The most basic exhause question known to man

[HolyShiznit]

I am not gonna read through this thread I will just post up what I know.

3" is NOT too big for the NA KA, it will make MORE power and MORE torque than a smaller exhaust. End story. My N1 duals when I had them NA weren't that loud fairly deep. Any exhaust in reality is gonna be loud, depends on the muffler set ups, resonators (if used), etc.

[ddgsxr504]

A baffle should put you in the ball park of $30-$50 depending on where you get it and what name brand. The best part is you can take it off to hit the track or whatever then put it back on to drive home ect. That way you don't have to worry about the noise ordinance Nazi's!

[Scooby24]

Everyone quit posting up what you THINK is the correct size and someone get some facts in this thread for god's sake.

I want to see back to back dyno graphs of a stock KA w/ stock exhaust versus that same car with a 2.5 inch exhaust.

I also want to see back to back another stock KA w/ stock exhaust versus that same car with a 3 inch exhaust.

HP is not where you sacrifice power. You sacrifice power in the powerband and torque really suffers.

Until I see these things I don't think people should be passing of their own ideas as fact.

[sunnys14]

someone give this guy the link where they dynoed a 5zigen fireball exhaust on the KA and gained 11whp...

[Scooby24]

someone give this guy the link where they dynoed a 5zigen fireball exhaust on the KA and gained 11whp...

I could care less how much power any one given exhaust gives. I want to see powerbands.

That's what wins races...not peak power.

The flatter the torque and hp the better. 11 hp gain from 6000 rpms to 6500 is not going to do a lot of good.

[InsanityInc]

there's been dynos of 2 separate dynos from 3" exhausts. One gained 13whp, one gained 15whp, and didn't lose any power anywhere, and gained quite substantially everywhere in fact.

[Bigvinnie]

HP is not where you sacrifice power. You sacrifice power in the powerband and torque really suffers.

Until I see these things I don't think people should be passing of their own ideas as fact.

Agreed I have the DC sports header, 2.5" exhaust all the way through. I only did this because Rebello Racing specializes in KA's, and does approved dyno testing all day long. They recomend the 2.5", and they build cars that win races. I'd rather listen to a qualified shop than the opinions of most people that can't get there hands on a dynomometer.I want to see some dyno's, not bullshiat from the mind....

[Scooby24]

there's been dynos of 2 separate dynos from 3" exhausts. One gained 13whp, one gained 15whp, and didn't lose any power anywhere, and gained quite substantially everywhere in fact.

Once again. Dynos between two different 3" exhausts is NOT what I'm after here.

I want to see a 2.5 vs. a 3 inch dyno. I want to see the powerband difference. Where the 3 inch may have improved upon the stock everywhere I want to see how much more/less the 2.5 did throughout the powerband.

There is a point where decreasing backpressure more and more will no longer provide substantial gains in peak power but will now cause a loss in power.

Example: My good friend with a 325 AWHP WRX removed his 2.75 inch axleback thinking it was restrictive and hurting his power. He went to the track and was a CONSISTENT 12.4 second car. Removing the axleback caused a noticeable loss in torque down low and no substantial gain in power up top.

Ended up running a 12.6 for a best that visit to the track.

Peak power is unimportant.

[InsanityInc]

Once again. Dynos between two different 3" exhausts is NOT what I'm after here.

I want to see a 2.5 vs. a 3 inch dyno. I want to see the powerband difference. Where the 3 inch may have improved upon the stock everywhere I want to see how much more/less the 2.5 did throughout the powerband.

Nobody has done a 2.5in dyno to my knowledge.

Quote »There is a point where decreasing backpressure more and more will no longer provide substantial gains in peak power but will now cause a loss in power.[/quote]Hey, good job proving you know d!ck about why exhaust systems of differing diameters make different amounts of power. Losing backpressure can never make you lose power. Backpressure is never good. What IS good, however, is exhaust velocity. Reason being that improved exhaust velocity, in addition to low backpressure, significantly helps exhaust scavenging, and cylinder filling during the cam overlap period. Now, due to the bernoulli effect, as the velocity of your exhaust stream increases, the pressure across your exhaust system decreases, which can actually create negative pressure in your exhaust pipe. This is why a properly sized pipe is important. If you run an open header you're going to have 0 backpressure undoubtedly, but your velocity also isn't going to be very high. So you'll get maximal gains from having no backpressure, but will never gain extra from good velocity. While a 2.5" system will gain you more with respect to velocity at lower RPM, it will also cause a restriction as your exhaust CFM increases, and will begin to CAUSE backpressure. A 3" system might lose 2 or 3 whp compare to a 2.5" system in the 3000-4000 range, and they'll be about equal from 4000-5000 but in the 5000+ range, it's going to be considerably better than the 2.5" system, because not only is it not creating backpressure unlike the 2.5", but you are also gaining good velocity at that CFM.

