External wastegate Q

[czy18e]

Hi,

I'm running a tial 38mm wastegate on gcg manifold with no boost control and a 12psi spring.It is venting straight to atmosphere with no pipe on it.

I'm getting boost creep the higher the gear and the higher the revs the more the boost goes up.

My mechanic reckons its cos my turbo is too small(,63 exhaust on t3/t4)and my system is so efficient that the little turbo just keeps boosting and if i had a bigger turbo with bigger exhaust side it would be able to control boost alot easier.

Now before any of you laugh it off i am on full gate 12psi with 15 degrees timing before 3500 rpm.less lag than my gf's stock 33 without really trying.

The car is light and has a very efficient inlet and exhaust tract,But i wanted a second opinion can anyone shed any light on this ?

I want to go gt series turbo early next year anyway but i want to know i'll have stable boost before i slap on a gt 35 or something.

Cheers.

[dnb]

id say he is spot on mate.got any pics of the manifold?

[czy18e]

Cool thanks dude,

Go to gcg website for photo i dont have a camera.

[Sydneykid]

Hi,

I'm running a tial 38mm wastegate on gcg manifold with no boost control and a 12psi spring.It is venting straight to atmosphere with no pipe on it.

I'm getting boost creep the higher the gear and the higher the revs the more the boost goes up.

My mechanic reckons its cos my turbo is too small(,63 exhaust on t3/t4)and my system is so efficient that the little turbo just keeps boosting and if i had a bigger turbo with bigger exhaust side it would be able to control boost alot easier.

Now before any of you laugh it off i am on full gate 12psi with 15 degrees timing before 3500 rpm.less lag than my gf's stock 33 without really trying.

The car is light and has a very efficient inlet and exhaust tract,But i wanted a second opinion can anyone shed any light on this ?

I want to go gt series turbo early next year anyway but i want to know i'll have stable boost before i slap on a gt 35 or something.

Cheers.

Does not sound right to me. If the turbo is too small the compressor won't be able to supply enough airflow to hold the boost up as the rpm increases) If the turbo is too small the turbine won't be able to flow enough exhaust as the rpm increases and the engine will gradually choke itself. Exhaust back pressure builds

up to such an extent that it matches the boost and the power drops.

I reckon the wastegate is too small to bypass enough exhaust gas. So it keeps flowing to the turbine and building boost even when the wastegate is fully open.

So I suggest you try this formula for calculating wastegate sizes from a previous post........

Save time doing a search, here is the abreviated version.....

I have pretty good success using this formula to determine external wastegate sizes;

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor

So let's apply it to your car;

300 rwkw = 480 bhp

480 bhp = 44 lbs of airflow = 44 mm wastegate

Now if you want to run 19 psi, then that's the right size wastegate.

But we need to apply the boost correction....

My experience indicates that to get 300 rwkw out of a GT3040 you would need to run around 1.5 bar (22psi). So using the formula...

44 / 22 X 19 = 38 mm.

For those who haven't read the thread..............

http://www.skylinesaustralia.com/fo...ead.php?t=43638

Hope that helps :uh-huh:

[cameron]

SK,

Link doesnt work :uhh:

[dnb]

what if the gate pipe is not able to flow enough at full revs in high gears. there is more gasflow,so if the gate pipe leavs the manifold at an awkward angle(my reason for asking for pics of it) possibly the gasses dont want to flow down the pipe to the gate

this might work

http://www.gcg.com.au/default_800x600.htm

[japsky33]

Dnb your sort of correct that was an issue with the car the bend off the gate was to tight, I told him this he removed it but its still creeping (just not as bad) I thought I would let this post go for a bit and once again Sydneykid with his formula's .

There is no exhaust back pressure issue here. ITS SIMPLE.

THe manifold is designed correctly taking exhaust pressure for the wastegate from every cylinder the dump pipe is over 3inchs so what then ? well theres to much exhaust velocity and to small a wastegate to control the turbo from creating more boost then his set level in this situation Case closed, Either modify or upgrade turbo, OR add an extra wastegate.

czy18e I think you worded that wrong and infact what you was saying the mechanic said is exactly what SydneyKid said.

300rwkw needing 22psi with a 3040 ? Well today I got 355rwkw with 20psi on a standard 25 with a 3040!!.

