here's an interesting approach to an external wastegate - Miata Turbo Forum - Boost cars, acquire cats.

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Old 06-04-2009, 01:58 AM   #1
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Default here's an interesting approach to an external wastegate

Modifying an ATR Turbo Wastegate


I'm suddenly overboosting to 18psi when cool out.
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Old 06-04-2009, 06:44 AM   #2
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This isn't really anything new. Us dsm guys have been doing this for quite a while because we used a 2 piece downpipe (think fm style) and a 38mm tial fit perfectly.

example:


In fact, I talked to Corky when my down pipe was being built and asked him about doing the same thing so I could run a tial and use different springs to control my boost instead of a mbc, to which he replied " there isn't much of an advantage to doing this because in the end, you are still relying on the size of the internal wastegate hole to prevent boost creep." You can port it out a bit, but its risky business as it will eventually crack if you port it too much.
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Old 06-04-2009, 09:33 AM   #3
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This is how Cjernigan's first setup was, he didn't have boost control issues.
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Old 06-04-2009, 02:53 PM   #4
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The biggest disadvantage w/ this setup is flow quality at the turbine exit, probably doesn't amount to anything though.

I couldn't do this w/ mine, as the wastegate port can't be sealed to the housing (big cavity.)
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Old 06-06-2009, 01:40 AM   #5
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My S5 manifold doesn't have boost control issues, yet.
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Old 06-15-2009, 05:40 PM   #6
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Think space would permit something like this on a BEGi DP?

Is welding to cast more prone to cracking (ie BEGi's ex.manifold w/ ext wastegate)?
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Old 06-15-2009, 05:59 PM   #7
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yes, it is more prone to cracking.
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Old 06-15-2009, 06:20 PM   #8
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Quote:
Originally Posted by Jeff_Ciesielski View Post
"in the end, you are still relying on the size of the internal wastegate hole to prevent boost creep."
Right, but the flapper is gone too. That helps.
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Old 06-15-2009, 07:17 PM   #9
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I love this design from ATP... clean and Vband.
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Old 06-15-2009, 07:52 PM   #10
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We (CAT) tried that on a few engines and it worked well until the weight started to "stretch" the casting/machined sealing surface of the WG flange.
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Old 06-15-2009, 10:45 PM   #11
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Quote:
Originally Posted by samnavy View Post
I love this design from ATP... clean and Vband.
suposedly those really screw-up spool-up.
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