Does Size Matter? 2.5" vs. 3" Exhaust discussions. [merged]

[Boostin18]

2.5" vs. 3" exhaust discussions are merged here.

I have a 90 GSX and when i bought it the guy said it was full 3" turbo back with a EVO3 O2 housing (ported), now here is my question. When I took the exhaust down, it had a 2.5" exhaust flange at the top of the down pipe and then flares for about a half inch out to 3", if that makes any sense. This is my first 3" exhaust and I was wondering if this is right? I was thinking of porting the o2 housing because it is 2.5", making it 3". Then bringing the exhaust to a shop and having them weld a 3" flange to about a half inch long peice of 3" ehxaust pipe and then welding it on to the whole exhaust. So basically getting rid of the 2.5" flange and the half inch long flare and just welding on the 3" flange with the new piece. Would this make a diffrence if i do this or not. I don't know if this would make any diffrence or not, but when i put a boost controller on, i would try and get it to set at 15psi, but never would it would just spike and go down to like 12 or 13, but never above 15, but never at 15. I also have a ported 2G manifold (havent had it off to make sure it really is ported). Any help would be great!

 

[Boosted98RS]

i'm surprised your friend didn't boostcreep.

cutout's are retarded IMO, most people aren't not making enough power to outflow a 3" nevermind a cutout at the cat.

His ran better unless my car was heat soaking and it actually made no difference. But his car feels stronger when he opens the cutout even with the t-25 on it.

 

[blcknspo0ln]

His ran better unless my car was heat soaking and it actually made no difference. But his car feels stronger when he opens the cutout even with the t-25 on it.

I guess that's why we call it a butt-dyno

 

[dsm726]

alright well thanks for all the comments. The thing i want to know is what i need to do to get about 250 whp while spending the least amt of money. I have an intake, an hks ssq (no performance, i know), cat back 2.5 inch, a brand new small 16g turbo with no play, a brand new 2g manifold, an APT mbc (not homemade), an afc, an autometer boost gauge, and a motor that was just rebuilt. i dynoed it while it just had the filter and the cat back and it had 158.7 whp, and then the guys at logic performance turned up the boost on the awd dyno to about 13 psi and i was running 177.3 whp. they said that it shouldnt be turned up past 13 psi cause they were running the afr and thats where i started getting cut. any suggestions to get me to around 250 whp would be great thanks.

 

[Ludachris]

alright well thanks for all the comments. The thing i want to know is what i need to do to get about 250 whp while spending the least amt of money. I have an intake, an hks ssq (no performance, i know), cat back 2.5 inch, a brand new small 16g turbo with no play, a brand new 2g manifold, an APT mbc (not homemade), an afc, an autometer boost gauge, and a motor that was just rebuilt. i dynoed it while it just had the filter and the cat back and it had 158.7 whp, and then the guys at logic performance turned up the boost on the awd dyno to about 13 psi and i was running 177.3 whp. they said that it shouldnt be turned up past 13 psi cause they were running the afr and thats where i started getting cut. any suggestions to get me to around 250 whp would be great thanks.

Comparing your mod list to the stage 1 upgrade path...
http://www.dsmtuners.com/tuning-guide/1gturbo/stage1power.php

it looks like still need some fuel system upgrades (190 pump and rewire at least). And since you're at higher elevation, it may even be tougher to hit your goal with just those mods. You might need a logger and an S-AFC. I'd recommend getting your injectors cleaned. And make sure you test for boost leaks of course. 150whp on a 16g is nowhere near great, but you still have a few more supporting mods you need to do to prevent fuel cut - then you can turn the boost up a bit.

Oh, and put a stock 1g BOV back on there - sell your SSQ and you'll get some money to put towards mods that will yield performance gains instead of making loud noises. Venting your BOV isn't what you need if you're trying to squeeze out every ounce of power on a tight budget. Read up in the FAQ forum on why venting is not a good idea if you're interested in getting the best performance out of your car (and can't afford to get a MAFT).

 

[dsm726]

yeah thanks Ludachris for all the help. I definitely dont have my bov vented cause i know it runs like shi!. but im going to buy a 190 pump and a dp now. and i plan to buy some new injectors soon. I have to get my afc installed first tho.

 

[dsm726]

i was wondering if anyone knew where i could get a stock recirculation hose for a 1g. I have a hard plastic pipe on there now and it is kinked pretty bad and i want a straight through shot to the intake from the bov. any help would be great thanks.

 

[blcknspo0ln]

go to your local autozone with a mock setup.. and find a radiator hose with the same bends and diameter..

works everytime

 

[-DSM2NR-]

I've been running my downpipe open for over a week now. I don't really have problems with boost creep. It sounds both ricey and in some way like a v8 if you ask me(depending on the RPMs).
I got a 3" catback ready to install but the question is: do I even need it anymore? or will the open downpipe do just fine? And also, would I gain or lose hp if I was to bolt the 3" catback to the 2.5-3" downpipe?

