Fabricate a Bell-Mouth Opening on a Stromung Downpipe? Whaddya Think?
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This is a discussion on Fabricate a Bell-Mouth Opening on a Stromung Downpipe? Whaddya Think? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; I've been waiting and waiting for one of the component exhaust systems, namely Stromung and ScoobySport to create a downpipe ...

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    Fabricate a Bell-Mouth Opening on a Stromung Downpipe? Whaddya Think?

    I've been waiting and waiting for one of the component exhaust systems, namely Stromung and ScoobySport to create a downpipe with a cat. Thing is, Stromung makes a downpipe with a cat with a stock style opening that blocks the wastegate. ScoobySport makes a one with a great bell-mouth opening, but with no cat. I know that Graham Goode Racing makes a component system with a downpipe that has a cat AND a bell mouth opening, but after my experience with their up pipe, I'm wary of their fitment since it was created for UK-spec WRXs. But I've come into contact with a local fabricator with a good reputation, so I'm thinking of just handing a Stromung downpipe over to them, and having them create a bell-mouth opening as it is on the Graham Goode Racing downpipe.

    Allow me to illustrate:

    This is the Stromung downpipe. Note how there's only a hole for the exhaust outlet out of the turbo, and how the wastegate would just hit that steel wall next to the hole. But it has a cat!


    This is the bell-mouth opening on the ScoobySport downpipe next to the stock downpipe. But no cat on the ScoobySport!


    This is the Graham Goode donwpipe with a cutout for the wastegate and a flanged add-on on the piping. Nice idea, eh? With a cat! But not U.S.-spec. For example, what the hell is that sensor inlet right after the cat doing there?


    Here's a nicely detailed photo of the stock downpipe juxtaposed to a beautiful, if catless, downpipe with a bell-mouth.

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    Moderating on the run! Big Sky WRX's Avatar
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    bedabi,

    There may be a fair amount of interest in a project like this, depending on how the SEB rules on the cat/precat issue for STX. Right now we're hearing encouraging words that it might go to something along the lines of must maintain one cat (or replace w/ a high flow) and must be able to pass federal emmission stds.

    Barring that change, I most certainly would be interested, maybe even if they change it (still need one cat and that one would prevent any cels).

    Bell mouth (ala scoobysport) definitely the way I want to go. Please let us know what you find out. By the way what does the Stromung down pipe cost?

    Thanks

    Big Sky

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    A slight modification in plans. I know a great Subaru installer who has a bunch of stock downpipe leftovers from folks who decided to just lave the behind after installing new pipes. So I'm gonna just buy one off of him and have someone fabricate a bell mouth to that.

    I spoke with Bill at http://holeshotperformance.com who told me that fabricating a bell mouth would be easy. They would simply weld on new piping at the top of the downpipe, where the cat starts up to the lip where the downpipe attaches to the turbo. But he said the most difficult part would be finely matching up the new downpipe bell mouth to the turbo.

    In all, he estimated that the labor and material would cost me about $150. If he could pull it off, it sounds pretty good, doesn't it?

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    Modifying a stock down pipe still will not address the issue of the highly restrictive stock cat. I have only theory to back up my statement but a bell mouth design and larger diameter piping will do little to aid in performance. Your original modification of the Stromung downpipe is a great idea if cost effective.
    I second Big Sky’s comments. Hurry up SCCA.....

    Shawn

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    Moderating on the run! Big Sky WRX's Avatar
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    I'm sure the bell housing would help some, but I agree w/ scurry that the high flow cat, combined w/ the bell housing, would be the way to go. Anyone know what the Stromung downpipe goes for, the Scooby Sport is ~ $330.

    Big Sky

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    Thanks for your input, everyone! Yeah, I think you're right. I'll go with Stromung after all.

    I'll be getting mine from Teague's Auto. http://home.att.net/~teaguesauto/index.htm

    The Stromung downpipe with cat is $259. A catless downpipe is $199.

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    Moderating on the run! Big Sky WRX's Avatar
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    Are you still going to try for the bell mouth? I think it would be worth if not too expensive.

