The Truth about Exhaust

[napkinthief]

This is out to all of you who are running an aftermarket exhaust, compared to a stock exhaust. How much power are you actually gaining for having a 2.5 or a 3" FULL exhaust, from the turbo back. I cant see how just having a free flowing exhaust can add a decent amount of horsepower for the amount of noise it makes. Decent I mean around 10 plus hp. I am going turbo very soon, just need a manifold and ic piping, and I dont really want to upgrade my exhaust. I have a 2.5" muffler and it is annoying as hell. I want to do dual exhaust down to 1.5" pipes after the cat and stick in as many resonators as possible just to get the noise as low as possible. What kind of hp loss and I going to feel for doing this?

 

[JDNSBR]

This is out to all of you who are running an aftermarket exhaust, compared to a stock exhaust. How much power are you actually gaining for having a 2.5 or a 3" FULL exhaust, from the turbo back. I cant see how just having a free flowing exhaust can add a decent amount of horsepower for the amount of noise it makes. Decent I mean around 10 plus hp. I am going turbo very soon, just need a manifold and ic piping, and I dont really want to upgrade my exhaust. I have a 2.5" muffler and it is annoying as hell. I want to do dual exhaust down to 1.5" pipes after the cat and stick in as many resonators as possible just to get the noise as low as possible. What kind of hp loss and I going to feel for doing this?

Compared to a free flowing exhaust? Quite a bit. Turbo cars need fuel and air to function correctly. To do an upgrade you want to have the most free flowing pipes to allow the air to flow quickly. Hence the reason for bigger intercooler piping. The thought process is the same for the exhaust. The exhaust will get rid of the fumes the engine produces when the gasoline combusts. The more effeciently you get rid of this the more your engine can flow. When you start putting in bends, resonators, cats, ect you start to back up this system. Yes, it will be quieter but you are choking the engine of HP. If power gains are your goal this is just something to think about.

 

[kottyking]

Also if its sound youre worried about, my friends n/a w/ a fart can was louder then my exhaust.

 

[larsrya8]

The turbo itself helps dull the sound, which is why a turbo car with a large exhaust isn't nearly as raspy as a N/A car would be. They usually end up only being excessively loud at WOT, which you shouldn't be doing if you're worried about noise anyway.

 

[Justfat]

This is out to all of you who are running an aftermarket exhaust, compared to a stock exhaust. How much power are you actually gaining for having a 2.5 or a 3" FULL exhaust, from the turbo back. I cant see how just having a free flowing exhaust can add a decent amount of horsepower for the amount of noise it makes. Decent I mean around 10 plus hp. I am going turbo very soon, just need a manifold and ic piping, and I dont really want to upgrade my exhaust. I have a 2.5" muffler and it is annoying as hell. I want to do dual exhaust down to 1.5" pipes after the cat and stick in as many resonators as possible just to get the noise as low as possible. What kind of hp loss and I going to feel for doing this?

the added noise is a bummer, but your car NEEDS to breathe, just think all that extra upgrades for more air to be thrown into the system (manifold, FMIC, Turbo upgrade) where is it all gonna go? why even waste the cash on 1 and not the other. intake and exaust work hand in hand, they benifit each other greatly. but it sounds like you are like me and dont want that louuuuud raspy obnoxious sound of a big exaust. look into spending the extra cash on a very good exaust system. for applications less than 350 HP go with the 2.5 inch.

 

[underradar92]

Adding a turbo to your current setup will quiet it down quite a bit, but I feel your pain. My setup is still just a bit to noisy for me, (see profile) but I'm old. I am going to add 1 more 3" dynomax race magnum so I can get away with even more evil driving.

 

[staticbrainwash]

try this, 2.5" into 3" dp (as most dp's are). but get one that isn't cat elim. that way you can put in a high flow cat which will quiet your system quite a bit, then, put in one resonator and an oval can straight through muffler. all 3".

I am one of 3 turbo dsm's in my city with exhaust. other than that there's my buddy with a TT stealth and a friend of his with a 500hp turbo mercedes. Everything else is a neon or sunfire or cavalier or civic all riced out with wings and fart cans. i can drive around and not get many turned heads, but as soon as those fart cans buzz by everyone is looking and laughing. (ive got basically a 3" straight pipe with a small walled bullet muffler). my exhaust may be loud, but it's deep toned and mean, espically at WOT.

Maybe that helps a little bit with some examples. But i would try a cat, those tend to quiet things a lot without sacrificing too much power and flow. Otherwise i agree with everyone else, if you're looking for more power from a turbo, why skimp on the system and keep the tiny 2.25" stock pressbent exhaust?

 

[daren_p]

Actually you will see nice gains going say 3" over the punny factory exhaust. Turbo cars aren't like NA cars when it comes to exhaust upgrades you will actually see some real gains, in both hp/torque but will also spool the turbo faster. Like has been said turbo cars are also alot quiter then NA as well. I run a 3" downpipe, 3" high flow cat to an Apexi N1 catback (which is also 3" +) and when I did I dB test I measured 83 dB (without the silencer). To compare my old man corvette with factory exhaust read 90 dB testing the exact same way.

 

[my98GST]

Just out of curiousity... What is stock piping on the GST/X?

For those who are curious also, Is there a big difference from the stock to a 2.5" exhaust? Then is there a big difference between the 2.5"-3"?

 

[daren_p]

Just out of curiousity... What is stock piping on the GST/X?

For those who are curious also, Is there a big difference from the stock to a 2.5" exhaust? Then is there a big difference between the 2.5"-3"?

The diameter of the stock exhaust varies but I believe it necks down to 1.75" in some of the sections like the flex etc. When you go from 2.5" to 3" it doesn't seem like its that much bigger, because it only it's only .5" but if you actually work out the difference in area you see why .5" flows alot more

Stock 1.75, area = 2.4"
2.5" exhaust, area = 4.9"
3" exhaust, area = 7.1"

 

[xveganxcowboyx]

The best way to think about exhaust is as a power magnifier. JUST changing the exhaust will not net you huge gains from a stock (or in your case) low boost application. As you p the boost and start trying to make real power, you will notice a big difference one way or another.

I'm just going to make these numbers up to illustrate my point, but this is how it would work:

A stock turbo engine with stock exhaust makes 200 horses.

A stock turbo engine with 3" exhaust makes 210 horses.

A turbo engine with 18 lbs of boost on stock exhaust makes 240 horses.

A turbo engine with 18 lbs of boost and 3' exhaust makes 270 horses.

It will allow you to make much more power with the same modifications. it's considered one of the 'essentials' to making power. As people always say, your engine has got to be able to breath properly before it can make good power.

 

[JessesTalon]

Fact: I had a stock 94 eagle talon tsi awd..

Fact: I ran at the track bone stock 15.1

Fact: I added 3" pressbent exhaust no cat 3" straight through magnaflow muffler costing me 300$ Boost @ 15psi

Fact: I ran at the track 13.5 @ 98.8...


so your telling me I only gained 10hp? I don't think so.

The best way to think about exhaust is as a power magnifier. JUST changing the exhaust will not net you huge gains from a stock (or in your case) low boost application. As you p the boost and start trying to make real power, you will notice a big difference one way or another.

I'm just going to make these numbers up to illustrate my point, but this is how it would work:

A stock turbo engine with stock exhaust makes 200 horses.

A stock turbo engine with 3" exhaust makes 210 horses.

A turbo engine with 18 lbs of boost on stock exhaust makes 240 horses.

A turbo engine with 18 lbs of boost and 3' exhaust makes 270 horses.

It will allow you to make much more power with the same modifications. it's considered one of the 'essentials' to making power. As people always say, your engine has got to be able to breath properly before it can make good power.

