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In the near future, I’m planning to build a 2.5” crossover to replace the original. Further down the road, I’ll be installing a BW S300 non-gated turbo. The S300 that I have is big enough that I probably don’t need to worry about controlling boost – at least until I add more fuel – but I was still thinking that a wastegate might be nice to have in the system.

I was thinking of adding an external wastegate at the crossover since there is enough space to do it, I’m fabricating the crossover anyway, and dumping the exhaust from the crossover reduces the amount of exhaust flow through the restrictive passenger side manifold.

Which got me thinking and brings me to my question: I wonder if there is any benefit to installing an external wastegate with the original turbo? If I were to hold the GM5 internal wastegate closed and dump the extra exhaust flow from the crossover via an external wastegate would there be any efficiency gained? The only flow through the manifold would be what is actually being used to spool the turbo.

What do you all think? Is there any reason not to give this a try when I build the crossover?

What size is the wastegate valve in the GM turbos? Should I stick with the same size? Larger?
 

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Also wondered this myself, :popcorn: I would think you'd maybe want the wastegate closer to the turbo but that's hard to do with the stock manifold. But i'm unsure.
 

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I think someone did put an external gate in the X crossover, it will work but it might need some fine tuning due to only venting 4 cylinders.

The ex gate might help a stocker and I could be wrong, but most of the problem with the stocker is simply size, its just too small.
 

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if the gate is installed into an adapter at the base on turbine housing, it will vent all the back pressure into the exhaust, so, with a gm-x turbo it will completely by-pass the back-up in the turbine into the downpipe, in a manner increasing the size of the turbine housing by reducing the gases passing through it.....
 
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if the gate is installed into an adapter at the base on turbine housing, it will vent all the back pressure into the exhaust, so, with a gm-x turbo it will completely by-pass the back-up in the turbine into the downpipe, in a manner increasing the size of the turbine housing by reducing the gases passing through it.....
you could do something like this, or drill a hole in the side face of exhaust manifold facing the front and mount the gate there....
 

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respect the DB4 5722....
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In the near future, I’m planning to build a 2.5” crossover to replace the original. Further down the road, I’ll be installing a BW S300 non-gated turbo. The S300 that I have is big enough that I probably don’t need to worry about controlling boost – at least until I add more fuel – but I was still thinking that a wastegate might be nice to have in the system.

I was thinking of adding an external wastegate at the crossover since there is enough space to do it, I’m fabricating the crossover anyway, and dumping the exhaust from the crossover reduces the amount of exhaust flow through the restrictive passenger side manifold.

Which got me thinking and brings me to my question: I wonder if there is any benefit to installing an external wastegate with the original turbo? If I were to hold the GM5 internal wastegate closed and dump the extra exhaust flow from the crossover via an external wastegate would there be any efficiency gained? The only flow through the manifold would be what is actually being used to spool the turbo.

What do you all think? Is there any reason not to give this a try when I build the crossover?

What size is the wastegate valve in the GM turbos? Should I stick with the same size? Larger?
today i will measure the flapper size to put here.... also from the searching we have done, the smallest size we could find was a 38mm, which is pictured, although we did not go into the uber high priced ones, just stuck with the cheepo china ones....:confuzeld
 

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you could do something like this, or drill a hole in the side face of exhaust manifold facing the front and mount the gate there....

That's what Turbonetics did back in the day. I bought a turbine housing for my Caravan with that done, then I did it to my GT35R, saves hacking up manifolds etc but it does ruin a turbine housing if you need to sell it and someone doesn't want that.



 

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That's what Turbonetics did back in the day. I bought a turbine housing for my Caravan with that done, then I did it to my GT35R, saves hacking up manifolds etc but it does ruin a turbine housing if you need to sell it and someone doesn't want that.




The one in the pics of the compounds, is not in the turbine housing, it is a flange spacer with the dump tube coming off of it. T3 to T3.....
 
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The one in the pics of the compounds, is not in the turbine housing, it is a flange spacer with the dump tube coming off of it. T3 to T3.....
I looked at those, no room on my Mini, :bawl:

On a side tracking note, when will your new setup be ready?
 
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I looked at those, no room on my Mini, :bawl:

On a side tracking note, when will your new setup be ready?
next winter for another compounds build, center mount is already done, just waiting for time to swap engines, and while the engine is out, to finish the firewall mod off, and GTmat everything.... also got twins brewing here right now, but not ready to post anything about them, and not in jims thread for sure, sorry for the derail jim....:Insane:
 

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Discussion Starter #11
sorry for the derail jim....:Insane:
No worries! Its all good!

I was hoping to get started on this in the next week or so, but my wife has pointed out that I have higher priorities right now. The washing machine is acting up and the A/C quit in the Subaru. We got a taste of warm weather last week and the A/C suddenly jumped up the list.
 

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I need one too.
Running up to 20psi of boost now when I go back down closer to sea level and I plan on turning up the fuel. If I don't put a waste gate on I have a feeling things are going to break.
I would like one of those external ones more or less identical to the ones youall pictured and exit the WG pipe by the front passenger wheel arch. That way it can dump when I go to pass a prius or something slow.
 
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I love external gates with screamer pipes, :thumb:
 

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Discussion Starter #14
I recently put a GM-8 on my truck and pulled apart the GM-5. To answer my own question, I measured the wastegate port in my GM-5 and it was 1.25" or about 32mm.
 

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I recently put a GM-8 on my truck and pulled apart the GM-5. To answer my own question, I measured the wastegate port in my GM-5 and it was 1.25" or about 32mm.
nice, sorry i didnt get around to it like i said, sometimes life gets in the way....:whistle:
 

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Discussion Starter #16
nice, sorry i didnt get around to it like i said, sometimes life gets in the way....:whistle:
No worries!
I've started shopping around for an external gate. Not sure I want to pay for a tial just for experimentation, but also not sure I trust a $30 pos. Trying to find some middle ground.
 

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external gates dont really do much, other than gate, or make noise if just vented into the atmo, in our experience with mechanical pumps, and on demand in-cab adjustment, they produce smoke, when used with a single turbo, tried it with big turbos, and small ones, the place it shines thru is for spooling a primary harder in compounds...
 

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Discussion Starter #18
Update

I've been working slowly on crossover fabrication. Hoping to make some more progress this week. I also picked up an external gate to mess around with. Will be interesting to see what we can learn.


I plan to test with just the crossover first to see if I pick up any power. Then I'll disable the factory gate and set up the external.


Here's a photo of how the crossover is sitting right now. I need to bolt it in place, make sure everything lines up ok, then finish welding it.
 

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Discussion Starter #19
Initial Test Fit

Well the test fit didn't go as well as I had hoped. Not surprising since the fab was done by eye off an old mangled crossover.
I couldn't get the whole assembly to bolt up properly, so I ended up taking the flex section off and bolting the 2 sides up individually. I need to do some more cutting and welding on the passenger side to get it pointed directly at the drivers side.


Some photos...
 

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good progress, sectioning and welding is always tedious work, but keep at it and it will come.... once you get your general roughing done, might be a good idea to stand the cross over up and tack it to a steel table, or something rigid, like a piece of 6" wide heavy channel so it keeps the heat tweak to a minimum...
 
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