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Old 02-07-2009, 07:16 PM   #1
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Default External wastegate - Pros and Cons

I am considering either an external wastegate or a divorced dump tube from the existing internal wastegate.

The reason is that I have a very flat (apparent) torque curve above 5k RPM and I think that's because of the tiny turbine on the TD04-13T. I dont remember the exact numbers but my injector duty cycles from 5k to 7k rpm dont really increase as much as some others here.

So, for those of you who went from internal to external wastegate, what are the general effects you experienced on

1) peak power (this is fairly well understood)

2) boost threshold

3) lag above the boost threshold

4) Ease or difficulty of tuning the EBC map.
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Old 02-07-2009, 07:30 PM   #2
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Internal Wastegate
pros: cheap
cons: everything else
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Old 02-07-2009, 07:56 PM   #3
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External wastegate
pros: everything
cons: cost more and takes longer to setup......... But sooo worth it.
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Old 02-07-2009, 08:49 PM   #4
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plus you can run a glorious open dump with an external gate.
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Old 02-07-2009, 10:28 PM   #5
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i was expecting a more....technical discussion.
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Old 02-07-2009, 10:33 PM   #6
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internal wastegates flow poorly, they don't control boost well, they don't seal very well....

external wastegate flow well, they are very good at controlling boost, and they seal very well.
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Old 02-07-2009, 10:34 PM   #7
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Quote:
Originally Posted by The_Pipefather View Post
i was expecting a more....technical discussion.


I saw brain's comment and I couldn't help myself.

Only things an internal gate does better is possibly pull more evenly from each cylinder. And it's cheaper.

External gate is the better part in most regards. With a dual port external gate, you can set it up so that even with a MBC, it stays 100% PINNED ******* SHUT till you reach 2-3 PSI of your target boost. So it's not much worse than EBC, especially if you run a higher boost. The ideal setup is EWG, stiff spring, dual port, diaphragm type MBC. I need to get a diaphragm type MBC (read, air pressure regulator from lowes for 5 bucks) and hook mine up this way.

Also external gates have a bigger valve so they're less likely to overshoot boost, more stable boost control, etc. Everything sums it up.
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Old 02-07-2009, 10:45 PM   #8
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Where can I get one of these external wastegates? Can I haz one for my n/a setup?

This does have the thinking, which is always, always bad. Can one make an internally wastegated turbo into external as easily as welding up the internal, and going with an external mount manifold? Anything need to be done in the downpipe area where you would still have a large bell opening (or s/g) for the no longer functioning wastegate? Seems like you would end up with some turbulance. Im thinking in terms of like a 2560.

Sorry for the highjack, but it really already has kind of been answered hasnt it?
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Old 02-07-2009, 10:53 PM   #9
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Quote:
Originally Posted by NA6C-Guy View Post
Where can I get one of these external wastegates? Can I haz one for my n/a setup?

This does have the thinking, which is always, always bad. Can one make an internally wastegated turbo into external as easily as welding up the internal, and going with an external mount manifold? Anything need to be done in the downpipe area where you would still have a large bell opening (or s/g) for the no longer functioning wastegate? Seems like you would end up with some turbulance. Im thinking in terms of like a 2560.

Sorry for the highjack, but it really already has kind of been answered hasnt it?
Yeah, that's what people do. Weld the internal gate's opening shut and add an external gate. Currently, there aren't many options for manifolds with external gates. I had to add my own port to my FM manifold for my 38mm EWG. Also braced it to be safe. As for the downpipe, I'd leave it alone. It's not gonna make much difference if it's still bell mouthed.
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Old 02-08-2009, 12:42 AM   #10
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I just came in from the garage after looking at a WRX turbine housing and thinking about this very question.

Don't take this the wrong way, your build thread has really helped me with my motivation and planning. Just trying to be helpful.

I couldn't find any posts suggesting you've changed this yet, and it's a much bigger problem than an internal wastegate:



Quote:
So I decided to keep it simple for now, and thus the flange is just a flat plate.
The flat plate causes the wastegate flow to have to join the main turbine discharge flow at a 90-degree angle. That screws up the discharge flow itself. The wastegate flow, and some of the turbine discharge, has to make a 90-degree turn to get down the undersized downpipe, and its early-apex approach to the corner further chokes the available flow path. Build a 2.5" downpipe with a proper bellmouth before worrying about what kind of wastegate you have. Yes, going to an external wastegate would solve this problem, but mainly because you'd be bypassing it. It's a lot easier and cheaper to just fix the downpipe.

Once you have a good bellmouth and not just a flat plate with a round hole, you could have a section of 2.5" tubing welded in the turbine housing at least up level with the gasket surface, or even a bit higher if you're careful. Then port the turbine discharge out to this wall. It's kinda like what Garret's done on some versions of the GT2560R. This will prevent the wastegate flow from making an incursion into the main charge stream until it's already headed in the right direction, significantly reducing the disruption to the turbine discharge flow.

Or, as you mention, you could just do that divider wall and then add a divorced wastegate tube. Might be easier to add that to your existing downpipe if you really want to keep it.
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Old 02-08-2009, 01:48 AM   #11
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Quote:
Originally Posted by SolarYellow510 View Post
I just came in from the garage after looking at a WRX turbine housing and thinking about this very question.