    Big Sky

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    Registered User z3coupe's Avatar
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    Well, as you already know, its 94% certain that we now CAN remove 2 cats in SCCA. Howard even said I would be safe to do this mod for the PRO Solo this weekend, if only I was now going to it (you know, my Mother passed away, going back home Tuesday). So bye bye up-pipe precat!

    But now, . . . . . which is really better? The open bell housing, or the divided one like the MRT one? Vishnu seems to like the divided way, and even went a step further to have a completely separate pipe for the wastegate than even bypasses the cat.

    Anyway, I will have these questions in my new post, please look at it and answer there if possible?
    Rocky Zamarocy
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    Registered User superhawk44's Avatar
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    dyno?

    Has anyone done any dyno testing of different downpipes? I think it would be the deciding factor. What about the old butt dyno,anybody driven simmilar cars with different downpipes? I bet the spool up time is quicker without the divider,but I still think someone should do a dyno test with differnt ones. There must be a shop that has some numbers from different d-pipes. Plus isn't the txs pipe alot bigger than most others? I am looking hard at theirs. Oh well just my $.02,CHRIS......
    WR Blue,STi short throw
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    I have a Stromung downer which I purchased a few weeks ago. As I await the completion of a FP turbo modification and the return of the modified core, I have requested my mechanic to modify the Stromung down pipe as I expect boost spikes which I would not have expected with the stock turbo.

    While I do not plan the addition of a cat, I'll report the results.

    Russ

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    Registered User z3coupe's Avatar
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    Well, as far as I know, Stromung, who WAS SUPPOSED TO WORK WITH ME ON THIS as I am local to him, and kept telling him about the cat and the bell mouth - never followed through with it. He never answered my calls or messages - and it still seems he uses the stock flange - DUH!!!! So I went with Ian at PDE. Now at this moment, we have a cat-less D/P that is working great. And it has a bell mouth - but beware. Ian explained to me that those, like the MRT or Goode mentioned above that have an extra part welded on could have cracking problems later on. You see, the weld is of different material as well as thickness - it heats up and cools down at different temps than the rest of the metal. And this is at a critical spot - right next to the red (or white???) hot turbo where the temps are extreme. PDE does not weld anything extra on theirs other than the bracket - but does have a bell mouth. As for the cat - that is still in the works. Sadly, he is quite busy, and some cat suppliers are being non-cooperative. Ian won't let it be sold unless it is just right - which impresses me.

    Now, we have not dyno'd anything yet, but lets just say that out on the AutoX course, I no longer have any urges to try and shift into 1st gear anymore!!!!
    Rocky Zamarocy
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    Moderating on the run! Big Sky WRX's Avatar
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    Rocky

    Your alive! I thought you may have joined the French Foreign Legion.
    Glad to see you back.

    Mike

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    Registered User z3coupe's Avatar
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    Heheheh thanks Mike. Well, the way I found out I lost 11 years of my life being used by the ex GF while she still had her kids, the Legion sure was a viable option. That, and the fact that I still can't seem to get out of 4th place hell here is killing me. Its not the HP or lowend - its the damn understeer I can't seem to get rid of. I guess I might have to think about removing the FREE prototype front swaybar, cause it seemed to start after that was on. But it is really hard to refuse something that is free
    Rocky Zamarocy
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    Registered User All8up's Avatar
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    Originally posted by russ
    I have a Stromung downer which I purchased a few weeks ago. As I await the completion of a FP turbo modification and the return of the modified core, I have requested my mechanic to modify the Stromung down pipe as I expect boost spikes which I would not have expected with the stock turbo.

    While I do not plan the addition of a cat, I'll report the results.

    Russ
    When I had a TD04 on the stock DP w/ elevated boost levels (set @ 15psi), I would get some boost spikes in between shifts. Since switching to a VF30 and TurboXS DP, I do not see those spikes/surges anymore.
    Good luck w/ your FP upgrade, let me know how it goes.
    e46 M3 (new toy)
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    MisterX's Avatar
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    I just received a quote on this of about $250.

    I'll talk to my muffler guy locally, too. Sounds like a lot of money to spend on a problem that doesn't exist yet.

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