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7.0:1 > 11.3:1
 
Join Date: Oct 2003
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Turbo Braintrust - Question about Wastegate Placement

I'm building a single turbo system for my 993 and though I've got a split vane housing I only intend to use a single wastegate.

Reading everyones opinions over the last few months I've come to realize I won't be taking full advantage of the split vane aspect of the turbo by using a single wasgate. However I've realized I have two locations to tap the wastegate. First picture, and how I originally intended to place the wastegate has it's port right at the flange to the turbo. I then realized I could tap into each exhaust runner prior to the elbow leading up to the turbo, which is more work but I really don't know if it would add to keeping the paulses split. See the second picture where I've drawn a black circle showing where could tap into the exhaust runners.

Am I OTL thinking there would be any advantage to the second scenario?

The wastegate valve is sitting on top of the bottle in the first picture, and it's location would be similar in the second scenario as I want the exhasut routed to the muffler.






Last edited by Jim2; 09-11-2010 at 03:02 PM..
Old 09-11-2010, 02:47 PM
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Turbo Hooligan
 
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I would go with the 2nd scenario. if you just graft on the wastegate pipe at the base or the turbo i promise you'll have boost creep in higher gears. not sure about the twin scroll aspect, maybe rarly could chime in on that
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Old 09-11-2010, 04:25 PM
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Crotchety Old Bastard
 
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That's a great looking system Jim. I agree you should go with the dual WG pipes, the single will negate the design of your your split plenum and it is a very bad angle.
I don't know where you are planning to put the waste gate but you should consider using the same split plenum treatment on the single waste gate collector. You then retain your true split system but with only one waste gate.
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Old 09-11-2010, 06:09 PM
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7.0:1 > 11.3:1
 
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In my second scenario I thought of merging the two about 4" prior to the wastegate.

So what you are saying then, is keep the two wastegate inlet pipes segregated right up to the base of the wastegate?
Old 09-11-2010, 06:40 PM
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Yes.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 09-12-2010, 04:51 AM
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Jim,

Check out the wastegate circuit on this MODE (Holcombe) header. If you can't use two wastegates, then the next best thing would be to isolate the sides as far apart as possible. And notice the smooth transition off the collectors.

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Last edited by WinRice; 09-12-2010 at 07:13 AM.. Reason: Added text
Old 09-12-2010, 06:56 AM
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Many seem to think of the WG as just an add on or pressure release with little attention to making it flow as well as the header or muffler section.

With the modern turbos often running smaller hot sides for better boost response we seem to be calling on the WG to flow more and more.

If we can lower back pressure attributed to the WG circuit it to should help reduce reversion to at least some degree at the exhaust valves.

In a dream system we might even want to look at the tubing sizing of all three leg's about the WG circuit independently to better maintain exhaust velocity. Other wise when the WG is open the velocity after the WG branch can become greatly reduced (maybe cut in half in some cases). Then as flows hit the mouth of the turbo velocity will then have to be greatly accelerated (doubled or more in many cases).

Just a thought.

Old 09-12-2010, 10:13 AM
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