# wastegate question



## Murph (Aug 8, 2002)

This is a small question that has been bugging me for the longest time.

I have read alot about wastegates that open up after enough pressure is created by the partially closed off throttle body, but wouldnt it make more sense for it to be electronically controlled by the throttle rather than waiting until whatever pressure number passes by and it opens up? Or is this the case? For which ones?


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## Murph (Aug 8, 2002)

also, after installing a complete turbo kit, would removing the turbo itself harm the engine at all if the ECU was replaced with something more "stock".


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## psshhgoesmysr20 (May 1, 2002)

What you are refering too is a Blow off valve, or a pressure relief valve. That has a different function from a wastegate. A wastegate regulates boost pressure, as where a blow off valve disipates charged air within the plumbing once it gets cut off by the throttle body so it does not cause compressor surge; detrimental damage to your throttle body, extending your turbo's life. As far as your question goes, Blow Off Valves are controlled by vacuum, when boost is present it keeps the valve closed, as soon as the throttle body closes vacuum causes it to open releasing any charged air.


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## Murph (Aug 8, 2002)

ok, blow-off valve is what i meant, but could you explain to me exactly the function of the wastegate? You say it regulates the pressure. So for example if your turbo is capable of lets say 15 psi and you only want to run 10 it would continuously dump a portion of the pressure?

also, still wondering about the blow-off valve opening and closing.


STILL LEARNING!!! thanks! btw nice website


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## psshhgoesmysr20 (May 1, 2002)

The wastegate regulates the amount of air the compressor see's, by releasing the air at a specific reading. A wastegate reads off of boost pressure. A certain pound spring is placed within the wastegate, when the wastegate see's a designated amount of air say .65 bar, the diaphram will open releasing excess air so it does not go above .65. You can always fool the spring to see less air with a manual or electric boost controller. So even though your spring is at .65 you can still boost 1 bar of pressure or 1.2. Basically the boost controller works off of vacuum, fooling the spring to see less air then is actually present. But, if you have a .65 bar spring you can't boost less then .65 bar.

As far as the BOV is concerned, I'm failing to see what you realise. Allow me to reiterate, the BOV reads off intake manifold pressure. That means when the throttle body is open it's reading boost, that boost keeps the valve closed. When the throttle body closes the intake manifold sends a vacuum reading to the BOV causing the valve to open.






Murph said:


> *ok, blow-off valve is what i meant, but could you explain to me exactly the function of the wastegate? You say it regulates the pressure. So for example if your turbo is capable of lets say 15 psi and you only want to run 10 it would continuously dump a portion of the pressure?
> 
> also, still wondering about the blow-off valve opening and closing.
> 
> ...


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## Murph (Aug 8, 2002)

Ok, so one the throttle is released and the intake manifold cuts off the air there is a vacuum inside the intake manifold that sends a signal to the BOV to open up. Now I always thought the BOV was on the turbo itself, and if that is the case is the signal the intake manifold sends electronic or mechanical? Or is the BOV usually mounted somewhere on the intake manifold itself?

I am understanding you and im absorbing what your telling me, im just trying to visualize the mechanics of the wastegate. I thought I had it understood until you mentioned that in the setup you were using as an example you cannot boost LESS than .65bar. I am unable to find any usefull pages on this stuff that I havent read over yet, do you know of any?

and again, thanks


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## James (Apr 29, 2002)

I think you're confusing the two, there's two seperate controls for the boost. The BOV controls the surge of boost after you release your foot off the throttle, it lets the compressed air out and back into the intake or the atmosphere... 

the wastegate controls boost by allowing gas to go around the turbine into the tail pipe... 

when he was talking about the .65 bar he was talking about the wastegate.


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## Murph (Aug 8, 2002)

james, nicely put.


So the wastegate determines as what RPM the turbo engages as to not render the engine powerless at low RPM's.


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## Guest (Aug 15, 2002)

Murph said:


> *So the wastegate determines as what RPM the turbo engages as to not render the engine powerless at low RPM's. *


No, not really. The wastegate determines how much boost pressure you're running. i.e. 10 psi, 15 psi, 20 psi. That's all set by the wastegate. 

All the blowoff valve does is release pressure in your piping when you get off the gas. If you didn't have a blowoff valve, your plumbing would stay pressurized while you're sitting at a stop light for example. It's just a little device to make life easier for your compressor and plumbing - it has nothing to do with how much boost you're running.

The turbo doesn't have a set "engage" point, it doesn't work like that. The turbo is quite literally powered by your exhaust gas. The reason you have "lag" is because at low RPMs, your engine isn't flowing enough air (and hence enough exhaust gas) to spin the exhaust turbine which is what sets the whole thing in motion. That changes as your RPMs rise, because you're flowing more and more air.

At some point, you'll be flowing enough air to start pushing the turbine wheel around. When that happens it's like a chain reaction... when the turbine starts spinning, which causes the compressor wheel on the other side to start spinning. They're connected by a metal shaft. The compressor side starts compressing the incoming fresh air which makes it denser, hotter and faster. then this fast moving hot air goes through your intercooler (hopefully), and goes into the engine even denser than it was before, and this is what gives your engine the ability to make more power.

Then your exhaust gas comes out faster than it was before, which spins the exhaust turbine wheel even faster... and the cycle continues.