Quote »Example: My good friend with a 325 AWHP WRX removed his 2.75 inch axleback thinking it was restrictive and hurting his power. He went to the track and was a CONSISTENT 12.4 second car. Removing the axleback caused a noticeable loss in torque down low and no substantial gain in power up top.

Ended up running a 12.6 for a best that visit to the track.[/quote]For one, unless you can provide temperature and humidity differentials for the two different days, that's completely meaningless. For another, see above for why that could cause a power loss.

[Scooby24]

Nobody has done a 2.5in dyno to my knowledge.

So how is everyone saying the 3" is better?

Hey, good job proving you know d!ck about why exhaust systems of differing diameters make different amounts of power. Losing backpressure can never make you lose power. Backpressure is never good. What IS good, however, is exhaust velocity. Reason being that improved exhaust velocity, in addition to low backpressure, significantly helps exhaust scavenging, and cylinder filling during the cam overlap period. Now, due to the bernoulli effect, as the velocity of your exhaust stream increases, the pressure across your exhaust system decreases, which can actually create negative pressure in your exhaust pipe. This is why a properly sized pipe is important. If you run an open header you're going to have 0 backpressure undoubtedly, but your velocity also isn't going to be very high. So you'll get maximal gains from having no backpressure, but will never gain extra from good velocity. While a 2.5" system will gain you more with respect to velocity at lower RPM, it will also cause a restriction as your exhaust CFM increases, and will begin to CAUSE backpressure. A 3" system might lose 2 or 3 whp compare to a 2.5" system in the 3000-4000 range, and they'll be about equal from 4000-5000 but in the 5000+ range, it's going to be considerably better than the 2.5" system, because not only is it not creating backpressure unlike the 2.5", but you are also gaining good velocity at that CFM.

Settle down there hotshot. I've been in the world of aftermarket for quite a few years and learned a few things along the way including everything you just stated. I worded it wrong and said it lost power when I meant to say torque. Read through the rest of my wording and you'll see I know it doesn't lose peak power.

For one, unless you can provide temperature and humidity differentials for the two different days, that's completely meaningless. For another, see above for why that could cause a power loss.

He and I both had methanol injection on our vehicles which pretty much cancels out a humidity/temperature issue as the methanol/water mixture completely saturated the intake anyways and evaporation pulled out heat.

But if you'd like a little more evidence I ran 12.6's the time before when he ran 12.4s. When we went out again he ran 12.6's and I still was running 12.6s with no changes to either one of us other than the axel back.

Oh yeah and we're both sponsored autocross racers by a shop with a mustang AWD dyno and he called me to let me know we were right about it losing torque when he went up to dyno it. The powerband was much worse with less packpressure. His peak power was actually a bit higher IIRC but his times were slower and he complained the whole way to the track about how the car felt slower right after taking it off.

I'll see if he has dyno graphs to prove it.

[Bigvinnie]

WOW both of you stop argueing. Secondly Back Pressure is a myth the correct term is called "scavaging". By any means the truth is that scavaging is vitally important to torque numbers. Torque is derived by the by products that the engine and it's bolt ons apply. Technically the scavaging numbers will be placed properlly into a 2.5" pipe rather than a 3" pipe. The reason is the exhaust deals with 2 forms of pulses. One being sound pulses while the other is actually exhaust pulses. The whole concept is to get the 2 pulses in sync in order to provide and even distribution of negative to postive pulses.A 3" pipe will scatter sound pulses making the exhaust pulses actually to slow down in the pipe. Technically you get stagnant NOX gases that sit into a 3" pipe rather than being expelled through the muffler. Hence that provides lower torque numbers due to the fact that the gasses sit in the pipe, rather than using positive pulses to create your torque variable through scavaging.Through a 2.5" pipe sound pulses travel faster, also increasing positive pulses to do there job with scavaging, promoting healthier torque numbers.So while you use 3" pipe to privide high HP out put it minimizes torque. While using a slightly smaller diameter can still make the same HP output numbers and provide a strong torque band. 2.5" pipe is much more fluid to allowing sound pulses to exit faster than a 3" pipe. That also explains why decible numbers on 3" pipe is louder, the pulses slow down, rather than exiting sooner.

