How stuff works: TURBOS AND WASTEGATES EXPLAINED...
How stuff works: TURBOS AND WASTEGATES EXPLAINED...
hey guys, i just got a call from a guy that I dont believe is on this forum or anything but we had a conflicting conversation about what size wastegate he needed to use on his subaru. He told me that he did a ton of research and he said he wanted to run high boost and that a 38mm wastegate would not be enough for 30+ psi on a GT35R.
First of all, just to put it out there, wastegates LOWER boost, meaning that the lower boost you run, the more of the wastegate you use.
Below is a turbo and how it works basically. The red side is the exhaust side, the blue side is the compressor side. The 2 wheels are connected by a shaft. Exhaust gases turn the exhaust wheel which is attached to the shaft that is attached to the compressor wheel. The compressor wheel sucks in air and compresses it, forcing it through the intercooler pipe and into the engine.
Below is a turbo setup in color. There is no wastegate on this setup. Consider the red tube to be a header or exhaust manifold. With no wastegate on that tube, boost would keep going up and up with rpm to whatever the turbo could produce because the engine would just keep producing more and moer exhaust gases. Now if you put a wastegate on that tube its basically going to act like a controlled exhaust leak and its going to leak out exhaust gases before they can reach the exhaust wheel. The more you leak out, the less the exhaust wheel will turn; creating less boost.
Now heres where we get technical. wastegates will open up to whatever spring pressure the spring inside is because The vacuum line thats hooked up to the lower port has the pressurized air going through it to the gate under the valve assembly forcing it open. Basically if you have a 14.5 psi spring in your gate and everything else is working properly, when you floor your car, your turbo will create 14.5 psi of boost and once theres 14.5 psi of boost in your engine/intake manifold, that means theres 14.5 psi of boost going through that vacuum line. once 14.5 psi of boost hits the wastegate it forces it open, thus bleeding off exhaust and maintaining the amount of exhaust it takes to turn the exhaust wheel to create 14.5 psi. Now imagine we install a manual boost controller in the vacuum line between the intake mani and the wastegate. Now we have another controlled leak. If we leak off 4 psi before the wastegate sees it, then the motor is going to have 18.5 psi in it when the wastegate sees 14.5 psi. As we bleed off more air through the boost controller the boost will go up and up because the wastegate isnt seeing that 14.5 psi yet.
here is a link to a pdf file that shows how all of the above works
http://www.tialmedia.com/documents/w..._wginstall.pdf
Now lastly, there are other factors that will effect boost levels.
Boost creep and cars not reaching the desired boost level are other problems people have.
Scenario 1. If you have a 38mm wastegate on a 8.0L viper which obviously has a ton of exhaust and you want to run 3 psi of boost well whats gonna happen? The gate is gonna maxxed out and the exhaust gases are just gonna turn the exhaust wheel faster and faster creating more boost then desired.
Scenario 2. Imagine we put a stock subaru turbo on a dodge viper with a four 44mm gates with a 3 psi springs. Now we want to run 20 psi of boost and we have a boost controller to do that. Ok now we have plenty of wastegate room to work with so scenario 1 wont be a problem. What would happen? Obviously the TINY exhaust side of the stock subie turbo would be a huge bottleneck for 8.0L of exhaust gas. So we'd want to run 20 psi but we wouldnt reach that number most likely. WHY? because there would be so much backpressure in the headers from the exhaust not being able to squeeze through the subie turbo so well over 3 psi of pressure would build up inside the headers/exhaust manifolds. That would thus force the wastegates open and 20 psi wouldnt never be achieved. This is why people with 7 psi springs cant run 35 psi without their gate opening up. I've seen people pull the vacuum hose off the wastegate completely and the car might only run 24 psi because there is 7 psi of exhaust pressure inside the exhaust manifold when there is 24 psi of pressure inside the engine.
if anyone has any questions please feel free to ask as I'll do my best to explain. There are other things that can sometimes effect boost control such as recirculating, backpressure in the wastegate, backpressure in the exhaust system, etc... but if anyone wants to know about that, just post it. Thanks and enjoy the info guys!!!
-Steve
First of all, just to put it out there, wastegates LOWER boost, meaning that the lower boost you run, the more of the wastegate you use.
Below is a turbo and how it works basically. The red side is the exhaust side, the blue side is the compressor side. The 2 wheels are connected by a shaft. Exhaust gases turn the exhaust wheel which is attached to the shaft that is attached to the compressor wheel. The compressor wheel sucks in air and compresses it, forcing it through the intercooler pipe and into the engine.
Below is a turbo setup in color. There is no wastegate on this setup. Consider the red tube to be a header or exhaust manifold. With no wastegate on that tube, boost would keep going up and up with rpm to whatever the turbo could produce because the engine would just keep producing more and moer exhaust gases. Now if you put a wastegate on that tube its basically going to act like a controlled exhaust leak and its going to leak out exhaust gases before they can reach the exhaust wheel. The more you leak out, the less the exhaust wheel will turn; creating less boost.
