exhaust upgrade question
 

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

2.25"

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

thanx guys
 

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

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

2-2.25" and 1-2.5"
 

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...

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.

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)

ok its all tied up.. anyone else???
 

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

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.

:argue: TIEBREAKER - - - 2.25"

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"

Thanx guys, 2.25" it is.
 

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.

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.

interesting way of looking at it....
 

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

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”.

agreed that increasing the diameter of the piping will also increase the average path/crossectional area where air can pass, BUT BUT BUT, this is only if increased too much like 3 or 3.25, a 4 cylinder engine with a .5 increase in the piping will have no adverse efects & NO LOSS OF POWER, and the better flow will outway the loss of minute almost none existant so much so it will never be noticed,velocity, again 3 inch piping would have a more evedent efect but even with that it still would be hard to notic at all, but not 2.5. with that ther is only a .5 increase and that is not enough to cause problems. especi
ASWELL THIS STILL HAS NOTHING TO DO WITH THE HP OF THE ENGINE, but the egine leter size compression ration and a few other factors, but not the HP.

and in responce to
Quote:
Originally Posted by ooosirkooo
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.

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.

The volumetric flowrate is not proportionel to the cars hp no matter how you tune, here is a calculation to show what your volumetric flowrate is on your car

Actual volumetric flow rate (ft3/minute) is equal to MFK = Mass flow rate taken from Auto Tap log (lb/minute) OVER d2 = Density of air for the intake air (lb/ft3) there are other calculations for other types of engines and other ways to calculate it for your own engine, but this has no connectrion to the HP lever

So you can continue to sugest 2.25, but I DONT if the guy plans to do any mods, and if hes discussing increasing the piping system I would assume he plans to do other mods aswell. this will need the 2.5 pipe

The main reason, I recommend the smaller piping is becuase this isn't a race car. Personally, I like to have more low and mid range power where I spend the majority of my driving at.

:cookoo: Do you drive? If so, you're probably familiar with the accelerator pedal. The further you press it down, the more power the engine produces. The accelerator pedal is directly linked to the throttle. The throttle controls the volumetric flowrate. How is this not directly proportional to horsepower?

in all actuality GNO is correct. Backpressure does NOT equal torque. PROPER exhaust gas flow promotes scavaging which promotes torque.

Also, someone else said it earlier and it's basic physics: Just like with an intake, you can have 4" piping all the way down the length of the car but if your muffler has a 2" outlet you're only going to flow that 2"s. Your smallest restriction is going to be your biggest inhibitor. I have a header that meets at a 2.5" collector...it then plumbs into a 2.14" stock midpipe...after that it wouldn't matter how big my catback was....I'm NEVER going to flow anymore air than that 2.14" mid-pipe.

If you are designing a FULL exhaust from header back then YES you may only want a 2.25" exhaust since you're going to control the ENTIRE flow of the exhaust.

Does this make more sense?

Original poted by Roddimus Prime

"in all actuality GNO is correct. Backpressure does NOT equal torque. PROPER exhaust gas flow promotes scavaging which promotes torque"

I never stated diferent, I number 1, I stated backpressure DOESNT CREATE TORQ, yes proper exhaust gas flow promotes scavaging which promotes torque, but increasing the pipe diameter by that .5 WILL NOT CREATE IMPROPER exhaust gas flow, (only if exadurated there will be a adverse afect ) so the coment is pointless.

I comented that If full pluming go 2.5 (and I still DO state go for 2.5), and thats ofcoarse from headers out, and if you plan to Turbo the car I sugest 3 inch all the way., As for the other coment

"Also, someone else said it earlier and it's basic physics: Just like with an intake, you can have 4" piping all the way down the length of the car but if your muffler has a 2" outlet you're only going to flow that 2"s. Your smallest restriction is going to be your biggest inhibitor. I have a header that meets at a 2.5" collector...it then plumbs into a 2.14" stock midpipe...after that it wouldn't matter how big my catback was....I'm NEVER going to flow anymore air than that 2.14" mid-pipe.
"

It was ME THAT SAID THAT!

So your telling me Im wrong on details I never disputed, verry interesting.