[Scooby24]

WOW both of you stop argueing. Secondly Back Pressure is a myth the correct term is called "scavaging". By any means the truth is that scavaging is vitally important to torque numbers. Torque is derived by the by products that the engine and it's bolt ons apply. Technically the scavaging numbers will be placed properlly into a 2.5" pipe rather than a 3" pipe. The reason is the exhaust deals with 2 forms of pulses. One being sound pulses while the other is actually exhaust pulses. The whole concept is to get the 2 pulses in sync in order to provide and even distribution of negative to postive pulses.A 3" pipe will scatter sound pulses making the exhaust pulses actually to slow down in the pipe. Technically you get stagnant NOX gases that sit into a 3" pipe rather than being expelled through the muffler. Hence that provides lower torque numbers due to the fact that the gasses sit in the pipe, rather than using positive pulses to create your torque variable through scavaging.Through a 2.5" pipe sound pulses travel faster, also increasing positive pulses to do there job with scavaging, promoting healthier torque numbers.So while you use 3" pipe to privide high HP out put it minimizes torque. While using a slightly smaller diameter can still make the same HP output numbers and provide a strong torque band. 2.5" pipe is much more fluid to allowing sound pulses to exit faster than a 3" pipe. That also explains why decible numbers on 3" pipe is louder, the pulses slow down, rather than exiting sooner.

Exactly what I was trying to get across. Thanks

[JimmyMethod]

Please God/Mod, lock this thread...Seriously, how many 2.5 is better, 3.0 is better threads does one forum need?

[InsanityInc]

So how is everyone saying the 3" is better?

Because people who have put 2.5" systems on their cars and then put 3" systems (usually to upgrade before turboing it) have gotten better results with the 3" in drag times, feel, etc.

Quote »Settle down there hotshot. I've been in the world of aftermarket for quite a few years and learned a few things along the way including everything you just stated. I worded it wrong and said it lost power when I meant to say torque. Read through the rest of my wording and you'll see I know it doesn't lose peak power. [/quote]Ok, so instead of not only misunderstanding how exhaust flow helps an engine, you also don't understand the relationship between power and torque. Losing backpressure doesn't make you lose power or torque. Horsepower at any given RPM is equal to your torque*rpm/5252. If you lose torque anywhere, you lose power there, too. Backpressure is NEVER GOOD. EVER. Taking away backpressure is ALWAYS good and will NEVER make you lose torque or power anywhere in the powerband.

Quote »He and I both had methanol injection on our vehicles which pretty much cancels out a humidity/temperature issue as the methanol/water mixture completely saturated the intake anyways and evaporation pulled out heat.

But if you'd like a little more evidence I ran 12.6's the time before when he ran 12.4s. When we went out again he ran 12.6's and I still was running 12.6s with no changes to either one of us other than the axel back.[/quote]I already explained why removing it could cause an actual power loss, or were you not listening? He probably reduced backpressure by 1 or 2 psi, but that didn't make up for the velocity he lost. Running a non-full exhaust system is almost never a good idea unless you have an engine of ridiculous displacement.

Quote »Oh yeah and we're both sponsored autocross racers by a shop with a mustang AWD dyno and he called me to let me know we were right about it losing torque when he went up to dyno it. The powerband was much worse with less packpressure. His peak power was actually a bit higher IIRC but his times were slower and he complained the whole way to the track about how the car felt slower right after taking it off.[/quote]ARGH. You don't know ****. Just admit it. Stop blaming backpressure, that's not the problem. I will TRY to explain this once again:

First, you can't lose torque and gain power at a given RPM. Ever. Each cycle of the engine which combusts fuel creates TORQUE. Improved scavenging makes you make more TORQUE. When you combust that mixture more times in a given amount of time, you make more POWER.

