TBE: Cobb vs APS vs Lachute(custom) - Page 2 - Subaru WRX Forum
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post #16 of 24 Old 12-01-2008, 10:42 AM
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Good eye sir, good eye.

Thanks

Meth'd, EWG'd, Str8 Cut PPG'd, 20G'd Bug-i, 354awhp and 315tq SAE 5 Corrected 50/50 meth @ 19-20psi.
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post #17 of 24 Old 12-01-2008, 02:21 PM
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This is ridiculous... have you guys ever tried opening an iwg with your hand by pulling on the arm? Fully open = 45 degree angle. It cannot, and does not FULLY open. What does that mean? The gases don't go straight out. They hit the wastegate door and move towards the direction of the turbine gases. Sit down and THINK about the implications of this.

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Semi or divorced DP are just not as proven as a full Bellmouth. Well divorced in theory (turbulence) are suppose to be better but i'll take my bellmouth.
This is COMPLETELY false. There is no proof to back up this claim. PDE, a very reputable company, makes a semi-bellmouth downpipe and I have NEVER heard anyone claim that it will give 1 less hp than anything else. What matters is that the opening of the downpipe is large enough to clear the wastegate. As long as the downpipe fits this criteria, the only "wall" the wastegate gases will hit is the wg door itself. If you want to claim that the larger volume of a full bellmouth downpipe gives it the advantage, then clearly the txs dp would make more power than everything else, and we should simply ignore cobb, invidia, helix, etc.

Divorced wastegate downpipes are a WASTE OF TIME. Seriously, look at your turbo and try to imagine where the wastegate gases might end up going. It's obvious that they won't go straight into the separate pipe because of the fact that the door does not open all the way. The only "true" divorced wastegate design would consist of something like an aps turbo with the divider integrated into the turbine housing. Anything else labeled "divorced" completely fails at doing what it was designed to do. They do NOT separate the gases. On the contrary, I bet they create more turbulence than anything else.

Last edited by WReXd; 12-02-2008 at 04:31 AM. Reason: terminology error
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post #18 of 24 Old 12-01-2008, 04:17 PM
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Originally Posted by WReXd View Post

If you want to claim that the larger volume of a full bellmouth downpipe gives it the advantage, then clearly the txs dp would make more power than everything else, and we should simply ignore cobb, invidia, helix, etc.

Divorced bellmouth downpipes are a WASTE OF TIME.
I am not a fan of divorced or semi's sorry.
There DPs work in theory but in practical application time and time again a full bellmouth put out better numbers with bigger turbos.

Stock to mild turbos usually have no difference. You get to a big 18g, green, dom 3 or 4, the divorced does nothing but supply a restriction (creep most times).......period.

You send me a divorced i'll slap it on the dyno on my power map and prove my bellmouth puts out more.

Meth'd, EWG'd, Str8 Cut PPG'd, 20G'd Bug-i, 354awhp and 315tq SAE 5 Corrected 50/50 meth @ 19-20psi.
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post #19 of 24 Old 12-01-2008, 05:25 PM Thread Starter
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Quote:
Originally Posted by WReXd View Post
This is ridiculous... have you guys ever tried opening an iwg with your hand by pulling on the arm? Fully open = 45 degree angle. It cannot, and does not FULLY open. What does that mean? The gases don't go straight out. They hit the wastegate door and move towards the direction of the turbine gases. Sit down and THINK about the implications of this.


This is COMPLETELY false. There is no proof to back up this claim. PDE, a very reputable company, makes a semi-bellmouth downpipe and I have NEVER heard anyone claim that it will give 1 less hp than anything else. What matters is that the opening of the downpipe is large enough to clear the wastegate. As long as the downpipe fits this criteria, the only "wall" the wastegate gases will hit is the wg door itself. If you want to claim that the larger volume of a full bellmouth downpipe gives it the advantage, then clearly the txs dp would make more power than everything else, and we should simply ignore cobb, invidia, helix, etc.
This is exactly what the guy at Lachute Performance told me and showed me on a VF-39.
Their DP covers half the waste gate door, leaving enough room for it to open and let gases flow in the down pipe. I'm glad to here someone else say it.

WRX_Fan_0717, you have a very clean car indeed. Very nice!
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post #20 of 24 Old 12-02-2008, 04:42 AM
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Quote:
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Their* DPs work in theory but in practical application time and time again a full bellmouth puts* out better numbers with bigger turbos.
*Edited for grammar
That may be true, but at that stage you shouldn't even be considering iwg. For applications that matter (stage 2-mild upgrades) there is no difference.
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the divorced does nothing but supply a restriction (creep most times).......period.

You send me a divorced i'll slap it on the dyno on my power map and prove my bellmouth puts out more.
That is exactly my point...
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post #21 of 24 Old 12-02-2008, 09:58 AM
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I have the maddaa dp . Fit is A+ . I would go either way for the Dp . DWG or BM but no partial nonsense . Cobb is always an excellent choice .

-NICK-
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post #22 of 24 Old 12-02-2008, 11:16 AM Thread Starter
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Originally Posted by WRX_Fan_0717 View Post

Stock to mild turbos usually have no difference. You get to a big 18g, green, dom 3 or 4, the divorced does nothing but supply a restriction (creep most times).......period.
When you say stock to mild turbos, do you mean any of the IHI VF series turbo and any 16g?
I don't think I'll ever go bigger than that.
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post #23 of 24 Old 12-02-2008, 11:53 AM
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*Edited for grammar
That may be true, but at that stage you shouldn't even be considering iwg. For applications that matter (stage 2-mild upgrades) there is no difference.

That is exactly my point...
Edit my grammar all you like. You might be a little busy because i'm from the South and also barely passed E-Comp 2. But aced Calc2......funny how that works. !Notfunny!

I think we have been arguing over semantics.........We've basically said the same thing.

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Originally Posted by WRXDre View Post
When you say stock to mild turbos, do you mean any of the IHI VF series turbo and any 16g?
I don't think I'll ever go bigger than that.
Pretty much. However, the EVO3 16G i would start thinking Bellmouth.

Meth'd, EWG'd, Str8 Cut PPG'd, 20G'd Bug-i, 354awhp and 315tq SAE 5 Corrected 50/50 meth @ 19-20psi.
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post #24 of 24 Old 12-21-2008, 06:54 PM Thread Starter
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Hi guys, sorry for bringing back a dead thread, but I found some information on the "semi-bellmouth" design downpipes that I think might be interesting for some of you.

It's a post from the fabricator at Lachute Performance, its in french but the pictures definitely speak for themselves.

Montreal Subaru Club :: Voir le sujet - Comparo "semi-belmouth" Lachute VS OEM **Photos**

First picture is to show the difference between OEM vs Semi

Second shows the wastegate door fully opened and again OEM vs Semi with fully opened wastegate door.



Basically what he is saying is that Lachute Performance always went with the "semi-bellmouth" design because after all the dyno tests that they did, it NEVER made LESS power than a traditional "bellmouth". And that if they would have seen a power loss from that design they would have changed it a long time ago.

***Also mentioned that if they didn't see any difference it doesn't mean there is none. They just think that the difference between the two is nonexistent and can be neglected.

Now the point that they always defended is has stated above, that the wastegate door opens up and deviates the gases in the exhaust flow. Making the semi vs bellmouth equal, unless used with a TWIN SCROLL turbo, because the wastegate door opens up the other way.(then a full bellmouth would be more effective.)
If you look at the third reply there's a picture of a VF37 twinscroll.



I hope maybe some of you learned something from this. I know i did!



Dre

Last edited by WRXDre; 12-21-2008 at 08:27 PM.
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