Exhaust Piping Size Debate

[ArunSenior04]

There is a huge debate on what muffler sizing to use. People on here say that 2.25 is good for our motors, while "experts" say that its too much for our simple low hp n/a motors.

So my question is, for stock, what is the best size?
150Hp size?
200HP size?

[Cypher]

well.... turbo 2.5" is good for up to like 300whp...

[PSUsouthpaw]

2.25 is more than adequate for a N/A car. While 2.5 will help out at high revs, it will cause you to lose lots of low end torque. 2.25 with crush bent is decent, but mandrel bent is the best. Unless you are doing serious modding, like big shots of nitrous or higher compression pistons, you likely will not hit capacity of the 2.25 size.

Stock I believe is 2.00 crush bent.

[evan938]

stock is 1 7/8 crush bent. like i said in the other thread, if you got 2" mandrel, you basically paid 160$ to get a new muffler put on. 2.25" mandrel is going to show the best gains

[ArunSenior04]

Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car. Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. 4 bangers in the 150-200 hp range should go 2-2.25 inches, turboed and v6's in the 200-250 hp range can go 2.25-2.5 inches. For engines making 250 to 350 hp, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches.

[evan938]

reece. please stop posting information that is incorrect. you DO NOT need a 3-3.5" exhaust for 250-350hp

[ArunSenior04]

How is 2.25 going to show the best gains for out n/a low hp low hp to the ground cars? Has ANYONE dynoed the car with 2" piping, and then with 2.25" piping, to show a HUGE gain in performance? Nope. Even with a catback exhaust, you arent seeing tons of HP gains. (5 or less HP. )

reece. please stop posting information that is incorrect. you DO NOT need a 3-3.5" exhaust for 250-350hp

says who tho?

[evan938]

people have dyno'd 7-8 whp from a good cat back. heres what i was looking for. if you doubt it, write corky bell. writer of maximum boost

http://mahonroy.home.comcast.net/turbo/exhaustd.jpg

[ArunSenior04]

Reading the graph, at 200HP you should have 2.25 in piping. Our cars have 120HP to the wheels.

Shoot according to that graph, we should only have about 2 1/8.

[evan938]

maybe yours does. im at or just above 140. remember that with exhaust and headers, not only does it free up HP, it opens the exhaust up a bit more, allowing the engine to rev faster. this helps a lot more when you get things like pulleys that allow the crank to spin a bit faster, it will need that extra room in the exhaust to expel the gasses.

your exhaust is so close to being 2" crush bent exhaust (only 1/8" smaller) that you having them make you a new 2" crush bent exhaust did close to nothing. next pipe size up is going to be 2.25". what do you think makes more sense? add an exhaust thats 1/8" bigger and wont flow much better, or get the 2.25" exhaust that will free up some flow?

i wasnt using the graph to show you where OUR exhausts should be at, as it starts at about 150hp. this is made from a writer writing about high performance engines, turbo kits, superchargers, etc. what i was using it for was to show you how misleading your engines making 250 to 350 hp, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches.statement is

[ArunSenior04]

But even if you're pushing 140HP, according to the graph, 2.25 is still too large of a pipe according the credible source.

[evan938]

right, but the graph also shows that a good size for 140hp is about 2". thats 1/8" bigger than stock size. obviously the 2.25" exhaust helps our car out quite a bit or it wouldnt be dyno proven AND every exhaust manufacturer wouldnt be using 2.25" mandrel bent exhaust piping

[ArunSenior04]

But just because the pipe is bigger, that doesnt mean that bigger pipe = better performance.

[evan938]

ok. lets do this. anyone who has a stock xd, get a 2" exhaust made. ill pull my intake, put the stock header back on, and put my GT wheels back on, and we'll go dyno. evofusion 2.25" vs 2".

[Cypher]

also... keep in mind that graph was made for turbocharged applications... in turbo car you need a bigger exhaust because backpressure = bad. because you can get overboosting/boost creep whatever you wanna call it. thats what the graph is for. i thoguht stock exhaust was 1 3/8s?

[ArunSenior04]

Sounds good, because by that graph, 2.25in is too big.

Taken from http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

Pipe Sizing
We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust. Ah, the drawbacks of horsepower. The best alternative here would probably be to just run open
exhaust!

[evan938]

no. 1 7/8

[Cypher]

yup so you're right evan. foudn it in one of troy's posts. "the stock piping is 1.875" OD and press bent with very restrictive mufflers as well, so it will be certainly an increase in diameter, velocity, etc." but its a press bent (which is same as crush right?) so the actual flow is probabyl like 1.5? or so. so 2" mandrel would be a substantial gain in exhaust flow.

[ArunSenior04]

so i actually gained like .5" in pipe?

