Exhaust Size
 

Sorry if its been talked to death but I really couldn't find an actual answer.

If I have no immediate plans of going FI in the near future but possibly in a couple of years down the road, does one exhaust size actually produce more NA power than the next?

I was looking into the Q300 because I would prefer something on the quieter side, but if another exhaust is going to produce noticably more power I would consider it.

If all your going to change is the catback it won't matter much. The factory header is the most restrictive part of the exhaust system. If your doing headers etc... 3" i believe is the loudest and makes the most power but your only talking about a few whp difference between 2.5" and 3" if your NA.

2.5" is fine. I personally have the Q300 and Invidia catted front pipe with a catless JDL UEL header. It's really tame and sounds great, but very very mellow inside the car. Larger piping may produce a slight HP increase but in higher RPM's. Suffers at lower RPM's.

Q300 is a great choice for staying quiet, but it can still be heard when you get on it. I have an N1 on the way to test loudness/rasp with my setup. Don't care too much about drone as much as I do rasp. Either way, I'm keeping my Q300 as a backup. It's a wonderful catback for anyone looking for a quiet, well performing exhaust that has a nice straight feed to the muffler with very few bends. Burnt titanium tips are a plus on ultramarine and they're priced nicely too.

Somewhere around an additional 10-30 wheel HP and 15-20ft-lbs more torque with 3" compared to 2.5" (with tune) according to perrin's dyno testing.

And it doesn't "suffer" in lower rpm's as stated above, it has no loss of power or torque anywhere. It's just more noticeable in the higher rpm range.

http://blog.perrinperformance.com/3-...ults-and-tune/

I would take that with a grain of salt... Many of those are inflated numbers. Dezoris dyno'd a full Perrin headerback on a stock tune and gained a couple WHP, lol.

I had a full 3" exhaust and it felt like the very low rpm's from a stock to like 1200 rpm was boggy due to the large exhaust. At 4k+ rpm though, it felt great. It's just too raspy at 3" with NA. 3" is definitely meant for a turbo and much higher HP numbers in the 500+ range. 2.5" can withstand upwards of 400 whp just fine. I would recommend 3" on a turbo only and not N/A because the few horsepower you gain, for one, is not noticeable, and two, the noise is horrendous unless you have a track car.

Yep I agree, all of your research should be taken with a grain of salt. Seems like the difference in your experience and the article would be the tune.

But I don't think I've ever heard someone described a 3" perrin system as raspy though. Louder, yes, but raspy, not so much. If you replace the headers with catless then yea it might get a bit raspy, but I'm pretty sure OP has stock headers correct?

To answer the OP's question though, it all depends on what your definition of "noticeable power" is. The 3" will give slightly more hp/tq than the 2.5" but most would consider it not a very noticeable difference. So it would come down to an extra ~$150 for the 3" parts and you'd get a small bit of extra hp/tq and a bit louder exhaust. Good luck with your decision though, hope this info helped!

Im planning on doing a full header back, and if I did FI it would be a supercharger so I wouldnt be going crazy on the WHP figures so it sounds like 2.5 may better suite my needs.

I was thinking the Q300 simply because Ive had good experiences with Invidia in the past and figured I wouldn't run into fitment issues if I went invidia all the way up to the header.

If a tune is only netting an extra ten whp I dont think I'll be too concerned...Thanks for the help.

There's a video of the Borla UEL on the 3" resonated Perrin system. It has some rasp because the pipe size is so large even with that giant resonator.

Last question, how are these 3 inchers mating to the front pipe? Do they taper?

Gasket. The flange size is still the same. Some differ though, my 3" had a donut gasket with two long screws to mate it to the midpipe. My 3" downpipe hooked up to a 2.5" header flange with no problem. I just used a 2.5" gasket on that one instead of a 3" to seal it.

For n/a on the street 3 inch is silly.

I'm running an N1 with a catted Invidia FP, JDL Overpipe, and JDL UEL. Nice deep sound like a WRX, has a little drone, but nothing like a stock header. Loud, but not overbearing like a 3". I love it.

My Q300 is sidelined if for some reason I decide I want it back on. The N1 sounds incredible though.

vids or false.















jk

lol, I'll work on an idle/rev one tomorrow. No GoPro for the awesome videos. :(