Don't take this the wrong way, your build thread has really helped me with my motivation and planning. Just trying to be helpful.

I couldn't find any posts suggesting you've changed this yet, and it's a much bigger problem than an internal wastegate:





The flat plate causes the wastegate flow to have to join the main turbine discharge flow at a 90-degree angle. That screws up the discharge flow itself. The wastegate flow, and some of the turbine discharge, has to make a 90-degree turn to get down the undersized downpipe, and its early-apex approach to the corner further chokes the available flow path. Build a 2.5" downpipe with a proper bellmouth before worrying about what kind of wastegate you have. Yes, going to an external wastegate would solve this problem, but mainly because you'd be bypassing it. It's a lot easier and cheaper to just fix the downpipe.

Once you have a good bellmouth and not just a flat plate with a round hole, you could have a section of 2.5" tubing welded in the turbine housing at least up level with the gasket surface, or even a bit higher if you're careful. Then port the turbine discharge out to this wall. It's kinda like what Garret's done on some versions of the GT2560R. This will prevent the wastegate flow from making an incursion into the main charge stream until it's already headed in the right direction, significantly reducing the disruption to the turbine discharge flow.

Or, as you mention, you could just do that divider wall and then add a divorced wastegate tube. Might be easier to add that to your existing downpipe if you really want to keep it.

I am having trouble following your post. First, whose build thread did you take that quote from? PatsMx5? On the setup I am working on, I am going to use an external wastegate and using a flat flange. Now the turbo I am using does not have that space in the turbine exit like what you see on the exit of the turbo below. I can see that being a problem with using an external wastegate unless you plugged up the hole. Then it would not be the "best flow" but it would be "ok"




Here is the setup I am going to use:



I suppose the wastegate hole (which will be covered by the flange) might cause some turbulance, but i am not all that worried about it. I know that there are plenty of folks who run it like that with no issues.
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Old 02-08-2009, 01:53 AM   #12
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That's not my dowpipe in the pic. My ****'s Wayyy bigger than that.
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Old 02-08-2009, 02:06 AM   #13
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Pic is from PF's own build thread.
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Old 02-08-2009, 02:09 AM   #14
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Pipefather,

External gate controls boost way more presisely. Dont know about power gains from it over an internal, but I wouldnt think them to be that big. They cost money and a bit more work to plumb in (assuming you dont already have a ewg ready setup)
Internal is OK but definitely not as precise or good as external. I chose to go internal on my setup, just for the simplicity of having it on the turbo and what not. I know, not a really good reason but w/e.

As far as your car/setup, I would HIGHLY suggest getting a bellmouth style downpipe. Solar yellow is absolutely right: the biggest cork in your setup is not the internal gate, it is the downpipe you are using. WRX's using same turbo gain a SIGNIFICANT amount of power from a bellmouth downpipe compared to the one you are using, especially up top where you say you can use a bit more.

Take a look at mine, it is nowhere near ready or great, but I can guarantee you that swapping yours for something like this, or modifying it will prove to be a great benefit:



Just my .02
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Old 02-08-2009, 03:15 AM   #15
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Not sure why, but bellmouths from BEGI/FM would always crack...over and over. Is there some inherent flaw w/ the bellmouths or is it just craftsmanship?

I was told that's why BEGI stopped doing the bellmouth.
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Old 02-08-2009, 03:17 AM   #16
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Absolutely, if you are running an internal gate and the wastegate exits into a flat wall less than an inch away its going to be a bottleneck. The Begi-s setup is designed that way fwiw.
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Old 02-08-2009, 03:21 AM   #17
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Quote:
Originally Posted by kenzo42 View Post
Not sure why, but bellmouths from BEGI/FM would always crack...over and over. Is there some inherent flaw w/ the bellmouths or is it just craftsmanship?

I was told that's why BEGI stopped doing the bellmouth.
there are a gazillion wrx's running all kinds of different bellmouth downpipes from cheap to extremely expensive and I have not heard of a single reported crack from a single one of them.

I can only assume bad craftsmanship on BEGi's part
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Old 02-08-2009, 05:28 AM   #18
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yea i just picked up a tial 40mm on a ss o2 housing with a dump tube for 250 bucks, it looks sick and im sure it will work way way better the tiny *** internal gate in my hahn 16g.
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Old 02-08-2009, 05:48 AM   #19
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Now back to the original topic. From the couple of years i've been learning about turbo's, heres my take:
Internal wg - enough for most setups, cheaper and simpler
External wg - more precise, possibly better spool, costs more, more complex
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Old 02-08-2009, 10:45 AM   #20
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Quote:
Originally Posted by 18psi View Post
there are a gazillion wrx's running all kinds of different bellmouth downpipes from cheap to extremely expensive and I have not heard of a single reported crack from a single one of them.

I can only assume bad craftsmanship on BEGi's part
Isnt the stock downpipe just a plate and a tube on a wrx? which explains why people upgrade to a bell mouth.
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