Any backpressure will reduce your engine's ability to scavenge properly, as there will be a positive pressure from the exhaust system on your engine's exhaust port. This is NOT good. EVER. For any kind of engine, in any operating condition. It is very obvious that if you're trying to blow something out, you don't want something trying to blow it back in. In fact, the ideal situation is to have something trying to suck something else in.

Now, before I go further, read this, because it's pretty ****ing obvious you have no idea what the bernoulli effect is:

http://en.wikipedia.org/wiki/B...ation

It's very important to what we're talking about, because proper application of it allows you to achieve negative backpressure (suction) in the exhaust. So, what you really want is velocity. This is why slapping a stock restrictive muffler on will never help. You're adding backpressure, but not gaining any velocity. Also, there comes a point at which your pipe simply cannot flow any more CFM, and thus your velocity will never go up once you hit that point, and any more gas you try to stuff through will just create backpressure.

So, in short, you want more velocity and less backpressure, because both of those things will contribute to exhaust scavenging and overlap fill. More backpressure = bad, and less velocity = bad, but your velocity with a larger pipe and muffler will have a much higher cap, so it will be more effective as your engine flows more.

[InsanityInc]

WOW both of you stop argueing. Secondly Back Pressure is a myth the correct term is called "scavaging". By any means the truth is that scavaging is vitally important to torque numbers. Torque is derived by the by products that the engine and it's bolt ons apply. Technically the scavaging numbers will be placed properlly into a 2.5" pipe rather than a 3" pipe. The reason is the exhaust deals with 2 forms of pulses. One being sound pulses while the other is actually exhaust pulses. The whole concept is to get the 2 pulses in sync in order to provide and even distribution of negative to postive pulses.A 3" pipe will scatter sound pulses making the exhaust pulses actually to slow down in the pipe. Technically you get stagnant NOX gases that sit into a 3" pipe rather than being expelled through the muffler. Hence that provides lower torque numbers due to the fact that the gasses sit in the pipe, rather than using positive pulses to create your torque variable through scavaging.Through a 2.5" pipe sound pulses travel faster, also increasing positive pulses to do there job with scavaging, promoting healthier torque numbers.So while you use 3" pipe to privide high HP out put it minimizes torque. While using a slightly smaller diameter can still make the same HP output numbers and provide a strong torque band. 2.5" pipe is much more fluid to allowing sound pulses to exit faster than a 3" pipe. That also explains why decible numbers on 3" pipe is louder, the pulses slow down, rather than exiting sooner.

You can't lose torque and gain power, stop perpetrating this myth.

HORSEPOWER = TORQUE (FT-LBS) * RPM / 5252

It's a calculation based on torque. It is literally impossible by definition to lose torque and gain power. It has nothing to do with sound pulses and everything to do with the ideal gas law and the bernoulli principle. Also, gas is never "sitting" in your exhaust pipe, it always flows out quite quickly, but just more quickly with a smaller pipe, until you hit your CFM wall, at which point the larger pipe will be able to flow more volume.

Also, sound doesn't have any force. When you "feel" a sound, you're feeling the kinetic energy that is producing that sound, not the sound itself. When kinetic energy contacts anything (gases included), it causes that substance to vibrate, producing a certain resonant frequency. Sound isn't a thing, it's just vibrations being carried by matter via kinetic energy, hence why there is no sound in a vacuum, and hence why there is no such thing as "sonic energy".

[Bigvinnie]

You can't lose torque and gain power, stop perpetrating this myth.

Displacement means jack to exhaust size, it has more to do with fuel dumping, stock 270cc injection isn't enough to need 3 inches, if that were the case a high rev SR N/A would need 3 inches as well. That isn't the case at all. I don't perpetrate scavaging, and back pressure are the same thing..Like I've been told numerous times tune your exhaust to the size of your exhaust ports plus 15%, and fuel dump. I am not going to recomend to people to buy a $500 5zigen, or N1 3", if 2.5" can be used at half the cost, I don't see the marketing involved that makes 3" so much better for 1 donkey, and a drop in torque, literally that is all it is.
Modified by Bigvinnie at 8:47 AM 8/31/2005

[Scooby24]

ARGH. You don't know ****. Just admit it. Stop blaming backpressure, that's not the problem. I will TRY to explain this once again:

First, you can't lose torque and gain power at a given RPM. Ever. Each cycle of the engine which combusts fuel creates TORQUE. Improved scavenging makes you make more TORQUE. When you combust that mixture more times in a given amount of time, you make more POWER.

