipe

robr · 03-23-2015, 08:52 PM

Quote:

Originally Posted by cdrazic93

I would correct some people's posts on here, but i dont want to start an argument.

If you mean me, "argue" away. I don't get internet butthurt. My point was that a 3" isn't needed. I would never suggest trying to push 300hp through the stock exhaust, but I have no doubt it'd physically work.

And yeah, I assumed that FB car was running at least a 3" turbo back, if not open after the downpipe. Crazy.

mrk1 · 03-23-2015, 09:10 PM

There are also variables, a 2.5 exhaust with a straight path design will flow a lot and support some nice numbers. Also if you run a external waste gate dumping to atmosphere that's a large volume of gas that does not need to be handled by the exhaust. Yes I know SBD doesn't support a EWG but that's a draw back of the kit.

03-22-2015, 09:57 PM	#1
jarednoel Senior Member Join Date: Jul 2013 Drives: Asphalt Location: SoCal Posts: 239 Thanks: 41 Thanked 36 Times in 32 Posts Mentioned: 2 Post(s) Tagged: 2 Thread(s)	Exhaust size Curious on what size exhaust everyone is running. Currently running a 2.25" exhaust but I'm wondering if it would be okay when I go FI with the SBD kit or if it's necessary for a 3". I'm aware of the bigger gains/better breathing exhaust but I'm just curious about the end of the spectrum that uses stock/oem exhaust piping, etc etc. Thanks again!

03-23-2015, 08:35 AM	#3
mrk1 Senior Member Join Date: Mar 2013 Drives: Sterling BRZ Ltd Location: New England Posts: 1,702 Thanks: 403 Thanked 1,389 Times in 671 Posts Mentioned: 21 Post(s) Tagged: 2 Thread(s)	SBD doesn't have a 3" down pipe so running a 3 inch exhaust wouldn't make that much sense. Larger diameter exhaust is most beneficial at the turbo end of the system. __________________ The Build Thread GT28RS - eBoost2 - 3.91 Final Drive - Supra LSD

03-23-2015, 02:01 PM	#4
robr Senior Member Join Date: Sep 2014 Drives: 2013 FRS, with boost by ATS Racing Location: Haslet, TX Posts: 195 Thanks: 20 Thanked 82 Times in 58 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	What mrk1 said is correct about turbos liking the bigger pipes up front. To that point as well, we did an AVO kit with their down pipe (2.5") to a 3" catback. Did 390rwhp at 1 bar. So even a "small" 2.5" downpipe will support a decent amount of power. A Vortech with all factory exhaust parts, including cats, and TRD muffler did 260 or so, I don't remember exacts right now. Would it have made more power with larger exhaust pieces? Sure. But they aren't needed. So really, it depends on what power you're hoping to run (I know nothing about the SBD kits). Last edited by robr; 03-23-2015 at 10:08 PM.

03-23-2015, 04:03 PM	#6
kbogarto Senior Member Join Date: Nov 2013 Drives: 2013 BRZ limited WRB Location: Jacksonville, FL Posts: 120 Thanks: 135 Thanked 43 Times in 31 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	What is the stock exhuast diameter? __________________ 92 240sx (sold), 03 350z (sold), 13 BRZ (AVO turbo)

03-23-2015, 04:26 PM	#7
cdrazic93 Junior Join Date: Aug 2013 Drives: a car Location: Probably at school Posts: 4,341 Thanks: 3,184 Thanked 2,512 Times in 1,502 Posts Mentioned: 20 Post(s) Tagged: 0 Thread(s)	2.25 I believe. I would correct some people's posts on here, but i dont want to start an argument. Remember fullblown made 743whp on the stock exhaust. __________________ "Ah! What music! They could have never imagined, those pioneers who invented the automobile, that it would posses us like this, our imaginations, our dreams. Men love women, but even more than that, men love CARS!"-Lord Hesketh

03-22-2015, 11:44 PM	#2
robr Senior Member Join Date: Sep 2014 Drives: 2013 FRS, with boost by ATS Racing Location: Haslet, TX Posts: 195 Thanks: 20 Thanked 82 Times in 58 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	That small will choke a turbo down for sure, but 3" isn't "needed" unless you want crazy power. I really wouldn't suggest a 2.25" though. I have a 3" downpipe and over pipe and whatever else you want to call the pipes before where the cat would be. Then I go to a 2.75" exhaust all the way to the back from where the cat would be. I make 360 rwhp at 11psi. 2.5" turbo back will support 300rwhp just fine as well. Routinely see 250 rwhp on full 2.5" setups.

03-23-2015, 03:02 PM	#5
xxscaxx Senior Member Join Date: Jul 2012 Drives: 2013 SWP BRZ Location: New York Posts: 2,240 Thanks: 458 Thanked 878 Times in 556 Posts Mentioned: 34 Post(s) Tagged: 0 Thread(s)	Keep it as big as possible near the turbo side, and stay on the smaller end from the catback if anything. I'll be running 3" downpipe/overpipe/midpipe to my 2.5 catback, not worried about the bottleneck as much as noise lol.

03-23-2015, 09:10 PM	#10
mrk1 Senior Member Join Date: Mar 2013 Drives: Sterling BRZ Ltd Location: New England Posts: 1,702 Thanks: 403 Thanked 1,389 Times in 671 Posts Mentioned: 21 Post(s) Tagged: 2 Thread(s)	There are also variables, a 2.5 exhaust with a straight path design will flow a lot and support some nice numbers. Also if you run a external waste gate dumping to atmosphere that's a large volume of gas that does not need to be handled by the exhaust. Yes I know SBD doesn't support a EWG but that's a draw back of the kit. __________________ The Build Thread GT28RS - eBoost2 - 3.91 Final Drive - Supra LSD

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