I dont understand how you are using HP readings to indicate wastegate sizes its beyond me ? Do drift cars often use twin 38ml ex gates becuase there making 800rwkw ? NO its to control boost on a very efficent manifold and small turbo for quick responsive HP. That formula should be worked out on exhaust velocity and the turbos A/R both front and back.

BR,

JH

[czy18e]

The pipe diameter on a gcg manifold is 38mm so slapping a 45mm wastegate on wouldnt help would it??

I havnt heard anyone else complain about there product??

[Sydneykid]

300rwkw needing 22psi with a 3040 ? Well today I got 355rwkw with 20psi on a standard 25 with a 3040!!.

What spec 3040? What other mods? How accurate is the dyno? Was it hub or roller? It was an example of the calculation, not a chest beating exercise, DOH!

I dont understand how you are using HP readings to indicate wastegate sizes its beyond me ?

If you read it properly you will note that I use the bhp to calculate the airflow in lbs per minute. Remember it's a rule of thumb calculation, if they know their target BHP then anybody can use it. It was posted so the guys on here could have some place to start. At the same time kill the myth that bigger is always better when it comes to wastegates.

That formula should be worked out on exhaust velocity and the turbos A/R both front and back.

So what formula do you use? Please give some real world examples. I used 40 cars, all from this forum to verify that formula.

Do drift cars often use twin 38ml ex gates because there making 800rwkw ? NO its to control boost on a very efficent manifold and small turbo for quick responsive HP.

Well, I have seen, maybe 100 drift cars, and I can't remember seeing 1 with twin wastegates. Unless you mean twin turbo internaly wastegated, I have seen a lot of those. But they don't win anything.

I can see you and I are going to have some interesting posts

[japsky33]

HI SydneyKid I didn understand this last bit ? I can see you and I are going to have some interesting posts :cheers ??

What spec 3040? What other mods? How accurate is the dyno? Was it hub or roller? It was an example of the calculation, not a chest beating exercise, DOH!

The dyno would be as accurate as any other, roller dyno. I only put that in there mucking around it was not a chest beating excerise either. Though it is the truth.

Standard 3040 with .82 rear housing.Tial 48ml gate. My MPH speaks for its self 127Mph standard road tyres.

If you read it properly you will note that I use the bhp to calculate the airflow in lbs per minute. Remember it's a rule of thumb calculation, if they know their target BHP then anybody can use it. It was posted so the guys on here could have some place to start. At the same time kill the myth that bigger is always better when it comes to wastegates.

So what formula do you use? Please give some real world examples. I used 40 cars, all from this forum to verify that formula.

I did read it correctly and I still dont see how HP is going to help you calculate i think its a hit and miss formula if you ask me, When the factoring matter here is efficency on the exhaust side Manifold/exhaust velocity/wastegate positioning in relation to what cylinders it is venting if not all ( Yes I have seen some bodgy manifolds ) also in relation to the size of the turbo on what motor you are using it on I think this formula might have proven reliable to you used on RB25's ?. For example a car I tuned a few weeks ago Toyota Soarer with some bodgy manifold on it 48ml turbosmart gate 1.12 rear housing and this thing would not control the boost, any ideas why ?

I have not used a formula I have just been accurate enough with my choice of wastegates and yes I do go for the larger wastegate one for expansion of my mods (and customers) and also for tighter control on higher boost applications.

Well, I have seen, maybe 100 drift cars, and I can't remember seeing 1 with twin wastegates. Unless you mean twin turbo internaly wastegated, I have seen a lot of those. But they don't win anything.

Australian Drift Cars there all usually internal gated and no I'm not talking about twin turbo's internally gated you think Im an idiot ? IM talking about jap D1 Style cars.

[japsky33]

The pipe diameter on a gcg manifold is 38mm so slapping a 45mm wastegate on wouldnt help would it??

I havnt heard anyone else complain about there product??

Not unless you expend the exit hole, Its not a complaint about there product its working fine. Your missing the point.

BR,

JH

[Sydneykid]

I have not used a formula I have just been accurate enough with my choice of wastegates and yes I do go for the larger wastegate one for expansion of my mods (and customers) and also for tighter control on higher boost applications.

So you guessed :wizard:

Australian Drift Cars there all usually internal gated and no I'm not talking about twin turbo's internally gated you think Im an idiot ? IM talking about jap D1 Style cars.