Anyways we can sit here and argue all we want, but know this Turbo mag has a MS protege (with the tiny turbo and they instaled 3 inch piping from the Downpipe back, and got 22.1 added HP, so argue all you want, but Dems de breaks, a tiny tiny stock turbo with 3 inch pipes will give 22 extra HP Think about that and the mods you plan to do, but if you plan to do anything real you have my sugestion

ooosir, firstly shut up with your attitude. No'one said you were wrong about anything. I only said GNO was right....and he is.

secondly, english must not be your first language so I'll let the horrible use of grammar and spelling slide but you need to pay more carefull attention to the way people word things.

lastly, If you honestly believe adding a 3" exhaust to a MSP will add 22whp then you are insane. They added a fuill exhaust, intake, front mount intercooler, etc and got 22whp increase. Ithink they even got 12whp from the intake if I remember correctly.

Turbo's do want as free a flowing exhaust as possible but even if you remove the entire exhaus from the cast exhaust housing and run nothing you wont get 22whp. I hate to burst your bubble. Don't be a "bench racer".


p.s. no'one here gives anyone a hard time so the attitude is not needed nor welcome.

Listen up In reguards to Turbo mad they got the 22 from the piping and also got 12 from the intake and FMIC, but , the hp level was below what the manafactuer braged (somewheres around 158whp) and they brought it up with the intake reflash of the ECU, and FMIC, and only then did they add the exaust and got 22 HP, you want to get fresh over a simple argument I was trying to be nice and argue my point of vue, go check there site they will confirm it,. SO keep your 2.25 and eat my exaust fumes PUNK!


FROM MACDADDYSLOMO: consider yourself censored and warned...your foul mouth will not be tolerated

canadians,......sheesh. Guess where this one wound up?

hahaha
 

hey I am canadian lol hahha I take offence, but ummm now if he was french canadian, hahah by all means, hahah go right ahead attack the quebec'r lol hahha

Dang!
 

Cous! All of that language was not called for! you must not know who you were talking to! You off da chains homeboy! It seems that someone needs some pussy! Roddimus did not try to start a fight, you lost your cool get it together. All in all, if the exhaust is too big it will cause turbulence which disturbs exhaust flow and slows down the pace of exiting gas. And when that happens the effect that is looked for has been defeated. So that is why he said keep it 2.25 because if we can all take a minute to recap, the man who started this thread said that he did not want to go turbo in the furture. So keep it real and lets try not :wtf: to belch all we know in one sentence. Which we found out was not too much.

Well I didn't get the thumb that rodimus posted but DUDE! Thats messed up, your showing your self and it don't look cool!
As far as the size, I just sold my truck and I could us the same advice, I need a good cai, header, and a good size exhaust. I will be doing nos if I have enough left over.
I am learning a lot about these 4 bangers from you guys. But I spent 9yrs in the military and I don't need a lesson on being a potty mouth!
So any good critisium (Yea I know I cant spell, I don't need to I learned how to kill instead LOL)would be nice.

sounds dangerous I will not be messin wit you. LOL

GNo you rock....thought I'd have to do the stupid backpressure is not beneficial arguement...but you've got it handled quite nicely! Give him a cookie!! :chug:


explanation of the pic...band = banned...as in gone from the site :o

He's gone, I left the post up for those who may have thought I jumped to conclusions on that guy. My first post to him was a stern warning which he didn't want to take seriously. I love this forum and it's friendly helpfull members. Let's all keep it that way.

Back on topic. Hughes, I reccomend the Ebay CAI, Obx 4-1 header and catback of your choice. If you're planning on using N20 start a seperate thread about it when you're ready. I have good advice for you and even a nice dry kit for sale if you're interested.

yup he is french quebecore lol

Now I get it!

4-1 header??? i read somewhere that a 4-2-1 header would be a better selection for an overall performance result... was this information incorrect??

as for teh whole muffler size and only being able to exhaust as much air as the smallest pipe.. i realize that, but he intake and exhaust is only a beginning upgrade, eventually im considering doing a header and high flow cat as well.... that being said is a 2.25" exhaust system still my best bet?

i appreciate all the input u guys are giving me, im not a big car person so im learning alot, and i apologize for some of the trouble my thread has caused and id like to finish off with saying that not all us canadians are bad people :P lol