First, here are the specs on my setup:
-5.3l with an LS1 cam
-2" hot side with truck manifolds
-VSRacing GT45 with a 44mm gate welded to the turbine housing
-4" exhaust with a cherry bomb that dumps in front of rear axle

Because of the tight space in the engine bay of my s10, I decided to place the wastegate directly on the turbine housing(got the idea from Sloppy Mechanics).

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Unfortunately, I have zero control over boost with this setup. I verified that all the plumbing is correct, the wastegate works correctly on the bench, and I even pulled the wastegate spring as a last ditch effort. The trend below was taken without a wastegate spring installed.

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My first thought was to do like Denmah did, and just add another 44mm wastegate. so I have one on the way. But then I thought maybe it would be better to install a larger gate that is placed a little more tangentially with the turbo, so I ordered a 50mm gate as well, haha.

Anybody got any thoughts on what might be best? Right now I'm leaning heavily towards the 50mm gate with the better placement. It'll look better than two gates, and my gut feeling tells me it will work better, but this is my first attempt at anything turbo, so I have zero experience.

 

I personally would do whatever is easiest. No problems with 2 gates, but if its just as easy to do a single, and you like it better, then there's your answer. A 50mm with good placement should easily keep boost in check.

May be a dumb question, but does the valve moves freely on the 44mm?

 

The 50 will be slightly more work, but not much more. I've got to attach a new vband to the turbine and merge back into the exhaust either way.

The valve does move freely, I hooked it up to shop air and it cracked around 5-6psi, and was fully open by 8.

The advice is much appreciated, makes me feel a more confident that I'll get this issue cured.

 

Can you hang the gate wide open. If you cant control boost then its too small. That gate may not control 5 psi. But it may control 10-15 psi.

 

I pulled the spring out of the wastegate and it still made 12psi. The only thing that stopped it from climbing higher was the fact that I haven't worked on the tune above that point, and it's pig rich up there. I want to be able to control pretty low boost, I'm pretty sure traction is going to be a problem. Granted, this thing takes forever to build boost, so if it could hold it to 15 it would probably be fine.

I thought the 44mm gate is pretty standard for a 5.3 with a 69mm GT45, so I'm guessing my placement is just piss poor. I'm going to upgrade both size and placement for piece of mind.

 

A buddy of mine put the wastegate on the turbo as you've done, however he had it angled so the exhaust had a straight shot at the valve, right before the radius began. I believe the placement here is the key, as exhaust velocity tends to ignore right angle pipes.

 

Its fixed!

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It's working a little too well now, it's holding it at a rock steady 3psi. I am setup with a boost solenoid with pressure referenced before the intercooler, and the 50mm is probably a little big, so 3psi on spring alone probably isn't that bad. I'll just have to start tuning the solenoid duty tables.

Here's what I ended up with.

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On a side note, the spool time has improved greatly. I can't imagine how the waste gate solved that, so I must have fixed an exhaust leak somewhere.

Thanks for all the help!

 

Back psi is? I doubt that muffler is helping much.

 

Not sure, I've been meaning to hook something up, I've got an extra analog in wired to the engine bay. I would hope it isn't too bad at only 8psi with a 4" exhuast. The muffler is a Cherry Bomb, it's not much more than a 4" perforated pipe, covered in a handful of fiberglass, haha!

Are you thinking back pressure is the reason the first setup didn't work?

 

Not so sure about the muff, but the angle on the WG was a major contributor.

 

The amount of boost has nothing to do with the wastegate size.

The hot side pressure and the ratio of the waste gate valve area restriction to the turbine restriction, as well as the placement, is what causes problems. The gate has to be able to vent the exhaust off a lot faster than the exhaust flow through the turbine. A pretty large portion of exhaust flow has to be able to go out the gate, otherwise it has limited or no turbine speed control.

Anything that adds restriction to the wastegate's bleed path to open air makes it worse, because it reduces gate flow. That would include dumping it back into an exhaust pipe that has back pressure.

Not only is the location poor, because the exhaust is busy going in towards the turbine wheel, but then the gate has to dump the exhaust it does get through a bunch of back pressure.

The gate can be put on a pipe Y'ed off the hot side. It doesn't matter much which end of the pipe it is on. Early on I didn't have room to put my gate at a good spot up near the turbo flange so I dropped a pipe down and hung it on the end of that pipe. I rebuilt all that now, but it works the same as it did hanging on the pipe off my merge.

 

Tom, i'm not sure I understand, or agree with your first statement.... The gate has a lot to do with boost level.... equally important is the placement, but a small gate with perfect placement will still creep on certain applications. Low boost levels require a larger gate (more flow at typically lower pressures) whereas higher boost levels can get by with a smaller gate (less flow, and typically higher pressures, and larger differentials).

 

Let's look at how a waste gate works.

The available engine air pressure and volume is determined by how fast the compressor spins. We have to get it a target speed to make a certain boost at a certain flow. We do that speed control by either having engine exhaust run through the turbine or the wastegate.

It is the amount of exhaust volume we force through the turbine that determines speed. The wastegate is not regulating compressor pressure directly, it is diverting exhaust. It has to be sized and placed to be able to divert enough exhaust to slow the turbine. It isn't sized by if I want to run 30 psi or 3 psi, it is sized by the exhaust flow rate and the exhaust hot side pressure, and how much back pressure the turbine and exhaust pipes have. It is sized by horsepower and hot side pressure and turbine and exhaust back pressure, not boost.

 

That makes my head hurt...lol. The bottom line is you need enough gate flow to moderate the turbine speed to maintain your boost goal, whether you choose the gate by hp, or some other method the fact remains that a gate that is too small for the combo (even placed right) will not allow you to control boost as low as you want. We may have to agree to disagree on this as I don't understand the point you're trying to make.

 

I'll agree that a restriction on the outlet of the wastegate is a bad thing, but I'm kind of conflicted as to whether dumping it back into the exhaust will affect its ability to control boost. The lower pressure differential across the valve caused by high back pressure should restrict the flow rate through it, but if the turbine sees the same pressure differential, I would think its flow rate would decrease in proportion to the wastegate.

I doesn't appear that the location was the problem with the first setup, just the orientation. After I changed it, it was able to hold the boost at a rock steady 3psi.

I kind of worked myself into a corner with the hot side piping. I could have run dual gates pretty easy if I just dumped them straight to atmosphere, but I really wanted to dump it back into the exhaust (going for the sleeper thing on this one) and there was no good path to get from the merge to the exhaust.

It's not volume of gas alone that moves the turbine(1000 cubic feet in an hour won't do much, 1000 cubic feet in a minute probably will), its the rate of flow through it that does. But I think that's what you meant.

I'm not sure why you say that boost pressure has nothing to do with selecting wastegate size. Yes, the purpose of the wastegate is to divert exhaust gas away from the turbine. And we need to now how much exhaust gas we have total, and the amount that needs to flow through the turbine to determine how much to divert. But the end variable that we are trying to control is boost, and therefore all those other variables hinge on boost.