Disadvantages of 3" exhaust?

[cortrain]

I know, with some of my Honda friends that running a 3" exhaust will result in some power loss (race application). Wasn't sure if this was mainly a result due to tuning or not having forced induction.

Reason being I'm planning on FI-ing my FRS in a couple years but, Im buying the exhaust this year and don't want to have to buy it twice. Does anyone have experience with a 3" exhaust on their NA FRS/BRZ? If so, any feed back? It won't be getting tuned until next season, will that play a role?

Or, Should I just get a 2.5" exhaust now and cross that bridge when I get there?

This is my first time actually getting into engine work on a vehicle, I mainly just do suspension tuning.

Thanks guys.

[08stiguy]

From my understanding you get more low end torque with a smaller diameter pipe on a NA car. Larger piping gives you more torque in the higher RPM's. Reason, back pressure.

[cortrain]

Makes sense, so in my racing application a 3" would yield a better result because I'm in the upper RPM range.

[08stiguy]

Originally Posted by cortrain

Makes sense, so in my racing application a 3" would yield a better result because I'm in the upper RPM range.

Correct.

[JOSEC]

I don't know which part you mean to have 3 inch. But right now, I have JDL UEL mated to a 2.5" overpipe. It then crosses to a 3" Catted frontpipe, then 3" Catback. I myself is planning on a supercharger. But this works for now. It is quiet noisy without the main Catalytic converter.

[cortrain]

Originally Posted by JOSEC

I don't know which part you mean to have 3 inch. But right now, I have JDL UEL mated to a 2.5" overpipe. It then crosses to a 3" Catted frontpipe, then 3" Catback. I myself is planning on a supercharger. But this works for now. It is quiet noisy without the main Catalytic converter.

In theory I was thinking of the JDL 3" Overpipe/Frontpipe (catless) with a catted UEL header (For noise reduction) with a 3" Catback exhaust. However, Im just concerned with power loss for the couple years I don't have the SC. If that is even an issue.

[Kiske]

Originally Posted by cortrain

In theory I was thinking of the JDL 3" Overpipe/Frontpipe (catless) with a catted UEL header (For noise reduction) with a 3" Catback exhaust. However, Im just concerned with power loss for the couple years I don't have the SC. If that is even an issue.

You will NOT notice anything daily. Your car will however be much louder which may have a placebo effect into "faster."

[08stiguy]

Originally Posted by Kiske

You will NOT notice anything daily. Your car will however be much louder which may have a placebo effect into "faster."

Loud is right. I have Borla UEL with a 2.75" ISIS OP, DC Sport front pipe and a 3" Tsudo CB exhaust. Loud doesn't begin to describe it hahaha. I love it though. Loud isn't for everyone but it doesn't bother me.

[JOSEC]

[ame]http://youtu.be/OsV9DuG9XcM[/ame]

3" Disadvantage: Very Loud with anything Catless. I love the power gains but the volume level is something that I need to get used to. Already ordered an Ultra Quiet Front Pipe from JDL to fix some of that rasp. As for gains, I don't think you'll feel any difference between a 2.5" and a 3" while NA. Now if you don't mind the noise and you don't want to get another exhaust when you go boost, then a 3" exhaust now will save you money.

[cortrain]

Doesn't sound TOO loud, a catted header may help me for noise as well. I need that for emissions here, I figure I can swap out the front pipe with my stock catted one easy enough come E-test time.

As per power gains, I know they will be minimal until I get a tune and header.

Thanks for the responses guys!

[Freeman]

I've got a JDL UEL with a nameless performance 3inch catted and resonated OP/DO combo with a helmholtz resonator paired to a resonated 3inch Perrin Performance catback. Before I had my supercharger I noticed a loss in low end torque but a gain in the upper RPMs..... And tons of noise. I was the slow loud guy on the road. You can get a lot of performance out of a 2.5 inch, and not be the rolling joke on the road.

[cortrain]

Originally Posted by Freeman

I've got a JDL UEL with a nameless performance 3inch catted and resonated OP/DO combo with a helmholtz resonator paired to a resonated 3inch Perrin Performance catback. Before I had my supercharger I noticed a loss in low end torque but a gain in the upper RPMs..... And tons of noise. I was the slow loud guy on the road. You can get a lot of performance out of a 2.5 inch, and not be the rolling joke on the road.

Thanks for the perspective. Im just uncertain of how much more power I can achieve from 2.5" and a 3" once supercharged. If its minimal i'll be happier to go with a 2.5" and get some torque around town. Plus it'll increase the options I have for a brand.

However, I haven't been able to find the difference between similar set ups perhaps i'm not looking hard enough lol

Any feedback on the performance difference between the 2.5 and 3" once SC'd?

[robr]

Originally Posted by cortrain

Any feedback on the performance difference between the 2.5 and 3" once SC'd?

I installed/tuned a Vortech kit with a TRD exhaust (is that even 2.5"?). I don't have the dyno handy, but it was ~250rwhp IIRC. That's the only supercharged twin experience I have, sorry.

As to 2.5" vs 3" on forced induction twins in general, eh. You *will* make more power with the 3", but we've tuned multiple cars with 300+rwhp on both sizes. So, unless you're looking to get every last bit of power out of your setup, pick whatever exhaust you like best.

To put it in perspective, my car is conservatively tuned to 360rwhp with a 3" downpipe, overpipe, and testpipe, then goes to a 2.75" catback (minus the cat, of course). I can assure you the 2.75" parts are not as big of a bottleneck as you're thinking. Will I make a little more with a full 3" exhaust, yes. Do I care? Not especially.

Also, we just tuned an AVO car with whatever size the AVO downpipe is and made 398rwhp. Pretty sure he had a 3" catback though. The owner was asking about making a 3" downpipe, so he most certainly doesn't have a full 3" setup.



And yes, a complete 3" exhaust on an NA twin is obnoxiously loud. It won't be much quieter with a SC either.

[cortrain]

Thanks Rob, that's exactly what I wanted to know! Now it back to sound clips... lol