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!

 

[jonk00000]

What will happen to my o2 sensor ??

 

[leet]

There is a bung on the piping to thread the O2 sensor into.

The only thing I don't like about those O2 eliminators is that if you just want to pull the DP off, it is more difficult.

 

[soul]

There is a bung on the piping to thread the O2 sensor into.

The only thing I don't like about those O2 eliminators is that if you just want to pull the DP off, it is more difficult.

yea thats def true....but mines not that bad and I use an evo8 oil filter, the stock oil filter is impossible to get off without dropping the exhaust.

 

[bigemrich]

Oil Filter Relocation

--Kyle

 

[tstkl]

i know this is going to sound like a stupid question, but do the o2 eliminators eliminate the precat as well, or can you still pass emissions with one?

 

[ericbev]

i know this is going to sound like a stupid question, but do the o2 eliminators eliminate the precat as well, or can you still pass emissions with one?

Any aftermarket DP will eliminate the pre-cat and leave you with the main cat at the rear of the car... as for emmissions.. not too sure but id guess that you would pass just fine...heres a thread that would be of some help http://www.dsmtuners.com/forums/showthread.php?t=155448

and I can remove my oil filter just fine with my buschur DP

 

[Omega]

We don't have a precat. I asume you refer to the flex coupling that is needed? If so, then no, the flex coupling is still there.

 

[c5chris]

We don't have a precat. I asume you refer to the flex coupling that is needed? If so, then no, the flex coupling is still there.

Yes, the 2G do not have pre-cats.

There are 2 kinds of O2 eliminators: one that dumps to the atmosphere and one that dumps back to the downpipe. The one that dumps back to the DP may pass the sniffer test but not visual. But if you live in Cali, anything other than stock will fail smog.

 

[na_turbotalon]

I have a 3" O2 housing with a 46mm wastegate on it with a dump. It makes everything such a pain in the ass. I miss the days I had a tiny 14b on there. Absolutely no boost creep or spikes though so it's doing a good job.

 

[dsm dominator]

i will be running 15-18 psi on my stock turbo

could i get away with stock piping but high flow muffler and cat?
or would i just be needlessly robbing my car of a signifigant amount of horsepower?


if so what do you recommend?


thanks

--scott

 

[BaddAssGst]

definitely get an exhaust. you would be robbing your car's horsepower badly. if your not going all out, just get a 2.5" turbo back. If your not planning on doing anything super fast, there is no need to get a 3". But an exhaust... is always a good idea.

 

[dsm dominator]

thanks for the help

 

[planblars]

i would get a full 2.5" 3" if you are planning on getting heavier into modding....i would also not turn your boost past 15psi until you get a few more mods on your car 18psi seems a bit high for what you have done right now especially with the stock exhaust

 

[mic84]

i went to a local muffler shop.told them about my car and the guy working there said that my 2g eclipse can only take 2.25" catback exhaust system(talking about magnaflow). i've searched on this site and most of the people here haf 3". the guy said that if i were to put on a 3" it will be scraping the road as i drive.i'm like what the hell?...a lot of ppl have done it. so,wat do u guys think?..sorry for the noob question.

 

[IHeartTurbo]

Go somewhere else.

 

[project_tsi]

hes afraid of doing it, tell him "well make the bends tight enough to the body and I wont have to worry about it hitting ground." or do what the other guy said and go somewhere else

 

[daren_p]

Ya the guy doesn't know what he is talking about. I run the Apexi N1 catback system on my car which is 3" and it goes under the rear crossmember (factory goes above but 3" wont fit). My car is lowered and I still have lots of ground clearance, I would say the exhaust is around 4" off the ground at the lowest point.

 

[97GS-TSpyder]

I had a N1 and scraped on everything. But it sounded good.

 

[mic84]

yea,mebbe i'll look somewhere else,anyways,thanks for the replies.

 

[yoshimitsuspeed]

(factory goes above but 3" wont fit). .

BS
I made my own and it fit just fine. Some don't because they are lazy bastards. I like driving dirt so I am very concerned with ground clearance, if I had someone else do it and they said they were going under the axle I would kick them in the balls. When I did mine I tucked it up nice and close to the undercarrige and I doubt I lost 1/2 inch in clearance.
Find someone who knows what they are doing.

 

[mic84]

u mean the pipe is bent nicely above the rear axles rite?..

 

[99gst_racer]

Yeah, almost all aftermarket 3" exhausts travel underneath the rear crossmember. This makes that area more prone to scraping the road on a lowered car. I have a good size hole on my GReddy right now. But many 2.5" exhausts are made to follow the factory piping route which is over the top of the crossmember.

 

[HSK]

3" can clear over the axle, just hammer in few inches into the spare trunk space.

n1 exhausts look nice tilted and slightly facing upwards, in over to achieve this look you have to go under axle. and you will scratch your exhaust and your piping now and then if you are lowered.

 

[yoshimitsuspeed]

3" can clear over the axle, just hammer in few inches into the spare trunk space.

n1 exhausts look nice tilted and slightly facing upwards, in over to achieve this look you have to go under axle. and you will scratch your exhaust and your piping now and then if you are lowered.

I didn't have to do a thing to my trunk space. The exhaust does tap the rear diff ocasionally but that's it. I didn't know tilted upward was the saught after look but mine does a bit.

 

[daren_p]

3" can clear over the axle, just hammer in few inches into the spare trunk space.

n1 exhausts look nice tilted and slightly facing upwards, in over to achieve this look you have to go under axle. and you will scratch your exhaust and your piping now and then if you are lowered.

Hmm, I haven't had my N1 scrape anywhere yet & I'm lowered about 1.6 or 1.7". You should be fine with the exhaust under the rear cross member because the part where its lowest is inline with the rear wheels so if you go over a speed bump etc. the wheels go over it and raise the whole car, still giving you the same clearance as if you were on flat ground. The only time where this would be a problem is if there is something sticking up from the road that wasn't big enough for the wheels to go over. Don't know if my wording makes sense, but I think you can understand what Im talking about.