Jasper

Lookin to purchase a CAT back system to replace the stock, wondering what size pipe to use, a 2.25" or 2.5" system???

thx

Tranquilized

2.25"

andyy

u may loose low end torque if use 2.5"......

Jasper

I figured id be better of goin with a 2.25" exhaust system. But i see alot of 2.5" out there available for our car so just thought id varify.

Thanx again.

Jasper

Roddimus Prime

if you're only going to get a catback get it as large as you can...your manifold and both cats are much larger restriction than you'd ever need. If you get a full "race" exhaust then I'd suggest about 2.25 or so

Jasper

any other inputs?? all suggestions welcome....
im gonna be doin intake and exhaust. dunno if ill bother with the headers or anything to that sort. just getting some ideas. after that ill be lowering it with some coilovers i figure...

kcidmil

Well I would say 2.5" If you're going to be doing other goodies like a CAI. Then your exhaust will already be setup to handle the flow.

andyy

here is a header i saw someone is using~ and not expensive
http://www.cardomain.com/memberpage/338732/3
http://www.obxracingsports.com/perfo...=3&subcatID=22

check it out~ P.S, dont order from "essential speed", they never send my header(i've been waiting for 5 month)

Jasper

so now ive got 2 for 2.25" and 2 for 2.5" anyone else wanna break the tie??

GNO

2.5" will offer enough flow for over 300hp. My soon to be 11 second car has 2.5" pipes.

If you plan on getting a turbo, then go with 2.5". If not, 2.25" will perform much better for you.

TIEBREAKER - - - 2.25"

VagaBond-X

i think 2.25" would be the best if you are staying naturally aspirated

if you are going forced induction (turbo, supercharger) then go with 2.5"- 3" depending on how much boost you planning to run (alot of boost then bigger pipes) but 2.5" should be good enough for most forced induction applications, while keeping it to low boost.

but as i don't see anything about forced induction, i say go with 2.25"

Jasper

I dont really plan on goin forced induction. No plans for turbo or supercharge which is where i figured the 2.5" would have been better. But for the application im workin on ill stick to the 2.25" Thanx alot guys.

ooosirkooo

The better of the 2 will always be 2.5. Why? because of the principles your exaust works on. You see the exaust is like a straw and your engine in blowing the bad soke through this straw and out the back. So anybody knows that the exaust can oly escape as fast as it can go through the smallest point of the piping (This means the lager the straw the more flows through it) Your not going to loose any tork, because you dont get tork from backpressure. the faster your car can expell the used gasses the faster it can suck in more air, increasing the speed this accurs will only improve the efficiency of the engine. A smaller 2.25, will still be good because your results get better the more you elevate the HP, if your running stock everything & piping it out at 2.50 the 2.5 will be better thain 2.25 but the diference will be so insignifigant that it wont matter. Its only when increasing the HP you will need to increse the level of flow through the exaust. Everything will have better better results (CAI, CAMS, HEADERS ect.....) So if you plan to mod your car @ all get the 2.5 for best results, (and the coment that was posted stating the 2.5 is good for over 300hp is incorect, the HP level of the vehicle doesnt dictate the required diameter of the piping. It does dictate the level of catalytic converter you will need but thats irelevant. For the piping HP levels dont matter (if they did the exaust on a decked out Skyline would have to be 7 inches as the HP is arount 900. but in the end its your choice good luck.

Jasper

anyone else care to add to ooosirkooo's comments?? much fact or fiction in his little explaination????

GNO

Backpressure will not help with torque, however, exhaust velocity will. Exhaust velocity contributes to the scavenging effects, which in turn assists in torque output. Volumetric flowrate is a function of velocity and cross-sectional area. Given a fixed volumetric flowrate, an increase in cross-sectional area will yield a decrease in velocity.

If tuned accordingly, HP and volumetric flowrate are directly proportional. However, in street applications peak HP shouldn’t be as much of a concern as what is under the torque curve.

Once again, it all boils down to how far you plan on taking the vehicle. The difference will be minute, so if there’s a good chance that you’ll be building it up with higher compression or forced induction, then go with 2.5”. If you plan on racing regularly and will be spending a lot of time in the upper rev range, then again 2.5” would be better. However, you’ve already stated that FI is not in the plan and it doesn’t sound like you’ll be using the vehicle as a full-time racecar, so I will continue to recommend 2.25”.