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Discussion Starter #1
ok, well i have almost convinced myself to start with just a d/p and get the catback portion once engine mngmt comes out.
godspeed seems to be having great results this way as well.
i do not want to deal with boost creep or cel's if at all possible.

i understand the "theory" behind divorced vs. bellmouth inlets, but:

are there any potential downsides to a divorced downpipe?
are all bellmouth dp's basically the same? (provided they are the same diameter of course)
has anyone ever noticed an ill effect of the so called turbulence caused by bellmouth openings?
is it beneficial to have the dp coated? (jet-hott for ex)

the only differences i have seen in divorced dp's, aside from diameter of tubing, is the length of separation between the pipes. perrin's seems to be extremely short; while bpm, b&b, vishnu all seem to keep the 2 separate for at least 18" or so.
 

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Any downpipe with a 1-1.5" or so weld extension on the o2 housing will not throw a CEL ( i believe - as we did this on a kid's evo ). so you can get any catless downpipe and probably be ok , if you weld the extension.

As for boost creep... I believe a catback exhaust with a lot of back pressure loss is what does it... not necessarily the DP.

I dont know of any downside to a divorced downpipe other then they usually will cost more (although the perrin DP is cheaper then the GS DP from some stores). The whole idea behind a divorced downpipe is to create less turbulance, so I dont see how it could have any nil side effects, since you're getting all the exhaust out anyways. (whether through a 3" opening or a 4" bell mouth, theres only so much exhaust coming out and Im sure that companies ahve taken that into thought when creating divorced DPs.)

Yes most bellmouths are the same, some have different ways of coming into a 3" hole (some are rapidly squished into a 3" , some gradual, some not gradual), but they all have the same idea... to open up the wastegate side of the turbo.

I dont know about nil affects of bellmouths, but yes they are supposed to be more turbulent... so maybe you lose 2hp or so *shrug*?

Usually just wrapping will be fine, but yes Im sure it'd help to jethott your downpipe as it'd drop engine bay temperatures and help the exhaust flow faster (hotter) - from what I've heard.

As for the difference in the divorced and why some people put the seperation short and some long, i have no clue... I dont see the difference in putting it short or long, as you can either fit it in sooner or later... eitehr way it should be just the same. Perrin seems to be shooting 0 turbulence, so I suppose I'd go with that...

Although I will say I dont understand the point of divorcing the DP if you're not seperating it. Some companies have it to where its just 2 holes in the downpipe instead of one... and I dont see how that helps (as obviously the exhaust isnt just going to jump in the right hole and the wastegate exhaust is going to jump in the left one). So I believe a big key is to have it seperated (perrin's, APS's, etc)... Otherwise you're just sticking a wall in the middle of the exhaust's path or at least I believe so.

Robert~

As for the difference in the downpipes for a CEL free catless system:
 

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Discussion Starter #3
ok, what does JDM stand for??

the staticx hotline strikes again :D
thanks for your input.
anyone else with moderate expertise in this area?
 

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i have had good success with the bosal downpipe--in my 02 wrx and now my sti--i used a check engine light fix--and i have no boost creep-i kept my last cat to increase spool-up
dave/mspt
 

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M.S.P.T said:
i have had good success with the bosal downpipe--in my 02 wrx and now my sti--i used a check engine light fix--and i have no boost creep-i kept my last cat to increase spool-up
dave/mspt
? wouldnt leaving your cat in hurt spool up (hence why everyone makes a catless TBE system and downpipes?) as it is just causing back pressure/blocking exhaust gasses.

Robert~
 

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I love the TurboXS downpipe. I have the TurboXS TBE with a high flow cat and the "TurboXS" Magnaflow. It is quiet and it is fast. A little too fast. F'ing sneaky laser cops!
 