Now heres where we get technical. wastegates will open up to whatever spring pressure the spring inside is because The vacuum line thats hooked up to the lower port has the pressurized air going through it to the gate under the valve assembly forcing it open. Basically if you have a 14.5 psi spring in your gate and everything else is working properly, when you floor your car, your turbo will create 14.5 psi of boost and once theres 14.5 psi of boost in your engine/intake manifold, that means theres 14.5 psi of boost going through that vacuum line. once 14.5 psi of boost hits the wastegate it forces it open, thus bleeding off exhaust and maintaining the amount of exhaust it takes to turn the exhaust wheel to create 14.5 psi. Now imagine we install a manual boost controller in the vacuum line between the intake mani and the wastegate. Now we have another controlled leak. If we leak off 4 psi before the wastegate sees it, then the motor is going to have 18.5 psi in it when the wastegate sees 14.5 psi. As we bleed off more air through the boost controller the boost will go up and up because the wastegate isnt seeing that 14.5 psi yet.
here is a link to a pdf file that shows how all of the above works
http://www.tialmedia.com/documents/w..._wginstall.pdf
Now lastly, there are other factors that will effect boost levels.
Boost creep and cars not reaching the desired boost level are other problems people have.
Scenario 1. If you have a 38mm wastegate on a 8.0L viper which obviously has a ton of exhaust and you want to run 3 psi of boost well whats gonna happen? The gate is gonna maxxed out and the exhaust gases are just gonna turn the exhaust wheel faster and faster creating more boost then desired.
Scenario 2. Imagine we put a stock subaru turbo on a dodge viper with a four 44mm gates with a 3 psi springs. Now we want to run 20 psi of boost and we have a boost controller to do that. Ok now we have plenty of wastegate room to work with so scenario 1 wont be a problem. What would happen? Obviously the TINY exhaust side of the stock subie turbo would be a huge bottleneck for 8.0L of exhaust gas. So we'd want to run 20 psi but we wouldnt reach that number most likely. WHY? because there would be so much backpressure in the headers from the exhaust not being able to squeeze through the subie turbo so well over 3 psi of pressure would build up inside the headers/exhaust manifolds. That would thus force the wastegates open and 20 psi wouldnt never be achieved. This is why people with 7 psi springs cant run 35 psi without their gate opening up. I've seen people pull the vacuum hose off the wastegate completely and the car might only run 24 psi because there is 7 psi of exhaust pressure inside the exhaust manifold when there is 24 psi of pressure inside the engine.
if anyone has any questions please feel free to ask as I'll do my best to explain. There are other things that can sometimes effect boost control such as recirculating, backpressure in the wastegate, backpressure in the exhaust system, etc... but if anyone wants to know about that, just post it. Thanks and enjoy the info guys!!!
-Steve
Last edited by StevenStarke; Dec 27, 2007 at 05:42 AM.
99+% of persons in this forum will do fine with 38mm WG. I favor the 44mm, only because I prefer the v-band mounting solution to bolts/gasket.
Regarding spring pressure, I've said this many times before, and I'll say it again. . . I see no reason to run any less spring pressure than the minimum amount of full boost one intends to use. The less amount of external boost control required, the better.
He was misinformed - a common problem.
99+% of persons in this forum will do fine with 38mm WG. I favor the 44mm, only because I prefer the v-band mounting solution to bolts/gasket.
Regarding spring pressure, I've said this many times before, and I'll say it again. . . I see no reason to run any less spring pressure than the minimum amount of full boost one intends to use. The less amount of external boost control required, the better.
99+% of persons in this forum will do fine with 38mm WG. I favor the 44mm, only because I prefer the v-band mounting solution to bolts/gasket.
Regarding spring pressure, I've said this many times before, and I'll say it again. . . I see no reason to run any less spring pressure than the minimum amount of full boost one intends to use. The less amount of external boost control required, the better.
amen to v-band
agreed
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He was misinformed - a common problem.
99+% of persons in this forum will do fine with 38mm WG. I favor the 44mm, only because I prefer the v-band mounting solution to bolts/gasket.
Regarding spring pressure, I've said this many times before, and I'll say it again. . . I see no reason to run any less spring pressure than the minimum amount of full boost one intends to use. The less amount of external boost control required, the better.
99+% of persons in this forum will do fine with 38mm WG. I favor the 44mm, only because I prefer the v-band mounting solution to bolts/gasket.
Regarding spring pressure, I've said this many times before, and I'll say it again. . . I see no reason to run any less spring pressure than the minimum amount of full boost one intends to use. The less amount of external boost control required, the better.
-Steve
38mm vband