exhaust flow with shimmed wastegate
11-06-2007, 07:33 PM
#1
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Thread Starter
exhaust flow with shimmed wastegate
I know when you shim the wastegate, the idea is to have more pressure needed to open the wastegate.
But ,it seems to me the wastegate valve will also open less off its seat by the amount equal to thickness of the shims. Am I seein' this right? Wouldn't that hinder exhaust flow through the wastegate, possibly causing boost creep?
Isn't there some sort of formula around that states that a valve will continue to flow more with more lift, with diminishing returns, up to a certain point?
But ,it seems to me the wastegate valve will also open less off its seat by the amount equal to thickness of the shims. Am I seein' this right? Wouldn't that hinder exhaust flow through the wastegate, possibly causing boost creep?
Isn't there some sort of formula around that states that a valve will continue to flow more with more lift, with diminishing returns, up to a certain point?
11-07-2007, 03:49 AM
#2
Racer
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You're right, thats why you are only supposed to put in a shim or two. With a stock K26 on my car and one shim, I didn't have problems with boost creep. I think the shim idea is fine for the stock turbo, but wouldn't do it for a larger one that flows more.
11-07-2007, 09:58 AM
#3
You are not going to get boost creep from that valve - its large.
I use a Tial 38 and I am JUUUUUST starting to come up a tiny bit at 6-7000 RPM using a real 780 HP turbocharger (with an exhaust configuration that will actually support it also).
And I believe, that the factory 951 valve is slightly larger than the Tial.
So you shouldn't have to worry about boost creep with a 300 hp turbo.
And when I say "shouldn't", I am being diplomatic - that wastegate will be big enough at 50 thousandths lift.
I use a Tial 38 and I am JUUUUUST starting to come up a tiny bit at 6-7000 RPM using a real 780 HP turbocharger (with an exhaust configuration that will actually support it also).
And I believe, that the factory 951 valve is slightly larger than the Tial.
So you shouldn't have to worry about boost creep with a 300 hp turbo.
And when I say "shouldn't", I am being diplomatic - that wastegate will be big enough at 50 thousandths lift.
11-07-2007, 11:08 AM
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11-07-2007, 10:43 PM
#5
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Well ST;
I probably have the same turbo as you and it's on a 3 liter, and I am getting boost creep.
So, update:
I took the wastegate off and did some research.
I think my wastegate is shimmed too much.
By the way, it's a 38 mm valve, just like the tial.
At fully open the lift is 8 mm; not enough.
I will reduce shims to produce a 11 mm lift, which is slightly more than the 25% of valve size.
If that doesn't work I'm looking into a larger wastegate.
By the way, the consenus is that when running high boost, one can get away with running a smallish wastegate, because more exhaust needs to go through the turbine, not the wastegate. But, I'm thinking: with higher boost comes also more exhaust mass (flow, energy, volume). So, even if more exhaust has to go through the turbine (to produce the boost in the first place), there is also more waste gases in the system.
Anybody know more about this?
I probably have the same turbo as you and it's on a 3 liter, and I am getting boost creep.
So, update:
I took the wastegate off and did some research.
I think my wastegate is shimmed too much.
By the way, it's a 38 mm valve, just like the tial.
At fully open the lift is 8 mm; not enough.
I will reduce shims to produce a 11 mm lift, which is slightly more than the 25% of valve size.
If that doesn't work I'm looking into a larger wastegate.
By the way, the consenus is that when running high boost, one can get away with running a smallish wastegate, because more exhaust needs to go through the turbine, not the wastegate. But, I'm thinking: with higher boost comes also more exhaust mass (flow, energy, volume). So, even if more exhaust has to go through the turbine (to produce the boost in the first place), there is also more waste gases in the system.
Anybody know more about this?
11-09-2007, 06:06 AM
#6
Nordschleife Master
By the way, the consenus is that when running high boost, one can get away with running a smallish wastegate, because more exhaust needs to go through the turbine, not the wastegate. But, I'm thinking: with higher boost comes also more exhaust mass (flow, energy, volume). So, even if more exhaust has to go through the turbine (to produce the boost in the first place), there is also more waste gases in the system.
Anybody know more about this?
Anybody know more about this?
Your case with a 3 liter turbo and low boost is the perfect example of a system that needs a larger wastegate.
I've seen boost creep and spikes on a 3l with Tial 38mm on low boost (sub 1.0 bar).
11-09-2007, 06:44 AM
#7
Well ST;
I probably have the same turbo as you and it's on a 3 liter, and I am getting boost creep.
So, update:
I took the wastegate off and did some research.
I think my wastegate is shimmed too much.
By the way, it's a 38 mm valve, just like the tial.
At fully open the lift is 8 mm; not enough.
I will reduce shims to produce a 11 mm lift, which is slightly more than the 25% of valve size.
If that doesn't work I'm looking into a larger wastegate.
By the way, the consenus is that when running high boost, one can get away with running a smallish wastegate, because more exhaust needs to go through the turbine, not the wastegate. But, I'm thinking: with higher boost comes also more exhaust mass (flow, energy, volume). So, even if more exhaust has to go through the turbine (to produce the boost in the first place), there is also more waste gases in the system.
Anybody know more about this?
I probably have the same turbo as you and it's on a 3 liter, and I am getting boost creep.
So, update:
I took the wastegate off and did some research.
I think my wastegate is shimmed too much.
By the way, it's a 38 mm valve, just like the tial.
At fully open the lift is 8 mm; not enough.
I will reduce shims to produce a 11 mm lift, which is slightly more than the 25% of valve size.
If that doesn't work I'm looking into a larger wastegate.
By the way, the consenus is that when running high boost, one can get away with running a smallish wastegate, because more exhaust needs to go through the turbine, not the wastegate. But, I'm thinking: with higher boost comes also more exhaust mass (flow, energy, volume). So, even if more exhaust has to go through the turbine (to produce the boost in the first place), there is also more waste gases in the system.
Anybody know more about this?
If ,on the other hand, you have a hybrid turbo from one of the suppliers on this list, it is possible that you have creep.
Tell me which turbocharger you have, and I will tell you the problem.
I know about the concensus of small wastegate/large turbo on this list - I wrote it.
At any rate you must get rid of that terrible wastegate.
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11-09-2007, 01:48 PM
#9
Rennlist Member
Thread Starter
Duke;
thanks for your explanation.
I'm going to be running 1.2 - 1.3 bar, so we'll see.
ST;
John's stage five
terrible wastegate?
There's nothing wrong with a NEW stock wastegate. It seems like the issue, when it comes to boost creep, is the valve size. If I went with a new tial 38 or a new lindsey unit, I wouldn't be solving my problem.
thanks for your explanation.
I'm going to be running 1.2 - 1.3 bar, so we'll see.
ST;
John's stage five
terrible wastegate?
There's nothing wrong with a NEW stock wastegate. It seems like the issue, when it comes to boost creep, is the valve size. If I went with a new tial 38 or a new lindsey unit, I wouldn't be solving my problem.
