Bolt on turbo kit (7 Viewers)

[subzali]

If you would like to play the google game please go google turbo back pressure or drive pressure effects on wastegates. Cutting and pasting does not make up for experience. The spring pressures are estimates based off of backpressure/drive pressure, the location of the wastegate as well as the flow of exhaust will determine how the wastegate operates because the exhaust pressure pushes on the valve. It is the back pressure/drive pressure + the positive manifold pressure that overcomes the spring, and in almost every single case the back pressure/drive pressure is greater than the positive manifold pressure. If you do not reach the back pressure and only had the positive manifold pressure it would not open the wastegate.


Quoted directly from "FIVE ‘FACTS’ ABOUT WASTEGATES THAT ARE WRONG"
* Note: this spring function is explained for a dynamic condition when installed on a vehicle. The spring is designed to include elements of back pressure / airflow – if bench testing a waste-gate you will expect a higher crack pressure.

Five ‘facts’ about wastegates that are wrong - Turbosmart

Wastegates are one of the most commonly misunderstood pieces of the turbocharging puzzle. These devices are responsible for regulating boost by allowing exhaust gasses to bypass the turbine of the turbocharger, making sure the compressor does not spin too quickly and produce too much...

www.turbosmart.com

I’m not trying to play a game I’m trying to understand. Thanks for the links I will go take a look.

My experience is that the boost pressure I see on the gauge at full boost with wastegate actuated does not change with altitude. It’s always 6. This is with a setup similar to the Tial that’s being provided with this kit, that’s why I searched for it because I wanted to make sure it operates the same and we’re not talking about different things.

What I am hearing you say is that as altitude increases the boost gauge pressure at full boost with wastegate open will increase because the turbo is trying to achieve an absolute pressure. So if I get 6 psi gauge at 5000 feet I will see 8 psi gauge at 10000 feet, or thereabouts. Am I hearing you right or are we arguing about different things?

 

[AussieHJCruza]

I’m not trying to play a game I’m trying to understand. Thanks for the links I will go take a look.

My experience is that the boost pressure I see on the gauge at full boost with wastegate actuated does not change with altitude. It’s always 6. This is with a setup similar to the Tial that’s being provided with this kit, that’s why I searched for it because I wanted to make sure it operates the same and we’re not talking about different things.

What I am hearing you say is that as altitude increases the boost gauge pressure at full boost with wastegate open will increase because the turbo is trying to achieve an absolute pressure. So if I get 6 psi gauge at 5000 feet I will see 8 psi gauge at 10000 feet, or thereabouts. Am I hearing you right or are we arguing about different things?

I believe you will see 6psi on the gauge - the turbo will be working 'harder' to create the 6psi at altitude because the atmospheric pressure is lower so more boost pressure is required to create the same absolute. If it had a blower, I believe you would see lower boost pressure (Never had a blower so not sure on this one) because a blower is fixed displacement, ie moves X air per revolution, whereas a turbo is not.

 

[Qball]

Ok @NLXTACY, can you start a new thread for the 4/6BT adapter/swap kit? I'm not going to attempt to use the C word.

 

[Minuteman]

Ok @NLXTACY, can you start a new thread for the 4/6BT adapter/swap kit? I'm not going to attempt to use the C word.

^^^^ what he said^^^^

 

[Corbet]

Your Subaru has electronic boost control, this will not. This is relying solely on the spring pressure. With electronic boost control you are right it will not change relative to atmospheric because it is targeting manifold boost levels. Without boost control the only thing opening the wastegate is exhaust manifold pressure and the only thing acting against the exhaust manifold pressure is the spring and the intake manifold pressure. So X lbs of spring pressure + X psi of boost pressure, on the diaphragm and you have to overcome this with exhaust manifold pressure before the wastegate opens so the turbo will just continue to spin adding air until that point. Very different situations.

So to clarify, with an electronic boost control the system adds "x" amount of boost to whatever the atmospheric condition is on the intake side. Where this mechanical system "spring" on the exhaust side is set up to give "y" amount of boost at sea level. But because its on the exhaust side it doesn't really care or know what elevation it's at. Its going allow the turbo to spool up enough pressure or volume to reproduce boost so that total cylinder volume always equals "y" + sea level atmospheric? Meaning the actual boost number in psi will vary with intake atmospheric to always end up at some total value "z" that's a constant? All of this of course at WOT.

I hope I was able to express my questions clearly there.

 

[alia176]

I'm enjoying learning about boost pressure......party on...