[evan938]

no, press bent does not mean crush bent. crush bent is the most restrictive bend. it means exactly how it sounds. mandrel bent keeps the exhaust size the same throughout the whole exhuast. press bent is right inbetween those two. its not AS restrictive as crush, but wont flow as well as mandrel

reece- if you got 2.25" crush bent, youre probably only flowing about 2" worth at the bends. also keep in mind when it goes thru the bends its going to sort of clog up the gasses from where youve got 2.25" worth of exhaust trying to go through 2" worth of tube. also the ripples from the exhaust bends is going to disrupt the flow of the exhaust

[ArunSenior04]

But even according to that graph, IF the narrowest bend is at 2", Im only 1/8" at the mmost from the optimal pipe size.


reece- if you got 2.25" crush bent, youre probably only flowing about 2" worth at the bends. also keep in mind when it goes thru the bends its going to sort of clog up the gasses from where youve got 2.25" worth of exhaust trying to go through 2" worth of tube. also the ripples from the exhaust bends is going to disrupt the flow of the exhaust

Another issue is that to have a 2.25" worth of exhaust flowing, I would need to have all the exhaust piping done to that length. Since "the exhaust is only as wide as the narrowest point," by keeping any of the original piping (like the 1 7/8" piping above the resonator right?) I would still only be at 1 7/8, even if I had put 2.25 mandrel on there?

If a cat back actually produces a good 8HP by having 2.25 over 2.00" we are literally bickering over a few insignifigant (1-3) hp. Not to mention the other variables like muffler type.

Another variable is that my muffler, Borla XS, is dyno proven to produce better gains than the Dynomax, Magnaflow, and Flowmaster. So again, some more insignifigant performance gains.

In fact, if you want to look at dyno data, Ford saw a 5hp 4tq increase by changing the muffler alone. So if you subtract the 5hp from the overall cat back exhaust, that leaves you with a 3HP upgrade. Since I have 2.25 crushed bent, I prolly only say maybe 1hp of that, while the 2.25 guys may see all 3. 2Hp difference is really insignifigant.

Evan Im not trying to start a "revolution" or something, but Im just saying that 2.25 crushed bent is fine. Are cars arent high hp cars so the difference in doing some of the n/a mods is not that great. You wont see a huge difference between 2.00 and 2.25. Even with the graph you provided from a reliable expert, unlike us, we should only be running 2 1/8 at the most. Unless you're f/i. A bigger pipe than what is optimal, is performance hurting.

[projectx515]

[QUOTE=ArunSenior04]
If a cat back actually produces a good 8HP by having 2.25 over 2.00" we are literally bickering over a few insignifigant (1-3) hp. Not to mention the other variables like muffler type. QUOTE]

i just wanted to say that 1 -3 hp is not an insignificant gain. everything helps in our attempt to make our cars faster.

but to be on topic ..... imo 2.25 in mandral is going to be the best choice for most people b/c the cat back is the first step in the process in a n/a car. the others being headers intakes ect... most headers i belive are around 2.25 inches or bigger and if you bend a 2.25 in crush bend pipe that only allowing 2 inches worth of flow what was the point. when i did mine with the header i had to get 2.5 inch bent to achive a 2.25 flow and i just went back to a stock catback and there is a huge loss

[02xdGLS]

to second projectx515... yes, 1-3 hp is not nearly as much when you are talking about super cars with 610 or 613 hp... but if it's between 133 and 136... i'd say it matters a bit more than you(arunsenior04) are giving credit for.

but all this theoretical talk is just that. theories. we need to do what evan suggested and finally settle it. now, we just need a willing guinea pig to go get 2.0 in exhaust. :D (i know different mufflers can vary the results but as long as it's similar straight-through muffler type.. aka fart cans... the results should be comparable)

[ArunSenior04]

So you went back to the stock muffler, stock resonator, and stock 1 7/8" piping? Why?

[evan938]

his other stuff was WAY TOO LOUD lol

[ArunSenior04]

to second projectx515... yes, 1-3 hp is not nearly as much when you are talking about super cars with 610 or 613 hp... but if it's between 133 and 136... i'd say it matters a bit more than you(arunsenior04) are giving credit for.

but all this theoretical talk is just that. theories. we just need to do what evan suggested and finally settle it. we just need a willing guinea pig to go get 2.0 in exhaust. :D (i know different muffler can vary the results but as long as it's similar straight-through muffler type.. aka fart cans... the results should be comparable)


LOL I dont mind dynoing my car, but again, there are two many variables. Headers, muffler type (not all the same hp; prolly 1-2hp diff), temp of dyno day, technique (open hood vs. close hood; fans), ft of above sea level, trans type, etc etc

[02xdGLS]

very true. (evan did say he'll take off headers and whatnot to even things out) so we need someone close to evan with all very similar mods but the exhaust... or someone could give evan a 2in exhaust and let him dyno with his ef cat-back and with the 2in exhaust.

or since that's all too much trouble we could just keep on talking about it instead. :D :cool:

[projectx515]

i went back partly b/c of sound but the shop i had do it did it wrong and it was going to cost me to much time and effort and money to fix it right then to just go back to stock and live with the loss until i can do it right... plus having the baby on the way it was way way to loud ..... i got pulled over for it about 1 1/2 after passing a highway patrol officer b/c he could still hear me

[evan938]

auto vs manual.

hell, we could go up to where i dyno'd in PGH if we're just comparing...not going for a high hp number. i will need someones stock airbox assembly, and stock header/flex/2nd cat and someone willing to drive. im out in pittsburgh every month or so, and live in columbus.

