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Old 12-14-2010, 04:17 PM   #1
rollertoaster
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So I bought a used shorty DP off another forum and and now I know why the person was selling it. I wanted a shorty to keep my stock rear cat because I need the car to be quiet. I don't really like how bellmouth DP's merge so close behind the turbo. My main problem with this downpipe is that when the cut the hole in the main pipe for the recirc to come back in it was only a small circle. It should have been cut to an oval shape to match the intersecting recirc pipe. I'm not even going to put his on my car because by the looks of it I will be fighting boost creep, due to the bottleneck on the recirc tube. Sigh...

If I wanted to fix this one I would have to cut the pipe after the intersect and grind the hole out the re-weld the pipe back together. I'm not sure I even want to bother with that.
I guess I'm just going to have to make my own. That's what I get for being lazy.

Does anyone have any experience with the Perrin shorty? Do they grind out the recirc merge correctly or just slap it together?

Where can I get a decent turbo stainless turbo flange that I can weld a 3" pipe to? Or even 3.25", I have a special stash of thickwall bends that I would like to use
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Old 12-14-2010, 08:39 PM   #2
ZeroDrift
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Picture didn't post.

I've had good luck with this vendor for exhaust flanges and other parts: http://www.vibrantperformance.com/main.php
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Old 12-14-2010, 09:15 PM   #3
rollertoaster
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Quote:
Originally Posted by ZeroDrift
Picture didn't post.

I've had good luck with this vendor for exhaust flanges and other parts: http://www.vibrantperformance.com/main.php




Hopefully it worked this time.

I tried vibrant's site and didn't see any subaru flanges. Unless they are interchangeable with one of the Garrett flanges??
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Old 12-14-2010, 09:25 PM   #4
ZeroDrift
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If it were me, I'd cut the opposite end of the pipe and enlarge the dump tube exit. A patch shouldn't be too difficult/expensive to weld back on.


-Just realized what flange you want: stock turbo to downpipe flange, right?

Not sure of where, but if you search in this forum or the built engine forum I'm sure I've seen a thread w/ vendors that carry OEM flanges.
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Old 12-14-2010, 09:30 PM   #5
TRSCobra
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Aftermarket manufacturers spend thousands in R&D and almost all of them utilize a bellmouth design. Why do you feel that it's not a good one? All those "divorced" WG downpipes do is create a wall in between the pipes that the exhaust slams into.

Unless you can completely close off the IWG from the turbine exit, the best idea is bellmouth. And ANY bellmouth DP would be better than that one.
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Old 12-14-2010, 11:42 PM   #6
downest
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I can get you a flange, I have them laser cut once in a while for Honda turbo kits using Subaru turbos. I may have one in 304 stainless, 1/2" thick right now, I can check when I go to the shop tomorrow morning.
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Old 12-15-2010, 11:11 AM   #7
rollertoaster
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'I can get you a flange, I have them laser cut once in a while for Honda turbo kits using Subaru turbos. I may have one in 304 stainless, 1/2" thick right now, I can check when I go to the shop tomorrow morning."

Thanks, Pm if you have one to spare. I found a seller on ebay, but I'm sure its not the best quality. I'd prefer something not cast as welding will be easier that way.

Everything I've learned about turbos and wastegates from my own experience buidling downpipes leads me to stay away from bellmouths. I understand that the difference is minimal if at all, and that it is impossible to build a true divorced system on the stock turbo due to the turbine housing construction. I do plan on adding a divider to the downpipe flange though. I also plan to intersect the wastegate back in at an angle of 45degrees or less no closer than 18" behind the turbo.

I know I can cut the downpipe that I have and grind out the hole the re-weld it back together. However that will require me to make a jig to bold it to so that everything lines up properly when I am finished. I started making the jig and figured I may as will just make my own DP from scratch using the jig and sell the DP that I have to someone else. Even if I do fix the intersect, I'd still be stuck with a 2.5" turbine outlet pipe.

My reasons for making my own are more based on just wanting to do it for myself. I just like to fabricate stuff and will be happier with the final outcome if I can control process myself.
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Old 12-18-2010, 04:39 PM   #8
konmann
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Toaster,

Ive had to do the same thing with my down pipe (MadDad V2 catted 2 piece) you want to do with yours. The welder just cut the wastegate tube off, enlarged the hole you pictured in the proper direction allowing the cut off tube to be repositioned (slightly higher) on the main pipe. I also had them finish weld the mating surface side of each flange. I felt this would prevent the hot exhaust gasses from chewing away at the single weld from the backside and eventually cracking the downpipe in this area due to heat stress.

The cost was somewhere around 200$ for all of the work.

If the downpipe fits reasonably well now, it may be worth your time and effort to slightly alter the down pipe rather than havng to start from scratch. If you want to keep the wastegate pipe in the same position, get a mandrel bent sectiion of pipe (I think 1.5" diameter) and replace the section that is cut off the original dp.

Laastly if you can do it, samd/grind the flange mating surfaces flat after the welding is complete. This will lessen the amount of headaches you'll have with gasket sealing. I've got a thread with pictures about that in this section.

Regards,


Konmann

Any questions please PM me. I have had the altered downpipe on the car for about 20,000 miles no problems.
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Old 12-18-2010, 04:46 PM   #9
Uncle Scotty
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with the stock last cat in the system....nothing you do will make much difference

that last cat is a REAL flow restriction

I have used it and not used it and do NOT use it


all it is is a butt plug in the system
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Old 12-18-2010, 08:15 PM   #10
rollertoaster
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Quote:
Originally Posted by Uncle Scotty
with the stock last cat in the system....nothing you do will make much difference

that last cat is a REAL flow restriction

I have used it and not used it and do NOT use it

all it is is a butt plug in the system
Haha, thanks for the advice Scotty. Maybe I'll explore other options, not totally sure yet.

Konman. I'm capable of doing the welding myself and once my jig is complete I probably will. I was just going to cut the main pipe just behind the recirc and grind out the recirc the from the inside. Then weld the pipe back together. I may use the DP after i fix it but, then again I may sell it to some one else and build my own, just to keep my fab skills fresh (and I'd like a 3" main pipe). Oh and I have a friend with a mill, I always have him make a pass on all my flanges after welding to take care of any warpage.
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