OK, I believe you, just give me 5 X D1 cars that run twin wastegates. For every 1 you name I will give you 10 that run a single. Let's go........... :Pimp2:

[japsky33]

I didnt guess I use my own formula based on the facts not air fairy airflow becuase of how much boost I want to run, Hell the customer might want to run 10 one day then 30 the next I dont know do you ?

OK you believe my but now we have to play a stupid game of i know one well i know 10!!!... come on SydneyKid ? Give me answers to your formula that I'm asking not stupid things like that. I'm only putting my two bits in to see if you can prove to me this formula for wastegate sizes.

BR,

JH

So you guessed :wizard: 

 

OK, I believe you, just give me 5 X D1 cars that run twin wastegates.  For every 1 you name I will give you 10 that run a single.  Let's go........... :Pimp2:

[Sydneykid]

OK lets start off with the theoretical stuff, posted some time ago.......

1. The wastegate size is relevant to how much horsepower you are targeting

2. If you want to run high boost, then a smaller wastegate is better than a larger wastegate. The idea being that in order to generate high boost you need most of the exhaust gas going through the turbine, not through the wastegate.

3. If you want to run low boost then a larger wastegate is better than a smaller wastegate. The idea being that in order to keep the boost low you need a lot of the exhaust gas going through the wastegate not through the turbine.

But what is high boost? Well for the sake of this discussion I have settled on 1.2 to 1.4 bar (18 to 21 psi) as being the divider, thus 1. 2 bar and under is low and 1.4 bar and above is high. How did I arrive at this number? Well based on the results of the surveys, this seems to be the most common point where the wastegate sizes change from theory 2 to theory 3 (above).

The next bit of theory is that it takes 1 lb per minute of airflow to make 11 bhp in a current generation 4 valve engine. This is a pretty well established piece of turbo sizing philosophy. But how do we relate this to wastegate sizing? Well referring to the results of the surveys, it seems a straight 1 to 1 relationship is not too far from the average, so 1 lb of airflow = 1 mm of wastegate diameter.

What I am trying to do with the formula is give a baseline, something to think about. An 85% fit type of thing. At the moment there seems to be a majority of guys wanting external wastegates who don't even know where to start. They have been told for big horsepower you need a big wastegate, which is not necessarily true. They have been told you can't have too big a wastegate, which is definitely not true. They have been told for high boost you need a big wastegate, which again is not necessarily true.

In order to do this there is one main assumption, that the turbo is pretty much the optimium size for the target power and boost. If it is totally wrong then whether the wastegate is sized correctly or not is really irrelevant. The turbo / engine mismatch is gunna kill horsepower / response anyway.

A a 50mm wastegate valve is going to weigh twice as much as a 35 mm one. So there is an inertia issue to be considered. I think that is really the crux of the problem. The diaphram has to move twice as much weight, in and out very rapidly. This has 2 undersirable effects incomparison to a smaller (more correctly) sized wastegate.

Firstly the too large a wastegate has to open and close more often, as it has too little exhaust flow when closed and too much exhaust flow when open. This wears the diaphram, due to the requirement for more movements and more weight.

Secondly all this opening and closing of the wastegate affects the amount of exhaust flow though the turbine, this leads to fluctuations in the boost control. eg; I have seen a relatively low powered engine, with a very large wastegate, move up and down 0.3 bar in its boost as the boost control circuit struggles to keep up with this open, closed, open, closed requirement.

----------------------------------------------------------------------------

Enough theory down to the practifcal stuff;

As many will remember I got 40+ guys on this forum to fill out a few simple questions on their car. I then compared what the formula came up with for the wastegate size and what their car actually had. In 35 out of the 40 cars, the formula came up with the same wastegate sizes as they had. In 2 cases it was one size different, but when I checked these 2 further out I found that the guys had actually told the wastegate supplier that they wanted to run more boost than they actually were. So the formula was right, they just had the wrong size wastegate. In one case they guy had moved down a size in turbo after a failure.

Now these wastegates had been specified by a number of well known turbo experts from GCG, Peter Hall, CAPA etc locally or had come in kits from HKS or Trust. Better still the guys seemd pretty happy with the results.

This was all done over 18 months ago and since then I have used the formula to select 5 or 6 wastegates. I have been very happy with the results, as have the drivers. Good horsepower and good response, why wouldn't we be.