 

[Jason Andrews]

So to clarify, with an electronic boost control the system adds "x" amount of boost to whatever the atmospheric condition is on the intake side. Where this mechanical system "spring" on the exhaust side is set up to give "y" amount of boost at sea level. But because its on the exhaust side it doesn't really care or know what elevation it's at. Its going allow the turbo to spool up enough pressure or volume to reproduce boost so that total cylinder volume always equals "y" + sea level atmospheric? Meaning the actual boost number in psi will vary with intake atmospheric to always end up at some total value "z" that's a constant? All of this of course at WOT.

I hope I was able to express my questions clearly there.

To answer your question we need to talk in terms of pressure ratio rather than boost. The PR will increase as elevation increases since the turbo is working harder than it would be at sea level. Yes, the mechanical WG spring will be set and not 'see ambient air pressure.' I don't think this is the exact turbo map for the turbo Joey's using, but if you know how much air the engine demands in lbs/min you can plot the points and see where the turbo is operating based on your current elevation. You want it keep it as close to the "efficiency island" as possible so the turbo is not pushing hot (less dense) air. The only things you can do to control this would be turbo size(compressor wheel), exhaust housing size, and the amount of boost.

 

[Jason Andrews]

Sea level- 14.7 atmospheric pressure + 7lbs boost =1.47 PR
10,000ft- 10.1 atmospheric pressure + 7lbs boost =1.69 PR

I have no idea of the air requirements for a boosted 1FZ-FE and honestly don't know chit about turbo'd gas engines, but it gives you an idea of how to do the math and see where the turbo is running. Borg Warner is pretty good about publishing their maps to should be easy to find the right map! What turbo did you say you were using @NLXTACY ? Was it an S300SX-E? what size compressor wheel does it have? 60mm, 62mm, 66mm? And what size A/R exhaust housing?

 

[NLXTACY]

To answer your question we need to talk in terms of pressure ratio rather than boost. The PR will increase as elevation increases since the turbo is working harder than it would be at sea level. Yes, the mechanical WG spring will be set and not 'see ambient air pressure.' I don't think this is the exact turbo map for the turbo Joey's using, but if you know how much air the engine demands in lbs/min you can plot the points and see where the turbo is operating based on your current elevation. You want it keep it as close to the "efficiency island" as possible so the turbo is not pushing hot (less dense) air. The only things you can do to control this would be turbo size(compressor wheel), exhaust housing size, and the amount of boost.
View attachment 1922221

This is the turbo I’m using

 

[NLXTACY]

Sea level- 14.7 atmospheric pressure + 7lbs boost =1.47 PR
10,000ft- 10.1 atmospheric pressure + 7lbs boost =1.69 PR

I have no idea of the air requirements for a boosted 1FZ-FE and honestly don't know chit about turbo'd gas engines, but it gives you an idea of how to do the math and see where the turbo is running. Borg Warner is pretty good about publishing their maps to should be easy to find the right map! What turbo did you say you were using @NLXTACY ? Was it an S300SX-E? what size compressor wheel does it have? 60mm, 62mm, 66mm? And what size A/R exhaust housing?

62mm compressor, T4 single-scroll, 44mm wastegate and 0.4bar spring

 

[Jason Andrews]

62mm compressor, T4 single-scroll, 44mm wastegate and 0.4bar spring

Edit: .4bar spring is basically 5.8psi boost
Sea level is 14.7 + 6psi boost = 20.7 / 14.7 = 1.40PR
10,000ft is 10.1 + 6psi boost = 16.1 / 10.1 = 1.59PR

So this map then since it's the 62mm variant.

 

[Corbet]

you guys and your tech talk. That is good but for us laymen... this system regulated on the mechanical exhaust side will basically supply the same amount of total air into the combustion chamber regardless of elevation? (removing the discussion of air temp variables due to efficiency of said turbo and what ever demand)

I ask this as my understanding as of now is that the spring on the exhaust side is designed to regulate based on what it is seeing on that side of combustion. And that spring does not see outside atmospheric pressure.

 

[LandCruiserPhil]

No way a quality shop can do a complete HG jobs for $1K including machining and a factory gasket kit. Maybe $1K before labor with minimal parts replacement. But even that is a stretch at today’s prices.

Sure they can
In my case no machine work was needed for a pm HG replacement.

