External WG Incident Angle

[turboshad]

How important is the incident angle/placement on an external WG, or maybe better, how much will it really effect things. I see allot of WGs at 90deg to the exhaust flow but have read that the entrance flow should be as smooth as possible. I am working on my header design and have been able to get one WG at a decent angle and in the center of where the two runners meet but for the life of me I can't make the other one fit with much of an angle and it is more going off of the side of one of the runners. Should I keep pulling my hair out or am I fussing over peanuts?

[turbovanman²]

Two? I would say angles would be perfect but then, we have to make sacrifices to fit it all, so your fretting hairs, lol.

[turboshad]

Two?

Twin scroll.

[Force Fed Mopar]

Seems like if you make it flow too well into the wg, it might hurt flow into the turbo? Maybe not.

[turbovanman²]

Twin scroll.

Ahhhhh, schweet.

[zin]

I'd expect that while a nice smooth approach to the WG would improve its flow efficiency, depending on where and what angle it's installed at could create turbulence for the turbine, which would hurt performance more than an inefficiency on the WG side.

After all you could just put a bigger gate on if it wasn't keeping up.

Mike

[Ondonti]

Weld the middle of a bend in the bad spot instead of trying to get a "good" angle on the straight pipe. It will make for a larger hole but it will transition well You can run a 90 degree angle and have it flow much better then a 90 degree angle. Plus there will be no brick wall for exhaust to hit, just a sharp edge since the radius will have already started. 90 degree bend and almost completely hack off one leg parallel to the leg you are cutting. Will give you an oval and act just like you want it to when exhaust is flowing.

Usually the solution to crappy 90 degree setups is to run way more wastegate then you need. There must be consequences but I couldn't say what they are. Exhaust hitting the far side of a straight 90 wastegate must cause excess (more then needed) backpressure. I will also go with the idea that controlling boost or flow through the turbine should be concentrated on velocity and momentum. Possibilities of creating excess pressure would then need to be eliminated. Real world difference? Maybe inconsequential for some things, huge for others.

[Reaper1]

Ultimate set-up's like to the the flow to be biased to the wastegate for boost control. However, pressure differential will win every time, so I think you're splitting hairs, especially with your design.

You could divorce the WG from the header by a bit too, so you could achieve a better angle for the WG port off of the collector if it really means that much to you.

[turboshad]

Ya, I was going to use a bend for the "bad" placement one, it's just a pig to model with 3D sketches. The one that is close to 90deg is almost right on the plane of the firewall so there isn't much room. Where I have them is about the only place they would fit unless I started from scratch with the header design. I don't really want to do that which is why I was looking for some opinions on how critical or performance effecting it actually was. If it was a serious matter I would look a bit deeper into different runner placement to make things work better.

[Shadow]

While my experience with external W/G's is somewhat limited, this is what I've found. Running the W/G 90 deg off the header (or manifold) gives better upper boost control and allows for higher boost on less spring.

We had an SRT-4 that was running a header with the W/G 90 deg and it ran 30 psi without issue and could have held a lot more. (judging by how much duty we were using on the EBC) Swapped out the header for a W/G biased design and ran the same W/G and couldn't make more than 18psi boost on the same spring. Ordered a bunch of springs and had a hard time getting it back to where it was and it never made any more power than it did on the original 90 deg W/G header.

This is where I was left scratching my head after trying to digest what Aarron was saying last year about W/G biased set-ups taken to the max. It makes sense that IF the W/G is being biased, as the PR rises you Should get more flow through the W/G so more HP, but the amount of spring you would need might make street tune hard to dial in at lower boost. (would have been nice to know what PR you need to reach in order to see the benefit?) Now with an external you can just switch springs, but with the Holset can, I can't.

I took a good look at the W/G on the holset and it is the opposite of biased, it actually has a slight hump in front of it to direct the flow over the hole and into the turbine. I have not touched the W/G hole on the Holset and it holds boost rock solid from 18 to 37 psi so far. I've been toying with the idea of porting and biasing the W/G to the flow of the housing, but I'm afraid that the extra pressure acting on the W/G might effect my ability to hold boost to 40 psi?