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Hummer said:
I love the TurboXS downpipe. I have the TurboXS TBE with a high flow cat and the "TurboXS" Magnaflow. It is quiet and it is fast. A little too fast. F'ing sneaky laser cops!
hehe having 50+ mods wouldnt help to increase the fastness either would it :)? Man I really love your car, I hope to be close to your mods soon one day. very nice stuff and all very high quality :thumbsupsmiley:

Robert~
 

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new rotors

with a stock turbo car with no management .and the downpipe missing, will spool-up faster then a car with no cats at all.but the car with no cats will have more power at top end .complete loss of back pressure will hurt spoll up.some restriction is needed.drive a car with the downpipe missing and then drive one with no cats.
dave/mspt
 

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well yes, but thats why it is suggested to use a downpipe with the stock catback... plenty of backpressure adn then top end to boot. I dont see how you could possibly run without any exhaust (if thats what you meant) as exhaust would just leak into the engine bay and engine compartment... that and it'd melt everything in sight.

Robert~
 

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Hummer said:
I love the TurboXS downpipe. I have the TurboXS TBE with a high flow cat and the "TurboXS" Magnaflow. It is quiet and it is fast. A little too fast. F'ing sneaky laser cops!
I read some time ago in this forum (if my memory serves me well) that the STi already comes with high flow cats and a downpipe with high flow cats would improve the overall performance little if at all. What's your take on this, Hummer?

I was thinking about getting a cat-free downpipe, but from following StaticX's comments re: downpipe in other threads, I understand that both cats are in the downpipe. Therefore, replacing the stock downpipe with a cat-free after market downpipe results in a cat-free exhaust system, overall. Now I am thinking a high-flow cat downpipe.

As much as I want my car performance to go up, I'd feel terribily guilty to not run necessary environment-care measures in my car... :cry:

-Rich
 

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well another reason there is performance, is because of the fact that the piping is increased. A 3" high flow cat will flow more then the stock high flow cat as it is bigger. So the piping has a lot to do with it as well. Hummer said that his car is "stupid fast" hehe so Im sure a high flow cat wont hurt anything much ;). Just dont worry about it Im sure we're talking about a difference of like 2-3 hp or so... I'll let him respond to your question though, but Im sure its not a big deal.

Robert~
 

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STi or S4 Help!!

I also would be interested in a downpipe with high-flow cats. BOTH of them. There's got to be more than just a few people in here who want to stay legal...
 

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The only problem with that (and the reason no one does it) is the cost. It'll cost you anywhere from 100-150$+ to add a cat... add 2 and you can see it'll be like a ~$500-600 downpipe. Even if you went cat in downpipe and cat in midpipe it'd still be very expensive :(.. If you're willing to pay you could just buy a downpipe, cut out a section and add your cats (not stock, but 3" aftermarket ones obviously).

Robert~
 

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rjhang said:
I read some time ago in this forum (if my memory serves me well) that the STi already comes with high flow cats and a downpipe with high flow cats would improve the overall performance little if at all. What's your take on this, Hummer?

I was thinking about getting a cat-free downpipe, but from following StaticX's comments re: downpipe in other threads, I understand that both cats are in the downpipe. Therefore, replacing the stock downpipe with a cat-free after market downpipe results in a cat-free exhaust system, overall. Now I am thinking a high-flow cat downpipe.

As much as I want my car performance to go up, I'd feel terribily guilty to not run necessary environment-care measures in my car... :cry:

-Rich
The factory exhaust is restrictive. The factory opening in the downpipe is about 2 1/4" {if memory serves}. The TurboXS is a 4" bellmouth. I can HEAR the air rushing down the down pipe. The 2 factory cats and muffler are also restrictive. I read a thread on NASIOC a few months ago about someone who took a 2004 STi exhaust and put it on a modded WRX. The WRX ran poorly and threw CEL.

I am running one high flow cat with zero problems.

Hope that helps.
 

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I took the downpipe off to see what the car would do without any exhaust on it at all, and besides sounding like a mad race car, I didn't notice a huge jump in power. Any reasons why? I thought maybe the ECU was having trouble figuring out what was going on. Anyway, I am contemplating buying the godspeed downpipe. Does anyone with it have a dyno chart of before and after? I just wanted to see the results. I hope that they would be better than what I felt when I took the downpipe off.
 

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I'm in the same boat, I got perrin catless up and downpipes in my wrx, when I get the STi in the spring, I kinda want to keep the downpipe legal (catted) because here in dayton the tree huggers make you do an echeck every time you register your vehicle.

Anyone have any dyno specs on a performance catted downpipe?

Also, do you guys know if my perrin stuff will fit on the sti?
 
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