Enough for now

[GTR-NUTTER]

sydneykid fancy sorting out what size wastegate i need, as i mhaving trouble making up my mind i have been told to run a 38mm for the following turbo

T4/T51 turbo , 54 trim T51 wheel in S04 compressor housing. Turbonetics Q trim wheel in .70 divided housing with T4 foot and V-band discharge

plz help i need to get one assap

K

[Sydneykid]

sydneykid fancy sorting out what size wastegate i need, as i mhaving trouble making up my mind i have been told to run  a 38mm for the following turbo

T4/T51 turbo , 54 trim T51 wheel in S04 compressor housing. Turbonetics Q trim wheel in .70 divided housing with T4 foot and V-band discharge

plz help i need to get one assap

K

What's your power target? What boost? I have a T51 56 trim compressor map and a T04 54 trim, but no T51 54, if you have the correct compressor map I can easily work out max power and boost. That will give an exact result.

In the interim, looking at the T51 56 and T04S 54, it looks to be around 47 lbs of air per minute at 1.6 bar. Good for ~500 bhp

47 / 23.5 * 19 = 38 mm wastegate.

So if you power target is 500 bhp with your engine specs and you can run 1.6 bar, then 38 mm is what the formula suggest would be the ideal size.

Hope that is of some help

[japsky33]

A smaller wastegate can also create to much back pressure in the manifold can also create boost creep at higher rpm. With the wastegate fluctuating the boost you thought by .3 bar on a lower powered engine I dont see the wastegate as the problem id point towards the manifold design or the boost controller, or did changing the gate fix this issue ?

The wastegate going up and down alot more then a smaller one ? In theory wouldnt the larger wastegate help ramp on to boost quicker with less backpressure ?

as you have said in your theory is that a wrongly matched turbo will cancel out your wastegate issues anyway exactly pointing at (2) A larger wastegate will not effect holding your boost levels if your turbo is matched correctly and your boost controller is doing its job.

Considering your argument work this out for me and tell me what wastegate would be suitable

RB25 standard, T3/T4 400HP @ 20psi .63 back looking at 20psi to create around 260rwkw. tell me what size wastegate ? I can give you more info if needed

BR,

JH

OK lets start off with the theoretical stuff, posted some time ago.......

1. The wastegate size is relevant to how much horsepower you are targeting

2. If you want to run high boost, then a smaller wastegate is better than a larger wastegate. The idea being that in order to generate high boost you need most of the exhaust gas going through the turbine, not through the wastegate.

3. If you want to run low boost then a larger wastegate is better than a smaller wastegate. The idea being that in order to keep the boost low you need a lot of the exhaust gas going through the wastegate not through the turbine.

But what is high boost? Well for the sake of this discussion I have settled on 1.2 to 1.4 bar (18 to 21 psi) as being the divider, thus 1. 2 bar and under is low and 1.4 bar and above is high. How did I arrive at this number? Well based on the results of the surveys, this seems to be the most common point where the wastegate sizes change from theory 2 to theory 3 (above).

The next bit of theory is that it takes 1 lb per minute of airflow to make 11 bhp in a current generation 4 valve engine. This is a pretty well established piece of turbo sizing philosophy. But how do we relate this to wastegate sizing? Well referring to the results of the surveys, it seems a straight 1 to 1 relationship is not too far from the average, so 1 lb of airflow = 1 mm of wastegate diameter.

What I am trying to do with the formula is give a baseline, something to think about. An 85% fit type of thing. At the moment there seems to be a majority of guys wanting external wastegates who don't even know where to start. They have been told for big horsepower you need a big wastegate, which is not necessarily true. They have been told you can't have too big a wastegate, which is definitely not true. They have been told for high boost you need a big wastegate, which again is not necessarily true.

In order to do this there is one main assumption, that the turbo is pretty much the optimium size for the target power and boost. If it is totally wrong then whether the wastegate is sized correctly or not is really irrelevant. The turbo / engine mismatch is gunna kill horsepower / response anyway.

A a 50mm wastegate valve is going to weigh twice as much as a 35 mm one. So there is an inertia issue to be considered. I think that is really the crux of the problem. The diaphram has to move twice as much weight, in and out very rapidly. This has 2 undersirable effects incomparison to a smaller (more correctly) sized wastegate.

Firstly the too large a wastegate has to open and close more often, as it has too little exhaust flow when closed and too much exhaust flow when open. This wears the diaphram, due to the requirement for more movements and more weight.

Secondly all this opening and closing of the wastegate affects the amount of exhaust flow though the turbine, this leads to fluctuations in the boost control. eg; I have seen a relatively low powered engine, with a very large wastegate, move up and down 0.3 bar in its boost as the boost control circuit struggles to keep up with this open, closed, open, closed requirement.

