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!

 

[shiftedtsi]

if your looking for only 300whp 2.5'' is fine don't lose sleep ova it pm'd

 

[shiftedtsi]

2.5'' full exhaust is fine for 300+whp dont lose sleep over it

 

[Booster-Shot]

Is there a major sound difference from a 2.5'' and 3?

 

[negativezero27]

i just really want to know sense i am keeping the STOCK muffler if i need to go with 2.5 or 3inch.

 

[noz]

i just really want to know sense i am keeping the STOCK muffler if i need to go with 2.5 or 3inch.

by any chance, do you know how restrictive the stock muffler is?

if you are keeping the stock muffler...i suggest you just go to a muffler shop and tell them to make you a 2.75" or 2.5" crush bent catback to the stock muffler....shouldn't cost more than a bill.

 

[cua0]

wow, i wish 2.5/2.75 crush was that cheap here.

i'm thinking of doing the same this week, i'm pretty sure my cat is plugged (288k km on chassis & probably exhaust too) i own part of a muffler shop and we can usually get away with about 200 for a crush bent system including resonator but not muffler, add a muffler and that's what you end up paying most for.

if i were to go 3" it would definately be mandrel bent stainless turbo back, replacing the stock o2 with a custom piece and go from there.
that's just me though, and i'm new to the dsm market. heh

 

[GSX6bolt]

2.5 straigh cat back exhaust... 3.0 just insnt neccesssary if ## wanting a car that can hit 300hp range.

 

[4geze63]

At that stage should the difference be noticable?

 

[fwdturbobov1996]

3 in. People run 3in when they have 250awhp and are fine with it, deffinatly 3 in. 2.5 would be to small I think. But I have no scientific facts to prove these other than that when you increase a 1/2 inch you add 4x that to the volume you can flow. Cuse your expaning 1/4 inch each side. Math is probably off on that,vaguely remember that.

 

[95blackGsTurbo]

Are you running a full 2.5" mandrel bent exhaust and going to go to a full 3" mandrel bent exhaust? I've run both on my car and there is a sound difference but as far as performance goes all's I got was more boost spiking. maybe 5-7hp or something around there but it wasn't noticable to me and my 1/4 mile time's stayed virtually the same. MAYBE 0.05 of a second better at the most. Differs from car to car though. I am on a big16g and I am reaching the limit's of it. What turbo are you running?

 

[Lordpaxin]

bigger is always better.
more flow out means more flow in.

3 inch flows better than 2.5

though it may creep a bit more than 2.5 get a full 3 inch with 02 eliminator.

 

[negativezero27]

seriously what is crush bent catback exhaust??? stock muffler is so much better IMO. Its annoying to hear your car when you are just crusing around with aftermarket exhaust. The only time i ever want to hear my exhaust is when i get on it, but then again my motor will be screaming plus my turbo.

 

[4geze63]

ported evo316g
all supporting mod and then some. I am deffinatly getting a o2 eliminator by RNR or VSR

 

[1993eclipseGS]

This topic is discussed about 3 times a week anymore. I did not even hafto leave the ''new thread'' page, And this was right under yours.

http://www.dsmtuners.com/forums/showthread.php?t=199515

 

[t0ny007]

bigger is always better.
more flow out means more flow in.

3 inch flows better than 2.5

though it may creep a bit more than 2.5 get a full 3 inch with 02 eliminator.

3" definitely outflows 2.5" but tell us something we dont know please.

The question is asking if there is a noticable difference.
On a 16g there might be a slight difference at 350whp but not that big of a difference, but i wouldn't go with anyhting smaller the a 3" catback if you get a 2.5" downpipe.

 

[Lordpaxin]

RNR 02 eliminators are good stuff.
ive had 2 of them 2g, and 1g.
this isnt an RNR discussion but expect a long wait. and perhaps some fittment issues that can be cleard up with bending the hangers a tad.

3 ich 02 elim on a evoIII 16g is great. youll love it. I had the same setup,
ported evoIII with 34mm flapper.

 

[tstkl]

bigger is always better.
more flow out means more flow in.

3 inch flows better than 2.5

though it may creep a bit more than 2.5 get a full 3 inch with 02 eliminator.

never talk....... ever again......

the only way to tell if the 3 inch full exaust system is too big is to get two egt gauges, one around the o2 seonsor or exaust manifold or downpipe, and the other near the tip (but not too close, because it will start picking up ambent air temps) and see what the drop in temperature is.... if its really big then you know that your engine doesnt have the power to get all that gas out fast enough and its just cooling down in your exaust, gaining density, and causing unwanted back pressure... SHORTER IS ALWAYS BETTER, NOT BIGGER....dumbass....

 

[Spaniel1287]

On my 2g Talon right now i got an intake, UICP, 1g bov. I ordered a 2.5" exhaust system, a walbro 190 fuel pump, and a Joe P MBC. With those mods, should I see quite a bit of increase in my 1/4 mile time assuming I turn up the turbo 2 pounds? Also on the way is a 14b turbo to replace the Hair Dryer T25. So my question to you advanced guys out there is this: Would a 2.5 full Exhaust, 190 fuel pump, Intake, UICP, 1g BOV, and 14b Turbo (at 15-16psi) get me around 14 on the 1/4?

(Keep in mind my 2g Talon is a FWD Automatic)

Thanks for the input.

 

[Lordpaxin]

Friend, your a retard.

though i wont get into a arguement with you. you must really think a lot of yourself.

 

[95blackGsTurbo]

Better watch it there chief. I would take Paxin's word anyday over your's. Even though his statement isn't completely true there is still no reason for that. And shorter isn't better because I have gone with a stock open downpipe and it boost spike's more than a full 3" system. I would never go with a shorter exhaust on a forced induction car. I was just saying with a 16g of sorts the difference won't be to noticable. Trust me I know from experience.

 

[94Jettameowpsst]

You will probably have a gain with the 3 inch for the simple fact that its less restrictive. But i've been told on numerous occasions that you wont outflow 2.5inch until around the 400whp mark

 

[hereitcomes]

ya that should do plenty for a 14. My buddy's TSi FWD ran a 15 flat with a cat back and about 9-10 lbs. hes a pretty good driver too.

....on the other hand my 2g N/T ran 2 seconds slower than stock and i have mods done...hah i suck at the track
GOOD LUCK

 

[1993eclipseGS]

There is NO way to tell unless you actually take the car to the track. I don't care what anyone says, You cannot guess a 1/4 time. My buddy with a ported b16g and supporting mods - the fmic/injectors, on race gas and 18 or so lbs of boost, ran a 15.1 in an auto car. There is NO WAY you can guess. Take the car to the track, And run. Every car is different, And So is every track/weather etc.

 

[larsenracing]

You may brake into the 14's.

 

[OSXer]

You may brake into the 14's.

I think that if he is using the "brake", there is no way that he will get into the 14s.