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External Wastegate Discussion

13K views 43 replies 8 participants last post by  paleyjim 
#1 ·
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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#2 · (Edited)
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.
 
#3 ·
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.
 
#4 ·
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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#5 ·
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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#6 ·
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
 
#12 ·
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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#13 ·
I love external gates with screamer pipes, :thumb:
 
#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.
 
#15 ·
nice, sorry i didnt get around to it like i said, sometimes life gets in the way....:whistle:
 
#17 ·
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...
 
#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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#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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#20 ·
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...
 
#21 ·
Yeah and stainless makes it even worse. Significantly more expansion and contraction to deal with.

I did some rework of the passenger side piece Wednesday night. Hoping for another test fit tonight. If things go smoothly it is possible I could start fitting the wastegate on Saturday.
 
#22 ·
I test fit the crossover again Friday night. The rework I did worked out well. I tacked everything in place extensively under the truck and then pulled it out and started sealing things up. Finished up the welding Saturday morning and had the crossover bolted in by noon.


I haven't put many miles on yet. The ultragauge seems to be showing that % load on the highway to be down by about 2%. There may be a little more power, but it is tough to tell. My butt dyno likes to lie, so I have pretty much ignore it.


I have a new shift cable to install tonight, but am hoping to start playing with wastegate fab tomorrow.
 
#23 ·
I made a little progress with the fabrication last night. I spent more time just looking at things than actually working, but I can share a couple photos.


The wastegate I'm using is from Precision Turbo and Engine. I found it on Amazon. It is a 39mm, dual port. It comes with weld flanges as well as an assortment of 5 springs to mix and match to adjust boost pressure. I'm planning to run it with the factory boost control system so I took out all of the springs. The spring side of the actuator will be vented to atmosphere (probably in the air filter housing) and the other port will get connected to the wastegate solenoid. If this plan doesn’t work, I can always add springs and boost reference it.


I made a couple of cuts and tacks in the stainless last night. The long diagonal cut is not correct yet. I purposely left a bunch of extra material so that I could work slowly to the final shape. I think I can probably finish this cut up tonight, but I won’t likely cut a hole in the crossover and weld it in place until Friday night or Saturday.
 

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#24 ·
I put some miles on the new crossover to get a better idea if it made much difference. Full throttle runs seem to be about the same, but there is better response at 1/2 to 3/4 throttle. I found this kind of odd. It seemed to me that any improvement at medium loads would also be there at high loads. But at any rate, the crossover was worth doing. So now on to the wastegate...


This ended up being some of the ugliest fabrication I've done in a long time. I forgot how to weld on thin stainless tubing and it took most of this project before I relearned the skill. Repairing burn through slowed me down a bunch.


Friday night I spent some time getting the wastegate pipe to mate nicely with the crossover. Then pulled the crossover out, cut the matching hole into it, and welded up the high pressure side.


Saturday I put the crossover back in and bolted the wastegate in place. I was going to call it quits at this point, but since I had pulled the springs out of the gate, there was nothing to hold it shut. I could have put the springs back in, but I decided to go ahead and run the vacuum lines and allow the vacuum system to hold it shut. Then things kind of snowballed on me... one thing led to another and I ended up finishing the install. I'll likely do a better job of installing the vacuum lines in the near future, but it works for now.


I had built a spring gate a while back, but didn't like it and took it back off. I grabbed it off the shelf, put it on, and cranked it down to keep the GM8 gate closed. Then went for a test drive with the outlet side of the wastegate wide open. What a riot! I was laughing out loud. I couldn't tell from the short drive if there was any power difference or not, but the noise of the gate was quite humorous. Not something I want to listen to all the time, but fun for a test drive.


I pulled it back into the shop to connect the outlet of the gate back into the exhaust. Very little drive time on it so far. Only to church and back this morning. There may be a very slight hiss from the gate that was not there before. I should know more once I get a chance to drive it harder. Boost control is exactly as it was with the internal gate - perhaps even more stable.


I'll report more once I get some miles on.
 

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#25 ·
are you running a drive pressure gauge?
 
#26 ·
No, but that would sure be nice info to have. Before and after.
Maybe something to consider doing before I swap turbos.
 
#27 ·
I hate to bump an old thread, but the idea of an external gate popped into my head tonight and I was glad to find a thread from this year at least. Did you hook the external gate up to the factory vacuum control system? I'd love to do an external gate and being able to hook it up to the factory vacuum system would be great.
 
#28 ·
The gate is connected to the factory boost control solenoid as I said I was planning in post 23. This "plan" did work out just fine. The spring side of the actuator is vented and the side that would normally be connected to boost is connected to the vac line from the solenoid. All springs were removed so that vac is the only thing holding the gate closed.
 
#30 ·
I lost my boost and set a boost related code a few days ago. Did not get a chance to troubleshoot it. I was suspecting possibly a frozen gate since it is fairly low in the system and water could collect there. A 10 minute drive home from town did not bring back my boost so I kind of ruled out the frozen gate. A 1/2 hour drive to pick up a friend yesterday DID bring my boost back to normal. So maybe the solenoid was frozen and the engine compartment had to warm enough to thaw it. Just thought I would share.
 
#31 · (Edited)
just thinking out loud here, could it possibly be that due to the placement of the gate that the exhaust is cooling off and depositing soot/carbon and jamming up the works? doesnt seem plausible it would be moisture, the exhaust is hot pretty much straight away, and would thaw it quickly would be my thinking...

have you thought of wrapping the pipe to retain more heat and more velocity?
 
#32 ·
It is possibly soot related, but I don't think so. It just seemed to act like something was frozen. You are right though that a frozen gate would thaw very quickly. The solenoid would take much longer. If it freezes up again I'll try to do some basic troubleshooting to get a better idea.

I have thought of wrapping the pipe. And plan to. Probably when the new turbo goes in. I'll need all the heat I can get to spin that thing up.
 
#33 ·
has this froze up again on you?
 
#34 ·
This morning was the first time I've started the truck since I reported the problem. It was frozen up again, but not as bad as before. I was still able to build 5 psi when I stepped into it.

If it is still acting up when I get home, I'll put a vac gauge in the line from the solenoid to see what I've got at that point.
 
#36 ·
Boost was low when I left work, but farting around in traffic brought it back to normal. Everything was normal when I got home, but I took a baseline vac reading from the solenoid anyway. Will throw the vac gauge in the truck so I can test when it acts up again.
 
#37 ·
Well, I can't say that my diagnostics re bulletproof here, but it looks like the low boost is due to a freezing up boost control solenoid (BCS). First photo shows the vacuum reading when everything was working normally a few days ago. Second shows the vac reading when boost was low this morning. Last photo shows the vac reading after a few minutes of a heat gun blowing on the BCS. Now I just need to figure out how to keep it from freezing up. I sprayed some WD40 into the BCS, and will see how that works out.
 

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#38 ·
The low boost problem seemed to be related to the cold at first, but after the temps warmed up some I was still having problems. Pulled the BCS and cleaned it a bit and it has been working consistently again. Looks like the external gate may be leaking a bit of soot into the vac line. I'll likely start cleaning it at every oil change. Or I may eliminate the vac system since I am nearly ready to run a much bigger turbo.
 
#40 ·
The new one arrived last night. :thumb:
 
#41 ·
most who run external gates, also run cheap clear fuel filters in line between the control and gates to catch some of the carbon particles....
 
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