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Old 02-22-2002, 04:07 AM   #1
Silver_SportTrac
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Question Turbo-back exhaust...how does it work?

hey everyone,
i'm new to turbo-charged cars, well new to cars period, and i'm wondering...how does a turbo-back exhaust help a turbo charged car? I've read that turbo-backs help out the turbo, but i just don't know how. If you can give me a quick turbo 101 lecture i'd appreciate it....also since i'll get a WRX soon, i'd need to know if it's really worth paying almost $1200 for an exhaust when i could get a $500 cat-back system.
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Old 02-22-2002, 04:17 AM   #2
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Back pressure and turbos aren't best friends. Getting rid of cats will lower back pressure, as will increasing the tubing size of the exhaust. Anywhere from 2.5-3" I.D. is a good sized exhaust for these cars. A lot of turbo-back systems replace cats with a high flow cat or remove them all together, cat-backs typically don't alter catalytic convertors. Therefore you will see fewer gains from a cat-back system.
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Old 02-22-2002, 04:22 AM   #3
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Also, I forgot to mention that cat-backs are legal replacements for exhaust components, turbo backs that eliminate cats are "illegal for road use".
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Old 02-22-2002, 02:43 PM   #4
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Originally posted by supermarkus
Also, I forgot to mention that cat-backs are legal replacements for exhaust components, turbo backs that eliminate cats are "illegal for road use".
wait a second. How do i get a legal turbo-back exhaust?? Or by what you said do you mean i have to leave at least one cat on the WRX? Is it only illegal if you take off all the cats and replace it with the turbo-back, or is a turbo-back exhaust illegal period? I've seen a few ppl here with turbo-backs but don't know if they race them exclusively....damnit i'm confused now...and that site was helpful by the way..thanks!
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Old 02-22-2002, 03:38 PM   #5
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Quote:
wait a second. How do i get a legal turbo-back exhaust?? Or by what you said do you mean i have to leave at least one cat on the WRX? Is it only illegal if you take off all the cats and replace it with the turbo-back, or is a turbo-back exhaust illegal period? I've seen a few ppl here with turbo-backs but don't know if they race them exclusively....damnit i'm confused now...and that site was helpful by the way..thanks!
Well....you don't get a legal turbo back exhaust. If you alter your cats at all you are doing something illegal in theory. You can only replace a cat if it is not functioning properly. And even then, you are supposed to replace it with a unit that functions in the same way. The people you see with turbo back exhaust systems are doing something illegal, but they are cool with that.

Dave
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Old 02-23-2002, 04:40 PM   #6
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ok...so how much HP would i gain with a complete turbo back exhaust? I looked on subaruwrxparts.com and saw the BPM GT exhaust turbo-back system for under $1K...but is this one legal?

i searched this site and found that the WRX has only 2 cats, not 3. Turns out the third one is just a resonater...so would i be doing anything illegal if i just took off one cat and replaced it with a high-flow uppipe? I've read that people bought a borla exhaust and just added a stromug uppipe to make it perform even better...but does it perform as well as a true turbo-back system? Also, i'd still have one cat left, so it can't really be illegal....by the way how the hell do cops know that your car is illegal anyways?! does taking off all the cat's make a very distinctive sound that yells out NO CATS ON THIS CAR?!?

Damnit...i don't even have my WRX yet and already i'm stressing about what exhaust to get for max pefromance...THAT WILL STILL BE LEGAL!! Also, i'm getting a slushbox, and not all the aftermarket exhausts fit the AT WRX's....so any suggestions for a high performance exhaust(thats legal) would be greatly appreciated!
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Old 02-24-2002, 02:32 AM   #7
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well, while we're on the subject..

I just bought my WRX yesterday and I want to do turbo-back exhaust.

will this hurt the cars daily driveability?

I dont really see how it could but I want to make sure.
also, which brand turbo-back yeilds the most power gain, and how much is that gain HP-wise?
What about warranty issues? will it void it?

Thanks, I'm a total n00b to this stuff, still learning about the car

-Justin
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Old 02-24-2002, 05:02 AM   #8
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Quote:
Originally posted by Silver_SportTrac
i searched this site and found that the WRX has only 2 cats, not 3. Turns out the third one is just a resonater...
Wrong, there are 3 cats on the car. Up-pipe, down pipe, and mid pip. Do more research, the answers are out there and other people have answered this question a million times better than I can hope to. Let me reiterate, altering a functioning cat is illegal under federal law, this includes removing cats and replacing them with high flow cats. Removing the cats reduces back pressure, some manufacturers claim upwards of 20 hp from going to a 3" turbo-back with no cats.
The only thing that will void your warranty is racing the car or taking out of the country. That's it. SOA can choose to not do work under warranty if they determine an aftermarket part caused damages somewhere, but they can't say things like your wheels caused your radio to die. They have to prove a direct correlation between the part and the problem. Good luck trying to get them to believe that though, lots of people argue this fact with their service managers, some are starting to lose that argument.
You guys have to remember that the aftermarket arena for WRXs is relatively small and untested here. People are working on creating safe, reliable aftermarket goods for the USDM WRX but even so, time will tell us what works and what is snake oil or harmful.
I say wait a while and learn how to drive your cars in the stock form, get really in tune with it, and then start experimenting with aftermarket parts. These cars behave differently than 2wd cars and lots of people jumping on the Subaru bandwagon have never driven a 4wd car in their lives. There is a slight learning curve to driving these cars, especially one with as much juice as a WRX. Take lots of time to learn your car. Plus, if you take your time, you'll get to learn what actually works for the car. Let other people do the R&D for you, otherwise there is no getting around the addage "You play, you pay".
The BPM GT should say somewhere on the site that it's for offroad use only since it deletes the downpipe cat, it brings a mid pipe high flow cat to the party though.
Also, the consensus is that the little tiny turbo in this car and a slush box don't go together so well. Unless you plan more major upgrades to the car (torque convertor for starters) 4EAT will not bring you stunning performance. Manual is the way to go for performance driving, 4EAT is great for commuter cars and hilly areas. Sad but true.
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