[projectx515]

^you can take mine its all in the garage

[evan938]

yeah...thats another option...someone wants to make me a 2" mandrel bent exhaust and get people to pitch in for dyno time ill be the guinea pig...ill go dyno w/ my set up, then switch to the 2" exhaust (i could do it in 30 min in the shop or parking lot) then dyno again. it would be same day, hour apart, same gas, same temp (within a couple degrees) same elevation, etc etc etc

[ArunSenior04]

Damn that sounds loud as hell LOL. The only other exhaust mod I think Ill do it replace the resonator. I dont think I could last a wk with a loud exhaust. I almost got pulled oer last night for what I have LOL.

I do in fact plan to dyno my car. But not til this summer. After I get this exhaust done, im undecuded on what major thing to do next. Perhaps my tc.

[projectx515]

yeah it was the header no cats or resonator into a 2.5 bent catback with a sright through magnaflow ...very loud almost defining inside the car

[ArunSenior04]

LOL damn dude. That sounds horrible.

[ArunSenior04]

Hmm so since, press bent would make the pipe a tad smaller (lets say 1/8 smaller at bends,) than we can safely assume I gained about a 1/4 in in pipe by replacing to 2 1/4 crushed?

[only1db]

this is probably one of the dumbest arguements....

exhaust size should increase atleast a half an inch for N/A...not matter what the original piping size was...

my boys prelude...2.25 stock....almost every exhaust made for it...2.75 same goes for us...2.25 is the best compromise because they dont make piping for a direct .5 inch increase...

look at other modles of vehicles...you will see the same kind of diameter increase...damn where are the physic people...i'm too damn sick to do this one...

[ArunSenior04]

I was only argueing that 2.25 isnt that much greater than 2.00.

[Cypher]

i do have to second derek on this one... this is a stupid pointless argument because you seem set in your ways. i don't think 2.25" is enough to kill our power. i know i felt a big change in my car after i put my exhaust on and i'm happy with it.

oh and i also wanna point out this about your muffler... ford dyno proved that 3 chamber muffler > all. 5whp from one.

[05TidalWave]

I think, from alll my readings/talks, 2.25" FLOW is best - be it 2.5" crush or 2.25 mandrel. The stock 1 7/8 is horrid... Probably limits flow to less than 1.5". I vote Evan on this one.

[ArunSenior04]

ProjectX, did you get a ticket with your exhaust? and if so, how much?

I think, from alll my readings/talks, 2.25" FLOW is best - be it 2.5" crush or 2.25 mandrel. The stock 1 7/8 is horrid... Probably limits flow to less than 1.5". I vote Evan on this one.

Thats what I was thinking. So in upgrading to a 2.25 crushed, I prolly only saw a .5" increase in size. Im not saying that 2.25 is horrible, I was just argueing that crushed 2.25" is a decent (not the best) upgrade over stock. I may not see the 3HP increase of 2.25 mandrel, but I definately wont see 0.

[evan938]

1.875 to 2.250 = .375 (3/8) bigger exhaust piping. not .5 (1/2)

[ArunSenior04]

OOps yea LOL.

[XDGT03]

In order to keep velocity you need to have a decrease in the size of the exhaust pipe down line. Idealy then it probably should start off around 2.5" at the collector or downpipe, and then based upon whether you have a cat or resonator etc... you should gradually decrease to the tailpipe to around the stock size.

This not very practical and would require serious r&d time to figure it all out. I'm not doing and neither is anyone else so...

2.25" crush bent works great

[only1db]

^works...yes...but mendral would be much better...being that hte gas would be able to flow freely through the pipes as opposed to be turbulent beause of the lines in the crush bent

and i swear...if anybody brings up the tornado and says that turbulence are a good thing...i will personally slap them!! LOL!!

[agdaniels]

holy thread revival batman!

How much do you think it would cost for a 2.25" mandrel bent setup?
and would that be sufficient size for a low boost s/c?

[tharptroy]

yeah, a 2.25 setup. Evo Fusion and ARK make 2.25" and 2.5" OD exhausts respectively. evo fusion is cheaper, but you may be waiting for several months. I imagine you'd be looking at $400-800 to have it fabbed

[KeWLKaT]

800$? Nah... Mine probably cost me around 500$ for a mandrel bent 2.5" (though I selected aluminized steel, not SS like most people)

[evan938]

quit reading what you want felix. what he said was $400-$800...

now, i could be completely retarded, but i do believe $500 falls between $400 and $800. then, take into consideration that some places will try to rip you off more than other places...i think what he said was fairly accurate.

[KeWLKaT]

thank you for pointing that out evan, I didnt know 500 was between 400 and 800.

What I meant, sir, was that I don't think such a price should be charged for such a job.

I mean, 400$ of ''difference'' between the cheapest and the most expensive is quite something. I just wanted to make the price window a bit smaller for the guy asking the question.