turboxs 4" downpipe?? - Subaru WRX Forum
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#1 Old 12-01-2008, 11:19 PM
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turboxs 4" downpipe??

isn't that too much?? a 4 inch downpipe?? i mean i know most downpipes are about 3 inches but u would think if it's 4 inches that would make better flow. but then again i always hear if it's too wide it slows you down. 3 inches is ok for exhaust though right?? cuzz i have my eyes on HKS. and APS makes the 3.5 what's up with that can anybody explain if the wider the better or ### lol?? n the reason i'm asking about the downpipe is because i'm not going to be using the HKS downpipe because i want a bellmouth so i'm just getting the cat back which is 3 inches and i don't know if turboxs's 4 inch bellmouth would work out for me in this situation. thnx
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#2 Old 12-02-2008, 12:06 AM
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The HKS downpipe is one of the poorest designs for a downpipe. How much are you willing to spend for a downpipe?
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#3 Old 12-02-2008, 12:27 AM
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If you can picture the back part of your turbocharger where the top part of your downpipe connects to it with five bolts, it's sort of an oval shape. That 4" measurement is basically the widest horizontal measurement of that oval. Most bellmouth style downpipes have an opening that wide right where they connect to the back of the turbocharger and then taper down to whatever size the rest of the downpipe is. APS uses 3.5" piping - which I think is the biggest currently on the market right now and is usually reserved for crazy insane horsepower levels, like 600+. Most other companies use 3" piping - which is usually more than big enough for the average street setup.

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#4 Old 12-02-2008, 03:58 AM
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I seriously doubt you would lose any power from going 2.5" (much less 3") unless you are making well over 300whp.

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Originally Posted by man show View Post
If you can picture the back part of your turbocharger where the top part of your downpipe connects to it with five bolts, it's sort of an oval shape. That 4" measurement is basically the widest horizontal measurement of that oval.
I don't think that's true. I think the 4" measurement of the txs downpipe is the actual piping. If you look at it, you'll see that 1. It's freakin HUGE, and 2. It tapers to 3" at the end. Obviously, it can't taper to 3" unless it's initially larger than that.

I would personally never use the txs downpipe because frankly, it looks like a whale's... thing. Stupid reason, but to each his own (i guess).

Anyway, to answer your question, the txs downpipe will not fit. It really has nothing to do with the diameter (since it tapers to 3" anyway). It has to do with the length. The txs downpipe is meant to be used with txs components ONLY, so it will not fit as-is. There is, however, an adapter/extension that you can buy to make it fit on any stock-length catback.
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#5 Old 12-02-2008, 09:35 AM
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But it is true... look at the TurboXS downpipe pic I posted. The top part that connects to the back of your turbo with five bolts is an oval-shaped piece that's 4" wide. The actual pipe that's connected to that cast piece is a 3" pipe stretched slightly so it'll make a smooth transition. The piping itself is not 4".

Also, this is taken directly from TurboXS.com:
"The TXS downpipe is larger than any other WRX/Sti/FXT downpipe on the market. Why is that important? Because, despite what your girlfriend might tell you, size does matter. Turbochargers work best when there is large pressure and temperature differential across the turbine wheel. Having a large, free flowing downpipe is what give you that large pressure and temperature differential. The downpipe has a 4 inch cast bell mouth which tapers to 3 inch towards the flange end."

TurboXS's claim of having the largest downpipe on the market is not entirely true though... APS uses 3.5" piping after their cast section, so technically theirs is bigger.
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#6 Old 12-02-2008, 09:47 AM
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i have a turboxs 4in dp on my 2002 and it is huge. i never had a 3in so i can only compare it to stock and thats not really a fain compairison. mine is 4in all the way down to the flange where it bolts to the mid pipe then it goes from 4in to 3in in the distance of about 4-5 inches. my car compaired to other wrxs with 3in is a considerable difference in the sound of the car. it is a lot deeper sounding with a little more of the boxer rumble also you hear A LOT more turbo spool up. my system is completely catless...hks up.4in down.3in cat delete mid pipe.3in cat back....its a loud system but with the 4in dp you can still hear mostly spool up...i dont really see any disadvantages of the 4in at all.
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#7 Old 12-02-2008, 11:59 AM
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I'll steal a link from Josh. CobbTuning.com - Exhaust Design It's not really needed either, if the DP and rest of the exhaust is designed properly.
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#8 Old 12-02-2008, 12:08 PM
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I believe it's loud. That's what happens when you take a piece of 3" stainless steel pipe and stretch it - the pipe walls get thinner and transmit more noise outside the pipe. It also weakens the structure slightly.

Cobb > TurboXS

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#9 Old 12-02-2008, 01:25 PM
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The design is a little excessive, but there would be no negative effects from it so...........why not?
They consistently put out good power. Don't know why, but you get a lot more of the "turbo whine" out the exhaust note with the bigger 4" DP for some reason (especially catless). First thing i noticed when the Perrin cracked.

I think the whole system they developed with the "swap your cat in 5 minutes" is pretty neat.

You can buy a TXS DP, MP, and Cat (or Race pipe) for cheap on the classifieds. Then buy what ever axleback pleases your fancy.



Also, the taper is within 2-3" from the end of the DP.
At least the one i had was....this one looks like a newer design.

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#10 Old 12-03-2008, 01:23 AM
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oh wow..too much information. ok well not only is that my second time hearing that HKS's downpipe STRAIGHT UP SUX!!! but now i guess i'll just settle for a nice bellmouth with a good rep THAT FITS to the rest of the HKS system lol. cobb is just too dam expensive tho
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#11 Old 12-03-2008, 10:47 PM
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I will be the first to admit that Cobb is expensive. But I can also tell you how happy I am that I saved up for it and got the full TBE. It did suck to have to save up, and the spend that much, but if its what you want, I believe its worth the wait.

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#12 Old 12-05-2008, 05:38 AM
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I have a TXS DP. Works great and fits well.

My name is Ken and I am a HP Junkie.
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#13 Old 12-08-2008, 08:17 PM
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thnx for all the help
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#14 Old 12-08-2008, 08:29 PM
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I had the HKS downpipe, it blows. Gets in the way of the wastegate flapper and causes problems tuning in boost. Now, I have the ERZ bellmouth. It's great, no fitment issues (yeah, it's been disputed but whatever.)

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#15 Old 12-09-2008, 12:05 AM
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Invidia, Megan, Helix, Grimmspeed, they all make great downpipes. You don't need >3" piping with a stock EJ205. Not even friggin close. 2.5" is probably plenty for any setup you have in mind. It's only 2.0L FFS!

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