Sorry kiddo you are DEAD wrong. Ever tuned before? Ever sat on a dyno and just played with AFR and timing? Obviously not or you wouldn't be making rediculous statements like this.

I have and I've seen my own car lose torque but gain hp.

In boosted applications it's as simple as adjusting fuel and/or timing.

I adjusted values on my map to make torque more reasonable when I tuned my autocross map as I was finding torque around the corners was too much and the car was getting squirly. My HP curve was virtually unchanged but torque was drastically altered.

Time to rethink your arguement.

[Scooby24]

about 2 seconds of searching found this dynograph.

No changes but just to show you that HP dropped and torque increased from one run to another.

gasp

http://members.cox.net/sohcdriver/Ronni ... %20011.jpg

[Scooby24]

Damn I can't find my dynos of my STi...

Once on the dyno when tuning my baseline torque was 311lbs and 305hp

After tuning it was 353 lbs and 307 hp

care to explain? Boost was left unchanged. AFR and timing was only thing adjusted.

[JimmyMethod]

Seriously Scooby, you can't lose torque and gain HP at the same RPM point. HP is a calculated value from torque. Your PEAK HP can go up and the torque can do the opposite because they normally occur at different points...Learn what HP is, and then we'll talk.

Your engine isn't ALWAYS producing it's peak HP or Torque. Each changes... you really need to learn about basic physics...Sorry for the flame.

[InsanityInc]

Sorry kiddo you are DEAD wrong. Ever tuned before? Ever sat on a dyno and just played with AFR and timing? Obviously not or you wouldn't be making rediculous statements like this.

I have and I've seen my own car lose torque but gain hp.

In boosted applications it's as simple as adjusting fuel and/or timing.

I adjusted values on my map to make torque more reasonable when I tuned my autocross map as I was finding torque around the corners was too much and the car was getting squirly. My HP curve was virtually unchanged but torque was drastically altered.

Time to rethink your arguement.

Time to learn to read, moron.

First, you can't lose torque and gain power at a given RPM. Ever.

Durrr durrr durrrrrr.

[InsanityInc]

Displacement means jack to exhaust size, it has more to do with fuel dumping, stock 270cc injection isn't enough to need 3 inches, if that were the case a high rev SR N/A would need 3 inches as well. That isn't the case at all. I don't perpetrate scavaging, and back pressure are the same thing..

You're right, displacement technically means nothing compared to exhaust size, but 9 times out of 10, more displacement = more exhaust CFM. In the case of FI, you're getting artificial displacement which causes more exhaust CFM. Also, exhaust CFM has absolutely nothing to do with how much fuel you put in. unplug your injectors and crank the engine, you have an exhaust CFM. exhaust CFM has a very rough relationship to power, but depends a LOT on your cams as well. A SR20DE has less CFM potential than a KA24DE, so it needs a smaller pipe. Plus you have to remember that by changing your exhaust diameter/restrictions, you are also increasing the power of your engine, and hence most likely the exhaust CFM. Most other bolt ons will increase that CFM as well. Not to mention that injector size is about the worst way you could possibly gauge anything. I could throw 550cc injectors on my stock KA and change the ECU to work them correctly, and according to you I'd need a larger exhaust.

Quote »Like I've been told numerous times tune your exhaust to the size of your exhaust ports plus 15%, and fuel dump. I am not going to recomend to people to buy a $500 5zigen, or N1 3", if 2.5" can be used at half the cost, I don't see the marketing involved that makes 3" so much better for 1 donkey, and a drop in torque, literally that is all it is.[/quote]So a 2.5" is dyno proven to make above 10whp on a KA? I doubt it. Also, like I already said there is no drop in torque. Plus "half the cost" is a load of ****. It's like 35 bucks more for 2.5" to 3" with BRM. Sure, maybe "half the cost" if you buy some ebay piece of ****.

[DjPantsSpecR]

I just want to help point out, that um, oh god what was it, uh, oh yeah. Insanity just owned yous both.