The wastegate dictates how much boost pressure you're running. Not when the boost "kicks in", just how much pressure. When the boost comes on is entirely a function of the way the turbo is sized, and your engine. If you have a bigger engine, that means more airflow at low RPMs, which means it'll spool a turbo faster. A smaller turbine wheel is easier to spool up than a bigger one, so a smaller turbine wheel will let your turbo spool up faster.

Chris Allen's Stage 5 turbo is huge... it doesn't make full boost until nearly 5000 RPM. It takes that much air pressure just to spin the thing up to speed. but a stock Bluebird T25 turbo is much, much smaller... that one spools up by 2500 RPM.

This is just a real general description of how it works. if you want more detailed info, there's quite a few sites on the web, and there's some good books available.


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## TUNED200 (Jul 27, 2002)

i have a dsm buddy(91 talon awd turbo) and he helped me with my swap. he was asking me how our wastegate regulates boost, and how we install a aftermarker boost controller. i told him i didnt know, and forgot to ask until now. he is a smart guy, and knows his dsm's, so i thought i would ask.


Brian


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## Slow 96R (Jul 18, 2002)

Zak91SE-R said:


> *
> 
> No, not really. The wastegate determines how much boost pressure you're running. i.e. 10 psi, 15 psi, 20 psi. That's all set by the wastegate.
> 
> ...


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## Murph (Aug 8, 2002)

Zak91SE-R said:


> *
> 
> 
> The turbo doesn't have a set "engage" point, it doesn't work like that. *


 (i thought i read that turbos have engaging points as to not press the used air back through the exhaust valves at low RPMs)

ANYONE HAVE DIAGRAMS OF A WASTEGATE?? 

I think it will be easier to understand the function if i can see it, as your explanations are O K (much appreciated!!!). I thought I had it when James explained it  it made sense when James explained it!!! maybe ill just not know about wastegates


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## Guest (Aug 15, 2002)

Slow 96R said:


> *OK so my ? is why get a larger exhaust if I only have a t28
> Wouldn't my 2.5 exhaust help my turbo be more efficent? *


Not in this case, because there would be too much backpressure. I put a 3" exhaust system on my NX with a Bluebird DET... with a T25, and I picked up about 25 wheel HP, still at 6.5 psi. With a T28, a 2.5" exhaust system is too small and you'll lose some power.


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## Slow 96R (Jul 18, 2002)

Zak91SE-R said:


> *
> 
> Not in this case, because there would be too much backpressure. I put a 3" exhaust system on my NX with a Bluebird DET... with a T25, and I picked up about 25 wheel HP, still at 6.5 psi. With a T28, a 2.5" exhaust system is too small and you'll lose some power. *


OK I know I'm going 3 inch mandrel now!


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## crud in your face (Apr 14, 2003)

a kinda off the subject but, with an external wastegate, the outlet for the excess pressure, is it to remain open or is it to be plumbed somewhere, ie the exhaust system.


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## javierb14 (Jul 9, 2002)

"open loop"
wg venting to atmosphere.....very loud 

"closed loop"
wg rerouted back into exhaust stream

u can do either.


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## ga16det (Sep 20, 2002)

yeah ,but leting the wg dump out is cool  .


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## Guest (May 14, 2003)

and illegal  its like running a straight pipe without the pipe.

just run a closed loop and save our ears eh?


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## [V]igilant[D]river (Mar 6, 2003)

Murph said:


> *(i thought i read that turbos have engaging points as to not press the used air back through the exhaust valves at low RPMs)
> 
> ANYONE HAVE DIAGRAMS OF A WASTEGATE??
> 
> I think it will be easier to understand the function if i can see it, as your explanations are O K (much appreciated!!!). I thought I had it when James explained it  it made sense when James explained it!!! maybe ill just not know about wastegates  *


http://auto.howstuffworks.com/turbo.htm
It's basically so the turbo doesn't spin so fast at high RPM's


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## se-r pastor (Nov 14, 2002)

So is it possible to run an external WG and route it back into the system. My T3 setup is flanged for a Tial and I really don't want to vent to the atmosphere since that would be a cop magnet.


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## ForsakenRX7 (Mar 14, 2003)

Yea you could plumb it back into the exhaust. just route a pipe from the wastegate to the down pipe and plumb it in there.


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## ForsakenRX7 (Mar 14, 2003)

Zak91SE-R said:


> *
> 
> If you didn't have a blowoff valve, your plumbing would stay pressurized while you're sitting at a stop light for example. *


That statement isnt quite true. That built up pressure will find the easiest way to escape. And since it cant get passed the throttle plate its going to go...backwards. Backspinning the the turbo(Not good) which will eventually lead to turbo death. If you ever hear a car with a extremely small BOV, or without one at all they will make this whipple soud between shifts. That sound is the turbo getting closed lined at a full speed run essentially. 

TIP: If any of you guys are looking for a good BOV for cheap, find one off of a 1G DSM. They are the best bang for the buck BOVs you will find ANYWHERE.


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## glide (Apr 29, 2003)

se-r pastor said:


> *So is it possible to run an external WG and route it back into the system. My T3 setup is flanged for a Tial and I really don't want to vent to the atmosphere since that would be a cop magnet. *


 Basic rule of thumb is to route it back in around 18" from the turbo.


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