 

[scottryana]

That is correct Corbet, this setup will provide a closer absolute pressure supply than any other type of boost regulation. With other types of boost regulation you are plumbing a positive manifold pressure source to the top of the wastegate and using a lighter spring and it is the positive manifold pressure pushing on the diaphragm that holds the wastegate shut. With out an external boost regulator you are relying on the exhaust manifold pressure pushing on the wastegate valve and the intake manifold pressure on the underside of the diaphragm to open the wastegate. Until the combined pressure is reached the wastegate stays closed. So at altitude you still have to create that amount of exhaust pressure (hence more turbo pressure) before the wastegate opens and bypasses exhaust around the turbo. Since there is a non-linear relationship between intake manifold pressure and exhaust manifold pressure (really depending on exhaust setups) I can not guarantee it will be exact, but it will be closer to maintaining absolute than anything else.

you guys and your tech talk. That is good but for us laymen... this system regulated on the mechanical exhaust side will basically supply the same amount of total air into the combustion chamber regardless of elevation? (removing the discussion of air temp variables due to efficiency of said turbo and what ever demand)

I ask this as my understanding as of now is that the spring on the exhaust side is designed to regulate based on what it is seeing on that side of combustion. And that spring does not see outside atmospheric pressure.

 

[Corbet]

That is correct Corbet, this setup will provide a closer absolute pressure supply than any other type of boost regulation. With other types of boost regulation you are plumbing a positive manifold pressure source to the top of the wastegate and using a lighter spring and it is the positive manifold pressure pushing on the diaphragm that holds the wastegate shut. With out an external boost regulator you are relying on the exhaust manifold pressure pushing on the wastegate valve and the intake manifold pressure on the underside of the diaphragm to open the wastegate. Until the combined pressure is reached the wastegate stays closed. So at altitude you still have to create that amount of exhaust pressure (hence more turbo pressure) before the wastegate opens and bypasses exhaust around the turbo. Since there is a non-linear relationship between intake manifold pressure and exhaust manifold pressure (really depending on exhaust setups) I can not guarantee it will be exact, but it will be closer to maintaining absolute than anything else.

So just a quick follow up question. Since the intake/exhaust pressures are not linear. How does a performance exhaust effect the waste gage? My common sense thinking tells me if air can flow out more freely then the waste does not open as quickly and thus allow the turbo to supply a higher absolute pressure.

 

[Briano]

Sure they can
In my case no machine work was needed for a pm HG replacement.

Just my opinion, but if it’s for PM that means you are in the 200k range, if your in the 200k range and have your head off and choose not to do valve seals I think that would be pointless..... if you choose to do valve seals at that point your head is torn down and it would make sense to do a refresh/ rebuild on the head and a quick resurface! I own an auto repair shop and can’t physically do this on my own personal vehicle for under 1000! Again just my opinion

 

[scottryana]

That is correct and if you look back in the thread when everyone was asking if they should do a 3" free flow exhaust I told them no. I said to stay as close to stock configuration as possible.

So just a quick follow up question. Since the intake/exhaust pressures are not linear. How does a performance exhaust effect the waste gage? My common sense thinking tells me if air can flow out more freely then the waste does not open as quickly and thus allow the turbo to supply a higher absolute pressure.

 

[Corbet]

That is correct and if you look back in the thread when everyone was asking if they should do a 3" free flow exhaust I told them no. I said to stay as close to stock configuration as possible.

Looking back in this thread is somewhat daunting at this point. But I do vaguely remember your statement on the 3”. I’m still running a 2.5” EMS system that I know your familiar with.

 

[scottryana]

Yeah at this point I would't expect people to go back through it. But I just remember people were asking if they were going to replace their exhaust in preparation for the turbo if they should get a 3" high flow exhaust and I specifically said no. For this exact reason. If you reduce that back pressure you don't open the wastegate and you risk running outside the fueling parameters that Joey is going to be testing, CARB certifying, and sending out..

Looking back in this thread is somewhat daunting at this point. But I do vaguely remember your statement on the 3”. I’m still running a 2.5” EMS system that I know your familiar with.

 

[LandCruiserPhil]

Just my opinion, but if it’s for PM that means you are in the 200k range, if your in the 200k range and have your head off and choose not to do valve seals I think that would be pointless..... if you choose to do valve seals at that point your head is torn down and it would make sense to do a refresh/ rebuild on the head and a quick resurface! I own an auto repair shop and can’t physically do this on my own personal vehicle for under 1000! Again just my opinion

FWIW- My PM HG was on a very low mileage an excellent condition cruiser and no other major work was required per the dealership. Today it still runs excellent and under 200K. Im 100% happy and satisfied years later with what I choose to have done at the time for the price.