----------------------------------------------------------------------------

Enough theory down to the practifcal stuff;

As many will remember I got 40+ guys on this forum to fill out a few simple questions on their car.  I then compared what the formula came up with for the wastegate size and what their car actually had.  In 35 out of the 40 cars, the formula came up with the same wastegate sizes as they had.  In 2 cases it was one size different, but when I checked these 2 further out I found that the guys had actually told the wastegate supplier that they wanted to run more boost than they actually were.  So the formula was right, they just had the wrong size wastegate.  In one case they guy had moved down a size in turbo after a failure.

Now these wastegates had been specified by a number of well known turbo experts from GCG, Peter Hall, CAPA  etc locally or had come in kits from HKS or Trust.  Better still the guys seemd pretty happy with the results.

This was all done over 18 months ago and since then I have used the formula to select 5 or 6 wastegates.  I have been very happy with the results, as have the drivers.  Good horsepower and good response, why wouldn't we be.

Enough for now

[Sydneykid]

1. A smaller wastegate can also create to much back pressure in the manifold can also create boost creep at higher rpm.

2. With the wastegate fluctuating the boost you thought by .3 bar on a lower powered engine I dont see the wastegate as the problem id point towards the manifold design or the boost controller, or did changing the gate fix this issue ?

3. The wastegate going up and down alot more then a smaller one ? In theory wouldnt the larger wastegate help ramp on to boost quicker with less backpressure ?

4. as you have said in your theory is that a wrongly matched turbo will cancel out your wastegate issues anyway exactly pointing at (2) A larger wastegate will not effect holding your boost levels if your turbo is matched correctly and your boost controller is doing its job.

5. Considering your argument work this out for me and tell me what wastegate would be suitable,  RB25 standard, T3/T4 400HP @ 20psi  .63 back looking at 20psi to create around 260rwkw. tell me what size wastegate ? I can give you more info if needed

BR,

JH

Hi JH, I have numbered your questions as it makes answers easier...

1. But then the wastegate would be too small, but since the formula is based on the airflow from the turbo, that is not possible. Well, unless the turbo is too big, but as I said before it doesn't matter what size wategate you put on, if the turbo is too big you will have lousy response anyway.

2. Changed the wastegate from a 55 mm to a 38 mm and no more surging boost. The guy was told "you can't have too big a wastegate". :zap:

3. Up to the target boost (set by the boost controller) the wastegate is closed, so what size it is is irelevant. So too large or too small, makes no difference to boost build.

4. A wastegate will open according to the pressure applied by the wastegate actuator, but if it is too large it will bypass too much exhaust. If it doesn't bypass too much exhaust, then obviously it isn't too large. If it bypasses too much exhaust then the boost will drop, when the boost drops the wastegate actuator will close and the boost will rise again.

Note that this is accomplished by pneumatic pressure, it is not instantaneous (like electrical switching). So you get surges of air pressure travelling through small pipes that consequently take time to open and close the wastegate. Hence you get surges in boost.

5. 260 X 1.34 + 90 = 410 bhp

410 / 11 = 37

37 / 20 *19 = 35 mm wastegate

Hope that helps :Party:

[GTR-NUTTER]

sydney kid you have pm

thanx

K

[japsky33]

Hi SydneyKid

sorry for the delay been to busy.

1) straight connection to wastegate ie no boost controller involved the wastegate dosent just snap open at exactly 7psi it actually creaps open could be causing the smaller wastegate to be fully opening/closing all the time where as a larger diam wastegate would only for instance need to be opened halfway. Back to your theory on causing damage to the diaphram from opening/closing to much if you look at it that way actually reverses what you was saying.

As for your 35mm wastegate theory there I have to say that we have a 38ml on this car I told you about and it wont hold boost fullstop. There is just to much exhaust velocity to stop the turbo from spooling with that small a wastegate on this application, your theory did not work on that car.

BR,

JH

Note that this is accomplished by pneumatic pressure, it is not instantaneous (like electrical switching). So you get surges of air pressure travelling through small pipes that consequently take time to open and close the wastegate. Hence you get surges in boost.

5. 260 X 1.34 + 90 = 410 bhp

410 / 11 = 37

37 / 20 *19 = 35 mm wastegate

Hope that helps :Party: