exhaust?

[GTDrifter]

ok im making my own exhaust for a senior project and have some questions

what is the stock size pipes on a bd?

also, what are the secrets for a loud but nice sounding exhaust? i see some tips that have like an inner pipe with holes on the sides so anything important there?

[Sarra]

2.25" is stock. Can't help you with your other questions though. :)

[rougeben83]

2.25" is stock. Can't help you with your other questions though. :)

Ugh no it's not. On an 06+ WRX it is.

[98BG5GT]

If this is senior project, what is your goal? Loud and nasty? Deep and mellow? Ratty....tinny? Performance gains? What is your budget? I would totally go stainless all the way through, 2.25" to 2.5" should do for your BD. Are you also fabricating a resonator and/or muffler? You could go all out and build a 3" catback that splits into two 2.5" pipes under the rear transaxle then back into a 3" muffler. I had a similar HKS system on my MK3 turbo Supra. It was quite a conversation piece! Have fun :wink:

[GTDrifter]

i like it loud but it sounds nice i would like it to sound mellow like low tone

im making it out of carbon fiber and running it maybe from right after the two pipes that come down from the engine to the O2 sensor and then pick it back up after that peice and run it the rest of the way

im also making an short ram air intake

[Huffer]

i like it loud but it sounds nice i would like it to sound mellow like low tone

im making it out of carbon fiber and running it maybe from right after the two pipes that come down from the engine to the O2 sensor and then pick it back up after that peice and run it the rest of the way

im also making an short ram air intake

So you're making a header-back exhaust? you do realize that you have a catalytic converter in there too. A better idea would be to make it a cat-back exhaust. Less to worry about.

You could still be innovative and have the pipe do a Y-split and exit from 2 two-inch mufflers in front of the rear wheels, hot rod style.

[Airgne]

i think that would be bad ass.

[Sarra]

2.25" is stock. Can't help you with your other questions though. :)

Ugh no it's not. On an 06+ WRX it is.

My 2002 WRX has 2.5" piping. 2.5 NA motors came with 2.25" piping. 2.2 and 1.8's came with smaller. The 1996 might have had 2", I'm not very farmiliar with them, but both my BK and BE, and my mom's BH, have 2.25" pipe.

[track8]

Both the OEM aftercats on my previous BJ-L and the current BK-GT, were a bit under 2" OD.

[GTDrifter]

i was thinking of doing that for a while but the whole cutout for the exhaust in the rear bumper/lip and no exhaust being there would bug the crap out of me

[outbacktweaked95]

what about the carbon fiber idea what exactly are you planning on doing with that and a GT BD has 2.25 pipe and 95 BK has 2.0 +- 0.01 inch i used the calipers on it tonight while drawing up my flanges. also for an idea about sonds of cars you might want to look at the sound clips theyll help you with what system sounds like.

[GTDrifter]

im planning on making the entire exhause (pipe and all) from carbon fiber im in CAD so im going to make a 2.25" thick cylinder in the prototype machine to help make it perfect

i want a low mellow sound that sounds nice

[jey]

My 2002 WRX has 2.5" piping.

Is it 2.5" all the way back? I've had a WRX exhaust on my car - it dwindles down to 2" by the time it gets to the muffler. It's disgusting...

[Mikey97D]

im planning on making the entire exhause (pipe and all) from carbon fiber im in CAD so im going to make a 2.25" thick cylinder in the prototype machine to help make it perfect

i want a low mellow sound that sounds nice

How will you mount the exhaust? ie, where the exhaust hangars go. Just a suggestion, use a metal collar around the cf tube for the mount areas. Cf oblongs for bolts holes with vibration (motor). Interesting project. Good luck with it.

[rougeben83]

My 2002 WRX has 2.5" piping.

Is it 2.5" all the way back? I've had a WRX exhaust on my car - it dwindles down to 2" by the time it gets to the muffler. It's disgusting...

Seriously, it isn't. I don't know how he measured it, but they're no where near close to 2.5". That's why borla and other aftermarket exhaust companies initially offered exhausts in 2.5" pipe for the WRX's.

https://sl-i.net/FORUM/images/imported/2008/09/P1060778-1.jpg

06 WRX muffler (a little under 2.25" actually, 55mm), the leftover exhaust pipe welded at the end of it is 2.5", the flange section is from an STi muffler (60mm).

[winston856]

My 2002 WRX has 2.5" piping.

Is it 2.5" all the way back? I've had a WRX exhaust on my car - it dwindles down to 2" by the time it gets to the muffler. It's disgusting...

Maybe for turbo applications but I've heard (for n/a) that having it taper down near the end like that keeps the velocity up for more torque.

Don't know how true that is but it makes sense.

[Sarra]

Last I looked mine was 2.5" at the axle back.

2.25" is 'perfect' for NA, 3" is 'perfect' for most turbo applications.

[GTDrifter]

ok so tapering it from 2.25 to 2" would give me more torque?

ill probably do that near the end or should i taper it somewhere else

does anybody know how to design it to get a low, mellow tone at all?

[Sarra]

Theoretically, a teper should give you more power. As the exhaust gasses cool, they contract.

I know that even after an hour of driving my WRX as hard as I can, the muffler and pipe leading up to it is still cold to the touch. It only heats up if you let it idle for a long time.

[track8]

Theoretically, a teper should give you more power. As the exhaust gasses cool, they contract.Not exactly, cooler gasses don't move as fluidly and you end up with more backpressure, torque peaks at a lower RPM point and horsepower goes down, usually.

[GTDrifter]

ok so should i taper it or not?

also doesnt anybody know why some exhausts have the holes inside of it drilled?
i saw one at wal mart today like on the inside wall of the pipe theres holes going around it

[outbacktweaked95]

about the whole carbon fiber idea it sounds good and all but at school we make airplanes and airfoils out of carbon fiber and there expensive as crap. im pretty sure that it wont handle the heat for long either. ill talk to my professors in the aerodynamics lab tom and check it out for school but u might want to go with making a intake out of carbon fiber instead of the exaust. sounds really neat though. also if you want im just finishing up my exaust and i can give you the drawings of my cat back system on my sation wagon if you wan them there cad files and such as well as a custom flage to adapt the system.

[Mikey97D]

Curiosity, what CAD systems are you using?

[Sarra]

Instead of a taper, I'd suggest heat wrapping the entire exhaust. Keep the heat in the gas until it comes out the exhaust. Or, do a thick ceramic coating, WRC style. Though, the WRX cars tend to have the cat right at the end of the exhaust...

[GTDrifter]

i was sent a letter from an aeronotics school in florida but i chose not to even contact cause the letter said that rich kids get all this stuff handed to them im not poor, im not rich so yeah

i go to vo tech for CAD the school has to have all the latest systems by law so we will have Autodesk Inventor, AutoCAD 2009, and some machining programs and landscaping, etc.

im making both the exhaust and the intake...i could put heat wrap on the inside of the pipe...itll be complicated but i have an idea

i would like the drawings though could you tell me if you had the holes inside or no...ill find a pic after my football game

[Huffer]

i was sent a letter from an aeronotics school in florida but i chose not to even contact cause the letter said that rich kids get all this stuff handed to them im not poor, im not rich so yeah

You kids confuse me. What the heck does this have to do with making an exhaust system?

[liquidracing]

gtdrifter, the stock exhaust is actually 1.75" measured by way of micrometer. if by bd you mean a 1996 legacy GT, LSi, Ls, or L......that being said, tapering down will give you more back pressure, which does not equal more power....however, you can open up the pipe too much and lose power the other way. the best "sounding" n/a exhaust i've seen, or heard, actually is very, very simple...and cheap! it is the ever present cherry bomb glass pak(origional cherry bomb) and a set of borla headers...keeping the entire middle section of your exhaust in tact! want better flow? hi-flow cat. that's it! guaranteed you will net, at minimum, +10hp from headers, and about 1/2-1hp from the unrestrictive glass pak(as long as you make sure the exaust flows over the paks louvers as opposed to in the louvers...yes, cherry bombs can be installed in a louder unrestrictive position, or, flip it around and have a quieter more restricted flow and sound, thus losing the 1/2-1hp gain from the pak. just my 2 cents....the bombs only $20, headers...about $250-300(new). so does 10-15hp increase for under $300 sound like a winning combo? i love mine.....:)

[liquidracing]

oh yeah, btw....hi-flow cats about $200, and you might be lucky to see another 5hp, although i'd believe it to increase realistically by abou 1-2hp...not that i'm into fluid dynamics...que es mi nombre?

[outbacktweaked95]

i was sent a letter from an aeronotics school in florida but i chose not to even contact cause the letter said that rich kids get all this stuff handed to them im not poor, im not rich so yeah

i go to vo tech for CAD the school has to have all the latest systems by law so we will have Autodesk Inventor, AutoCAD 2009, and some machining programs and landscaping, etc.

im making both the exhaust and the intake...i could put heat wrap on the inside of the pipe...itll be complicated but i have an idea

i would like the drawings though could you tell me if you had the holes inside or no...ill find a pic after my football game

not sure what holes your talking about all i did was get a pipe bent for my exaust. also for long term use carbon fiber deteroriates fast with heat and with a heat wrap on the inside it will stil leak through. but just for an idea i work with a guy that is making a carbon fiber pool stick with all kinds of neat stuff to and hes actually awating the patten now but his cost to make the stick butt which is about a 2 ftx 2 in pipe and as well as the rest of the stick was upwards of two grand for it. Also for carbon fiber your suposed to use a type of vaccum chamber to make the stuff all go together right. not super fluent with it but from what i understand its not like fiberglass where you use resin and cloth and it works you are supposed to have some type of a pressure thing. not super sure of the process.

[outbacktweaked95]

here are some prices about carbon fiber you might want to take a look at
http://www.aircraftspruce.com/menus/cm/carbonfiber.html

http://www.mazda3forums.com/index.php?topic=69741

[GTDrifter]

i know a company that makes it

there are different types of carbon fiber too...also different weaves

its hard to describe the holes like if you look on a machine gun, sometimes they have that heat shield...the tube of metal with holes drilled though it to dissapate the heat ill look for a pic quick

http://www.freefoto.com/images/22/01/22 ... un_web.jpg (http://www.freefoto.com/images/22/01/22_01_4---U-S--Army-Machine-Gun_web.jpg)

its like that but its on the inside

[GTDrifter]

oh also i have a bd its a 1998 GT

[outbacktweaked95]

Alright I finally got around to talking to a guy about carbon fiber and he has done monling and such. He told me that you have to in some way vaccume it no way around it and that it will got to 600 degrees F plus or minus some. also i get what your talking about with the holes idea but i dont inderstand where do you want to put it. inside to muffeler? Also if I were you i would start out with the intake and see how that all goes and then go to the exaust. Also if your still interested in this idea th guy told me about a way to make the molding with what he called a lost wax mold whick means you make the part out of machiniable wax then do the carbon stuff and then heat it up the wax will just melt out leaving a purfect mold. thats about all the info that i have besides its going to be an expensive project id say for the exaust look in the thousands range before its all done. thinking about it it cant be to aweful much better than aluminum becaue thats what F1 cars use and money is no problem to them.

[GTDrifter]

yeah...i probably cant do this then i dont have a vaccuum chamber but i could probably make one but getting it to 600 degrees inside a school is sorta a bad idea

thats the only obstacle in my way...i think im just guna make it from alluminum or something

as for those holes i always see them inside the tip all the way at the end right before the gasses come out...if i can find a pic then ill post it

[track8]

ok so should i taper it or not?

also doesnt anybody know why some exhausts have the holes inside of it drilled?
i saw one at wal mart today like on the inside wall of the pipe theres holes going around itIt's an absorptive baffle style muffler, otherwise known as a glasspack.

[GTDrifter]

ok thanks for saying what that was now i know

but does anybody know how to get a low/mellow tone that sounds good just by redoing the exhaust?

[track8]

Exhaust sound tuning is a black art, luck, trial and error and more importantly, entirely subjective. The most sure fire way is to hear live (not sound clips) cars running and try to duplicate the headers and baffling types being used.

My Legacy, as one example, currently sounds nothing like a Subaru. It sounds a lot like a turbo DSM, (a happy coincidence) minus the cool turbo noises. It no longer displays the "Subaru Burble" as I prefer to call it, but it is lower frequency than a N/A 1.6 or 1.8 litre inline 4. It is a bit raspy at the moment but, I'm planning to add a metal substrate cat soon.

Hardly a definitive answer I know, but likely the most realistic.

[jg09]

but getting it to 600 degrees inside a school is sorta a bad idea

This is true, but what about buying an old oven, taking out the racks, and doing it outside of school?

[GTDrifter]

it sounds to me like you need to heat it while vaccuuming it