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Old 02-07-2018, 12:17 PM   #1
Scooby Newbie
Member#: 466924
Join Date: May 2017
Default EWG placement help - or twin scroll... hmm

Hey guys, what's up.

New on here, but not to subarus by any means, have had 6 of them, modifying all. Currently still have 2 SH9 foresters, both 2.5 XT. One for wife (stockish), one for me (modded).
From UK so these are RHD cars, which prove some problems. Which is what leads me here, need to discuss external wastegate locations... hmm
Been viewing on here for years, usually find what the info I need. In this case I can't find it.

Basically I'm chasing 400whp, and assume all supporting mods; purely talking turbo setup here.

I narrowed this down to 2 choices;

Get the tomioka racing twin scroll turbo kit,
Stick with upgraded single scroll.

On one hand, the twin scroll is far better any way you look at it. However, what holds me back is the equal length headers, so in turn lose the boxer rumble. That might sound like a small sacrifice to make, but to me it's a big one. Especially when I'm running a boost activated exhaust cut out. I love the sound! It's also internally gated, which leads me on.

If I was to stay single scroll, like a Blouch etc. I would want to go EWG and I would plan to keep the OEM headers and mod them as follows;
Port and polish - I'm handy with a dremel.
Upgrade Up pipe,
Upgrade crossover/X pipe.
Now remember this is a RHD car so placement of a EWG on the up pipe is a pita. So here's the main question...

Would it be possible to run the EWG on the x-pipe. I know it goes against flow for the right side cylinders. Not saying this is the most suitable, effective or efficient way of doing it...
BUT would it work? Thoughts?

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Old 02-07-2018, 12:17 PM   #2
Scooby Newbie
Member#: 466924
Join Date: May 2017

Or has anybody seen or done this?
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Old 02-07-2018, 01:04 PM   #3
Scooby Specialist
Member#: 298403
Join Date: Oct 2011
Chapter/Region: W. Canada
Location: Alberta, Canada
2008 WRX Premium
Spark Silver


Putting the EWG on the cross pipe would not be a smart idea, especially if you're shooting for 400 hp. Reason is because of manifold pressure and exhaust flow.

Exhaust flows one way. It doesn't matter what cylinder or bank it's coming from, it's flowing away from the heads. Part of the flow from Bank 2 (cyl. 2/4) would divert through the WG and part would continue on in the x-pipe, while the flow from Bank 1 (cyl. 1/3) would essentially have to double back, fighting the flow from the opposite bank, if it's able to do so at all. Ideally, you want the WG bleeding pressure downstream from the collector from all cylinders. Putting it in the x-pipe would likely effect spool times and may have difficulty maintaining boost because exhaust pressures between banks cannot be regulated equally.

In the case of most twin scroll setups, you'd need an EWG after the collector for each group of cylinders, so two EWG's. If it's IWG, how ever many gates the turbo has (if it has) will suffice as the turbine housing is the collector for both of the up pipes.

It seems you don't really have a decision to make that doesn't come without a sacrifice.

You need ELH for twin scroll. Pros: significant power gains. Cons: cost may be higher. Sacrifice: may lose boxer rumble.

Keep boxer rumble. Pros: cheaper cost as the factory header is a good unit compared to aftermarket UEL. Cons: exhaust flow and efficiency not as good as some aftermarket ELH. Sacrifice: not as advantageous for power gains. Still possible, but harder to make.

Killer B holy headers seem to maintain a lot of boxer rumble. May be worth a look if you can have your cake and eat it all in one go.

Last edited by viper_crazy; 02-08-2018 at 11:44 PM.
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Old 02-07-2018, 01:19 PM   #4
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Member#: 466924
Join Date: May 2017

Thanks viper crazy,

Your right, didn't think about that. Hmm back to square one.
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Old 02-25-2018, 03:11 AM   #5
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Member#: 448078
Join Date: Jun 2016

You can get a custom ewg done for your twinscroll set up .you'd have to tap off each uppipe runners and merge into a single wastegate or tap each uppipe runner and run two wastegates. The cost may not justify the benefit depending on your goals.
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