 

[Ultimatedsm]

You don't see a huge gain if you are stock. If you slap on a 20G TDO6 with the stock exhaust you will loose around 40 HP because of the exhaust restriction. Exhaust systems start helping when you start to push more air into the engine. If your pushing in 12 psi at 325 CFm, then your going to push out the after math of that through the combustion process, if your pushing 18 psi at 600 CFM, your going to push the after math of that. With the stock exhaust, the 12 psi at 325CFM it isn't too bad, its not a huge restriction at that point. However, at 18 psi flowing 600CFM, that stock exhaust is like a straw. Try blowing through a straw then something 4 times as large same concept.

 

[alcali247]

This is out to all of you who are running an aftermarket exhaust, compared to a stock exhaust. How much power are you actually gaining for having a 2.5 or a 3" FULL exhaust, from the turbo back. I cant see how just having a free flowing exhaust can add a decent amount of horsepower for the amount of noise it makes. Decent I mean around 10 plus hp. I am going turbo very soon, just need a manifold and ic piping, and I dont really want to upgrade my exhaust. I have a 2.5" muffler and it is annoying as hell. I want to do dual exhaust down to 1.5" pipes after the cat and stick in as many resonators as possible just to get the noise as low as possible. What kind of hp loss and I going to feel for doing this?

are you serious? i can't believe people are even replying to this. If your trying to get the most performance out of a turbo car then the less restriction is better. Thats why people like running open down pipe if they can. Anyway you hava a N/A turbo so who cares what size you use. Even if you get a turbo what are you going to run 8 lbs of boost? If your into performance than get a 3in exhaust if your looking for a quite sound drive your moms car. Sorry for even replying to this.

 

[xveganxcowboyx]

Fact: I had a stock 94 eagle talon tsi awd..

Fact: I ran at the track bone stock 15.1

Fact: I added 3" pressbent exhaust no cat 3" straight through magnaflow muffler costing me 300$ Boost @ 15psi

Fact: I ran at the track 13.5 @ 98.8...


so your telling me I only gained 10hp? I don't think so.

Please, read again. Key quotes:

"I'm just going to make these numbers up to illustrate my point"

"A turbo engine with 18 lbs of boost and 3' exhaust makes 270 horses"

You don't think running 15 lbs of boost had an effect on those numbers?

 

[-red97rum-]

This is out to all of you who are running an aftermarket exhaust, compared to a stock exhaust. How much power are you actually gaining for having a 2.5 or a 3" FULL exhaust, from the turbo back. I cant see how just having a free flowing exhaust can add a decent amount of horsepower for the amount of noise it makes. Decent I mean around 10 plus hp. I am going turbo very soon, just need a manifold and ic piping, and I dont really want to upgrade my exhaust. I have a 2.5" muffler and it is annoying as hell. I want to do dual exhaust down to 1.5" pipes after the cat and stick in as many resonators as possible just to get the noise as low as possible. What kind of hp loss and I going to feel for doing this?

What in this post illustrates the truth about exhaust? If you want to make the most power, you will want a free flowing exhaust, bottom line.

 

[Spoolin4Ever]

Faster spoolup especially with an EVO3 or bigger turbo

 

[91gst]

well im on the same page as the original poster but took a step closer to being the ultimate sleeper. i know many people have done it before. i picked up a stock fwd catback. im gonna run the evo02 housing( i took off my atmospheric dump o2 housing) 3 inch downpipe and a cutout right before the cat. on the streets the cutout will stay closed but on the track ill open it up. i dont know if im gonna have the electric one but i guess i might as well so i won have to keep crawling under the car. on my t3/to4b v-trim turbo with all my stock exhaust in place i just dont push the car i just drive to school anyway. its nice to be able to hear myself think or to listen to the radio on the highway.

 

[Ryan95tsiAWD]

you can buy generic 3" "bullet" style silencers (advanced has them) that will not hurt performance and keeps the car down to a low rumble. I have one after the flex along with a cheap-o dynamax muffler and my car does not bother me at idle or on the highway.
Total for o2 back 3" exhaust, including muffler shop charge to weld and hang everything: $210.00

I think N1 mufflers START at that price!

For those that think a stock car doesnt see gains with exhaust. Try unbolting your downpipe and see how your car feels.

 

[JX6]

well im on the same page as the original poster but took a step closer to being the ultimate sleeper. i know many people have done it before. i picked up a stock fwd catback. im gonna run the evo02 housing( i took off my atmospheric dump o2 housing) 3 inch downpipe and a cutout right before the cat. on the streets the cutout will stay closed but on the track ill open it up. i dont know if im gonna have the electric one but i guess i might as well so i won have to keep crawling under the car. on my t3/to4b v-trim turbo with all my stock exhaust in place i just dont push the car i just drive to school anyway. its nice to be able to hear myself think or to listen to the radio on the highway.

Well I found a soultion for the noise issue. It appears that MY o2 dump only opens when I am hitting my boost limit so all I have to do is go easy on the gas and I have no problems.
When I want to scare people I open it up.

 

[napkinthief]

are you serious? i can't believe people are even replying to this. If your trying to get the most performance out of a turbo car then the less restriction is better. Thats why people like running open down pipe if they can. Anyway you hava a N/A turbo so who cares what size you use. Even if you get a turbo what are you going to run 8 lbs of boost? If your into performance than get a 3in exhaust if your looking for a quite sound drive your moms car. Sorry for even replying to this.

Well obviously, the less restriction the more power. This is easily proven using your hand and a tub of water. Swing your hand through the air then swing it through the water, which one goes faster and has more power? OK.


I want something that is not loud, but does not depreciate my power too much. I have the stock exhaust right now with a straight through muffler, and its annoying the crap outta me. It just sucks that everytime I step on the gas I have to hear BRRRRRRRR. Yes I am into performance, but my car isn't a track or dyno car, and I dont use it to race much, just like a quick car to match my personality. There are a lot of helpful posts here, and yours isn't one of them.

you can buy generic 3" "bullet" style silencers (advanced has them) that will not hurt performance and keeps the car down to a low rumble. I have one after the flex along with a cheap-o dynamax muffler and my car does not bother me at idle or on the highway.
Total for o2 back 3" exhaust, including muffler shop charge to weld and hang everything: $210.00

aren't they just resonators?




and one of my original questions is unanswered, is a dual 1.5" exhaust after the cat the same as a 3" restriction wise, if you factor out the bends?

 

[Dream On]

I don't think so. It has to do with cross sectional area I believe. pi*3^2 = 28.26 in^2 while 2*pi*1.5^2 = 14.13 in^2

 

[Ryan95tsiAWD]

aren't they just resonators?

You got it...couldn't think of the name.

 

[staticbrainwash]

think about something for a sec. take a NA car or any car with a small exhaust pipe and a large tipped straight though muffler. they are LOUD and buzzy and gross. take then a turbo car, with a nice 3" exhaust, high flow cat maybe a resonator and an oval can straight through muffler. still loud, but not as bad by any means. and it sounds cool.

now i know adding a turbo will change exhaust sound a bit, but it also has something to do with pipe diameter. for example, a truck with a v8 that has 1.5"-2" straight pipe duals = LOUD AS HELL! take that same truck put nice sized pipe on it with nice mufflers = totally different sound.

what im saying is, it's all on how you go about the system. personally i'd think that the dual exhaust would make it sound kinda gross, but i've never heard a turbo dsm with duals. i'd just stick with 3"-high flow cat-possible resonator-oval can dual tip muffler. you've got a nice flowing system that isn't loud, just low toned and mean.

 

[coltboostin]

are you serious? i can't believe people are even replying to this. If your trying to get the most performance out of a turbo car then the less restriction is better. Thats why people like running open down pipe if they can. Anyway you hava a N/A turbo so who cares what size you use. Even if you get a turbo what are you going to run 8 lbs of boost? If your into performance than get a 3in exhaust if your looking for a quite sound drive your moms car. Sorry for even replying to this.

I agree with this guy.

Looking at post one, performance is not his real goal. I wont venture a guess at what is, but I can guess it involves a certain noise.