So what does my rambling on have to do with the Q at hand? I would think that one W/G biased and one running 90 deg you would need two different springs in order to keep the W/G's equil at any constant boost level. Otherwise the biased W/G will always be a little more open and trying to run slightly less boost than the 90 deg one. That or run a slightly larger W/G on the 90 deg to equil the flow.

Only way I can think of knowing for sure would be two seperate pressure taps to measure each side. Is this splitting hairs and could the difference possibly be enough to warrant the effort? Don't know, but it would be interesting to see what the difference is

[roachjuice]

While my experience with external W/G's is somewhat limited, this is what I've found. Running the W/G 90 deg off the header (or manifold) gives better upper boost control and allows for higher boost on less spring.

We had an SRT-4 that was running a header with the W/G 90 deg and it ran 30 psi without issue and could have held a lot more. (judging by how much duty we were using on the EBC) Swapped out the header for a W/G biased design and ran the same W/G and couldn't make more than 18psi boost on the same spring. Ordered a bunch of springs and had a hard time getting it back to where it was and it never made any more power than it did on the original 90 deg W/G header.

This is where I was left scratching my head after trying to digest what Aarron was saying last year about W/G biased set-ups taken to the max. It makes sense that IF the W/G is being biased, as the PR rises you Should get more flow through the W/G so more HP, but the amount of spring you would need might make street tune hard to dial in at lower boost. (would have been nice to know what PR you need to reach in order to see the benefit?) Now with an external you can just switch springs, but with the Holset can, I can't.

I took a good look at the W/G on the holset and it is the opposite of biased, it actually has a slight hump in front of it to direct the flow over the hole and into the turbine. I have not touched the W/G hole on the Holset and it holds boost rock solid from 18 to 37 psi so far. I've been toying with the idea of porting and biasing the W/G to the flow of the housing, but I'm afraid that the extra pressure acting on the W/G might effect my ability to hold boost to 40 psi?

So what does my rambling on have to do with the Q at hand? I would think that one W/G biased and one running 90 deg you would need two different springs in order to keep the W/G's equil at any constant boost level. Otherwise the biased W/G will always be a little more open and trying to run slightly less boost than the 90 deg one. That or run a slightly larger W/G on the 90 deg to equil the flow.

Only way I can think of knowing for sure would be two seperate pressure taps to measure each side. Is this splitting hairs and could the difference possibly be enough to warrant the effort? Don't know, but it would be interesting to see what the difference is

You run an internal wg on your holset setup? What can are you using?

[Shadow]

The factory Holset can that came with it. Should be good to at least 58psi boost.

[Reaper1]

For a WG biased set-up you would want to run a smaller WG anyway due to having the problem Rob described. You NEED more flow capacity on something that is flow hindered to begin with, but with something that is designed to flow you don't. Plus, if you are wanting to run higher boost numbers, then you don't need to flow as much through the WG anyway, so this is why most of the time you see "race" gates being a smaller size than "street" gates.

[Ondonti]

Or you can build it right and learn how to control boost. C02 to the wastegate port is how the educated class would solve the problem. That or improve the pre downpipe side to decrease backpressure (which is what forces open the wastegate). Increasing backpressure with a bad wastegate will get you more boost but that is just dumb. No other way to say it. Everytime I have seen someone diagnosing a lack of ability to build boost, they are always doing something wrong or misunderstanding how their turbo system functions on a 4 stroke motor. Even people with $50k+ builds.

That radius is gonna be fine and I don't consider it a 90 degee when you build it like that. I never really got extruding curved shapes when I took a Pro E class. Got it to work a few times for an assignment and then never touched the stuff again.

Running a small 38mm has not helped me ever create extra boost. All you can get is boost creep and I am too tired to flame that intelligent pathway.

[Vigo]

I am interested in the problem Shadow is describing. Seems that you would HAVE to run two pressure taps to ever truly know if it was happening or not, otherwise you may have symptoms and no good way to diagnose them.

I think the setup you are building looks fine, but i am with shadow on including two pressure taps in the build before it goes into the car, even if you dont hook up to them right away. Just seems like good planning to keep you from running into a diagnostic can of worms if there IS a problem with uneven wastegate action down the road.