 

[unlmtdndeavor]

the question is do you have problems with the local authorities with the noise your car is creating. if not, i say no.

 

[98eclipseRS]

the question is do you have problems with the local authorities with the noise your car is creating. if not, i say no.

Man all them trucks in nebraska gots to be louder than his car with open dp. I keed I keed, seriuosly though you don't NEED the catback but I can garuntee that it will get quite annoying after a while having just the open dp. As for how much power will be lost by putting on a 3" catback not much so I wouldn't worry about it to much.

 

[-DSM2NR-]

the cops don't seem to mind . I've driven past a couple of them and they didn't do anything.

Well I don't even know if you can consider it a "open downpipe". It is still connected to the exhaust but the bolts haven't been screwed all the way meaning, there's a opening between the downpipe and exhaust about an inch and there's no gasket so, would you even consider this a open downpipe?

 

[gridlyne]

You dont smell exhaust gases in your cabin? Cuz that might be a little bit on the dangerous side. I remember I had a leak around that area and the exhaust gases made my eyes burn! Just worry about your health and get the problem taken care of.

 

[xveganxcowboyx]

From the setup you are running now you'll probably gain power with a good down pipe and exhaust. You basically have a really nasty exhaust leak at the moment.

 

[-DSM2NR-]

I guess I'll fix it then. You can't really smell the gas inside the cabin. You can only smell it a little when the windows are open or you're standing outside but nothing major.

 

[oldman]

I guess I'll fix it then. You can't really smell the gas inside the cabin. You can only smell it a little when the windows are open or you're standing outside but nothing major.

Play responsibly, put the exhaust on, you can take it off at the track. Remember, you represent all of us out there.

 

[K_Hill]

You can't smell carbon monoxide so you wouldn't know if you was breathing it in!! I would put it back on cause after a while it would get annoying and it for sure wouldn't give you a good impression on the authorities around you. You can always take it off at the track..

 

[JaxTalonTSi]

I ran my RnR 3" downpipe open on my 1g for about a week and a half. The novelty of open downpipe wears off when you take a trip that lasts more than an hour, or everytime you get out of your car your ears are ringing. It also sucks for driving around neighborhoods at night. The final straw was getting a $75 exahust ticket from the Jacksonville Sheriff's Office.

But whatever floats your boat. I'll sooner run open 02 anyway if im a cheap bastard, its not as loud anyhow....

 

[97EclipseGS-T]

... My gasket from my N1 to the Downpipe burnt off once and I almost fell asleep at the wheel in broad daylight... I would definatly put it back

 

[paranoidTSi]

Good luck passing emissions and inspection. I also believe that adding a 3" catback exhaust will HELP performance instead of HURT it.

 

[talontsi902]

haha the open down pipe that is great i had mine off for about a month and thats how mine stude out from the other 4 talons that looked like clones


sounds like a freaking semi ill never go back to an open down pipe agine soudned realy cool when the turbo would spool up

 

[otownawdtsi]

i love open down pipe, but at the same time police dont so the best solution to me is run your 3" exhaust and get an o2 housing with an external dump ...sounds awesome but at idle sounds low and not quite as illegal...till you hit full boost

 

[my_precious]

i have a question about this. I understand that I could get into trouble with the police, but honestly, is running a down pipe bad other than noise and bad smells? I got a deal with my talon when I bought it a few weeks ago, but unfortunately it DIDNT come with exhaust or a turbo. i just sent a check out for a turbo and o2 sensor housing but buying a full exhaust system is out of the question for me right now. I could just wait to drive my car, but it might take awhile without a job. Point is, running a downpipe (i still have to buy one) vs a full exhaust would allow me to drive a few months sooner. what do you guys think?

 

[joshohatesuall]

i have a question about this. I understand that I could get into trouble with the police, but honestly, is running a down pipe bad other than noise and bad smells? I got a deal with my talon when I bought it a few weeks ago, but unfortunately it DIDNT come with exhaust or a turbo. i just sent a check out for a turbo and o2 sensor housing but buying a full exhaust system is out of the question for me right now. I could just wait to drive my car, but it might take awhile without a job. Point is, running a downpipe (i still have to buy one) vs a full exhaust would allow me to drive a few months sooner. what do you guys think?

the smell isnt as much of a problem as the carbon monoxide pouring into your car. one thing to consider is finding a used stock downpipe/exhaust to use until you can acquire the funds to buy aftermarket parts.

 

[my_precious]

i tryed that. i have found stock or 2.5 inch down pipes for 50 dollars or so, but for a full stock set up the cheapest ive seen is like 200-300. I have seen used performance 3in cat back set ups for that much. I could just plug up all the holes going into the cabin besides the windows, and have the windows rolled up all the time. Would that work?

 

[airmail96]

Are there boost creep issues associated with running open downpipe?