[ddgsxr504]

I agree with (Jimmy),

Please dear MOD stop this thread before someone gets hurt! 2.5"/3" who gives a $h!t get whatever you want, I am tired of seeing a new thread every week from some NOOB about which one is better. That question is going to be the downfall of this forum! Just get a 3" anyway because 90% of 240SX owners go Boost anyhow wether it be KA/SR/RB whatever. That way you don't have to upgrade later!

TECH SUPPORT! TECH SUPPORT!

[Scooby24]

Seriously Scooby, you can't lose torque and gain HP at the same RPM point. HP is a calculated value from torque. Your PEAK HP can go up and the torque can do the opposite because they normally occur at different points...Learn what HP is, and then we'll talk.

Your engine isn't ALWAYS producing it's peak HP or Torque. Each changes... you really need to learn about basic physics...Sorry for the flame.

There appears to be miscommunication going on because that is not what I'm arguing.

I'm talking about optimal powerband. Optimal torque and horsepower throughout the range. NOT, I repeat NOT hp and torque at a given RPM.

I'd rather have an exhaust on an NA car that will give me the fattest powerband rather than just the highest horsepower.

On an NA KA I believe a 2.5 is what is going to do this and without proper evidence we cannot prove one way or the other which is better but it has been my belief that the 2.5 will be the optimal setup.

As has been stated torque will benefit from better scavaging (thanks Big for the proper term) and if I sacrifice a few ponies up top to have a significantly higher torque curve I would be more than happy to do so. However I've seen no evidence to show a 3" gives more power than a 2.5 so I'm going to go with my hunch that over all the 2.5 is the benefitial size.

There is way too much unnecessary flaming on these boards which leads me to believe the maturity of some of the members here is less than what i'm used to dealing with so I'll adjust my tone for that.

Prove me wrong on the 2.5 being better for NA and I'll change my stance. Until then it's just concepts being thrown around on the intraweb. nothing factual.

[Bigvinnie]

So a 2.5" is dyno proven to make above 10whp on a KA? I doubt it.

No exhaust system by itself will make 10+ HP, a freakin header doesn't even make over 10hp, niether does an intake. This is where all of you misconstrue fact from fiction. Any of those 14WHP dyno's you looked at usually had intake exhaust, or header and exhaust, yada yada yada, the list goes on and on.Enough talk from my end. I could care less and I still smoke most noobs that put a 3" exhaust on there setup, thinkin that there really gettin 14HP.Thats all I give a FU%K about, nothin more nothin less. Buy what you want I don't care, what you put on your engine is your perogitive.

[InsanityInc]

No exhaust system by itself will make 10+ HP, a freakin header doesn't even make over 10hp, niether does an intake. This is where all of you misconstrue fact from fiction. Any of those 14WHP dyno's you looked at usually had intake exhaust, or header and exhaust, yada yada yada, the list goes on and on.Enough talk from my end. I could care less and I still smoke most noobs that put a 3" exhaust on there setup, thinkin that there really gettin 14HP.Thats all I give a FU%K about, nothin more nothin less. Buy what you want I don't care, what you put on your engine is your perogitive.

Uh, no, you're an absolute moron. It's a before and after dyno of the exhaust. An Apex'i N1 made 15whp, and some other turbo size exhaust (wasn't actually 3", I think it was slightly smaller) made 13whp. Just the exhaust.

That's why people say to use a 3".

[Bigvinnie]

Like I said exhaust alone wont pull those numbers.........

[Bigvinnie]

Let me say it again..... By itself it wont pull 10HP...............

[DjPantsSpecR]

thats an entirely bogus rebuttle because you know it was already equiped with that intake before and after the exhaust was bolted on. It a pretty damn good controlled dyno actually.

now you're just nit picking, why would you only want to see what a stock KA can do with a 3 inch? honeslty whoever put on an exhaust and called it a day? "oh this 140 wheel horse is pretty good, i better stop right here"

if you really, really wanted to nit pick, and thats what you are doing, you would be complaining about there not being dyno's of the mods you already have, so you could see the gains your car would get.

also another major point is being missed. Notice rpm for rpm no torque is lost anywhere, even near idle its making more power.

Insanity is still right, and others are just digging themselves deeper, just call it a day