3 inch exhaust vs 2.5 inch with cutout

I posted this on tuners, but I am not getting any straight answers. I always try to post there due to sheer volume even though some of the posts are just childish.

So my intermediate pipe ripped in a perfect place to replace the broken section with a cutout. I don't care about noise, so I wanted to put a cutout between the cat and the muffler as a clamped cutout makes a very cost effective solution in this case. The existing cat is a hi flow catco and the muffler is a magnaflow. The existing exhaust size is 2.5"

How much less power will I make with this setup as opposed to a 3" setup with a muffler? (mind you both would be catted)

I can't imagine there would be a huge difference if any. I ask because I read that a 20g at higher boost is a no no with a 2.5 inch exhaust. This is why I went with an E316g but want to know if a 2.5 inch catted exhaust with a cutout would work out fine with a 20g at higher boost or not in case I ever decide to upgrade.

Thanks

 

Wont decimate ur power make make 5-10 less hp tops more than likely you wont even notice since you already running a cat

 

[EHmotorsports]

It all comes down to your power goals and how you want to achieve them. I work mostly with race cars so I'm all for squeezing out every ounce of usable power. So I would say go with the 3.0" if you have plans for more power in the future. More air that goes in the engine has to come out. If it has restrictions 2.5" may hinder performance. With that said if this is a street car I think you would be safe with what you have.

 

[mountaineerjeff]

when I did it, I did 2.5 exhaust, then did a 3" cutout that bypassed the cat. gave a noticeable reading on the butt dyno.

 

[5OF2k]

with turbo cars, generally they are extremely responsive to upgrades/modifications that help it breathe better. I have an E3 16G on my car as well as an e3 manifold and 02(ported) and full 3" turboback exhaust with a high-flow Magnaflow cat, and Im running about 26lbs.

Now, I had taken my exhaust apart at one point to service my driveshaft, and killed the gasket. Being as I decided to wait until a Sunday to do the work, I was unable to find an open parts store to replace the gasket I munched up upon separation of the exhaust(who knows how old the gasket was). In a nutshell, I was forced to run around for a couple days with open downpipe, and HOLY EFF was there a difference. And this was before I was running 26lbs regularly, it was only at around 18-ish. Boost creep=non-exhistant. Spool time drastically improved and WAY harder, and the higher end of the rev-range was a lot more powerful with less drop-off in boost/power than with the rest of the exhaust hooked up.

Basically what I'm trying to say, is keeping it at a 2.5 and running a cutoff will help and work, but upgrading to 3" would help more, IMHO.

Hope that helps!

-Jake

 

[blacksheep]

Jerkoff buschur did some test between 2.5" and 3" and showing 3" did not make any more power up to a certain hp and certain turbo or something. I don't remember

 

[DynastyLCD]

for what its worth, i ran 22 psi through an FPgreen in my GVR4 using a full 2.5" exhaust, with a high flow cat. it spooled rather quickly, but gains would have been had to goto a full 3" setup.

is the 20g you are running a TD05 or a TD06? if it's a TD05 i don't see why it would be much different than a 16g with the same turbine wheel.

 

[Ian M]

Both of my cars, seat of the pants wise, (on top of sounding like sh*t) feel like sleds with an open DP versus "3 turbo back,14b or 20g. Boost hits harder with through full exhaust,which may be deceptive of how hard the cars actually pull. Even if open DP was a little faster, unless I'm at the track seat of the pants fast is more fun.

 

[boostin4door]

3"

 

Lots of help here guys...not running a 20g...was just wondering if I'd have a hassle if I ever moved up. At this point, will just stick with the E316g then. Thanks alot for all of the ideas! Would like to see that research from Buschur on 2.5 vs 3 inch. I mentioned that once because someone mentioned it to me but was never able to get anything solid. I ended up getting the 2.5 inch cutout in the middle of the thread somewhere but feeling iffy about it. Oh well only $37 bucks and will still be better off than I was which was just fine.

 

[JNR]

definitely be good to confirm with a dyno/track time vs. SOTP feel, as IMO a louder exhaust could make everything *feel* faster and visa versa...a lot of it depends on your setup too and generally speaking a larger exhaust tube is better for higher rpm power and you want your turbo/cams/head/fuel/tune, etc to take advantage of that...I doubt it's going to make or break anything with using either a 2 1/2" or 3" exhaust (apples to apples) but on a dyno it may show some difference and may or may not be a more pleasurable experience (the noise, usable torque and so on).

I have a full 3" exhaust on mine with 2 1/2" DP and it seems to be a good size...the muffler is a smaller casing oval glasspack (like magnaflow, but it's not that brand) and it sounds good, as it's sort of deep and mellow at the same time, with a little bit of (liveable) drone. I want to try a turbo muffler instead though and imagine it'd sound even better, but full SS mufflers (rest of system is all 304, incl muffler) aren't cheap and too many other things to buy first.

 

Well I finally got it done. A bit louder but it works. Since I did it after the cat, may have not gained much but had to have gained since there is no longer a muffler. The cat does a pretty good job at muffling the noise.