Some Turbo Q&A

[Bogie]

I received PM with some Turbo questions and thought I would share with group. Share both for information, as well as getting any feedback on places I might not be accurate. I'm an engineer, but I'm not a Turbo expert. So here goes:

Is the turbo always spinning?

The turbo is going to be spinning a little, even if it's just to pass the ambient pressure of air into the intake. I will defer to the turbo experts as to how much our turbo spins when the engine is in idle. It can't continuously put positive pressure in the manifold because even though our brakes need time for vacuum to build, we do indeed....eventually....get a vacuum.

Does “all” intake air flow pass through the turbo vanes – all the time? Is it gated to open / close?

Yes, for our Turbo. I don't know enough about the entire family of turbos to know if this is true in all cases. There is no gate for the vanes. There is a bypass valve that can pop when the pressure is too high, but that is to prevent back pressure from entering the vanes backwards.

Would not the intake flow be somewhat restricted due to the inline turbine when it’s not in boost mode?

From a net flow standpoint, not if the vanes are spinning sufficiently, or if the path is sufficient to feed the engine what it needs.

Is there an oil line feeding the turbo? Is there any special maintenance we should know of?

Our turbo is oil cooled using the same oil used to cool the engine. It is maintenance free. Well, you do need to change your oil as specified in the OM.

And I somewhat understand that the intercooler is used to keep the pressurized air cooler? But where does it all come in? Is it after turbo but before cylinder intake or Pre Turbo?

It sits between the output of the turbo and the intake manifold of the engine.

And how much cooler does it really make the air?

The intercooler isn't there to cool ambient air. It's there to cool the air coming off the compressor. Turbos can generate a lot of heat in the air during compression. So air that comes in at 70 degrees might be 200 degrees coming out. That's just an example. I'm not sure what our in/out ratio is, or how much is increased in compression versus how much is from sympathetic heat off the hot side. Whatever temperature it is when it goes in, it's hotter on the way out....sometimes a lot hotter. It doesn't matter if it's winter or summer. If it's hotter coming out than coming in, you're losing power in combustion. The intercooler is designed to take that hot air off the compressor and give it a chance to cool before it enters the intake manifold of the engine. It will still be hotter than ambient (maybe even a good bit hotter), but it will be cooler than it would have been if you crammed it straight from the turbo into the engine intake manifold.

I guess a good way to sum up an intercooler is to call it an interlesshotter.

[MataguaySky]

Thanks Bogie!

I'll have to hunt down the thread, but IIRC Eloy posted some temp numbers from Stock IC and RPI IC on the dyno.

I think it was something like:

Charged Air 230 degrees

Stock IC 96 degrees

RPI IC 84 degress

Ambient was a mid 70's number, maybe 74.

[nomead]

Originally Posted by Bogie

...The intercooler isn't there to cool ambient air. It's there to cool the air coming off the compressor. Turbos can generate a lot of heat in the air during compression. So air that comes in at 70 degrees might be 200 degrees coming out. That's just an example. I'm not sure what our in/out ratio is, or how much is increased in compression versus how much is from sympathetic heat off the hot side. Whatever temperature it is when it goes in, it's hotter on the way out....sometimes a lot hotter. It doesn't matter if it's winter or summer. If it's hotter coming out than coming in, you're losing power in combustion. The intercooler is designed to take that hot air off the compressor and give it a chance to cool before it enters the intake manifold of the engine. It will still be hotter than ambient (maybe even a good bit hotter), but it will be cooler than it would have been if you crammed it straight from the turbo into the engine intake manifold.

I guess a good way to sum up an intercooler is to call it an interlesshotter.

I knew Eloy made reference to his results somewhere... found it here.

[Chris-Chicago]

What is the maximum boost that should display on the information display. In another thread another member mentioned on his RL he never sees more that 18 psi boost, and more like 16 psi is typical. I can get mine to easily hit 25 psi. And my CEL has gone off 3 times, and it's been in the shop 2 times, and the CEL is on again so I'm scheduling 3rd visit when GM Engineer is at the dealership.

[Bogie]

Originally Posted by Chris-Chicago

What is the maximum boost that should display on the information display. In another thread another member mentioned on his RL he never sees more that 18 psi boost, and more like 16 psi is typical. I can get mine to easily hit 25 psi. And my CEL has gone off 3 times, and it's been in the shop 2 times, and the CEL is on again so I'm scheduling 3rd visit when GM Engineer is at the dealership.

I think the max it's engineered to deliver is 20 psi, and I believe anything over 23psi is considered dangerous by the ECM, which is why you are getting a CEL. The 20psi is on the high end of design. I get about 18psi tops.

Looking at the compressor map, 25psi is right at the turbo redline; run it there or above and you risk pretty much ripping your turbo apart.

Have they checked the wastegate setting, and ensured it's set properly and works properly?

They should also check and see if the bypass valve is sticking. You should be able to hear it whistle when the turbo spools and you back off the power. Also, do you get the 25 psi when accelerating or after you back off. If you get it during acceleration, that is often a wastegate problem (but it could be a bypass under certain circumstances). If you get it when backing off, that would be a bypass problem.

Do you feel the power at 25psi? If not, it may be a sensor instead.

[Chris-Chicago]

I definitely feel the power of 25psi, the car takes off like a rocket, and I'm under 5,000 rpms. I do hear the whistle when taking my foot off the gas, so it would seem like the gate is working. But it ramps up to 24 & 25 PSI real easy, and continues to do so even after CEL goes off. And oddly one day the turbo was staying down around only 4-5 psi, then the next day and ever since it's putting out maxium speed. I will make sure I bring the PSI issue up to the service department when I bring it in. Thanks for the support !!!!

[Bogie]

I do hear the whistle when taking my foot off the gas, so it would seem like the gate is working.

Bypass is working.

But it ramps up to 24 & 25 PSI real easy, and continues to do so even after CEL goes off.

Sounds like a wastegate problem.

And oddly one day the turbo was staying down around only 4-5 psi, then the next day and ever since it's putting out maxium speed.

Interesting. The 4-5 psi mode is triggered when ECM detects a problem. I wonder, what is the primary mechanism the ECM uses to drop the psi? It might be the wastegate command. And if the wastegate is the failure point, it might not be responding to the command properly. I would think there should be some other mechanism to address a wastegate failure of this kind, but...oh well.

I'm just speculating here from an engineering perspective....grabbing at possibilities.

[Chris-Chicago]

thanks. I'm still waiting for service department to call me back to let me know GM Engineer is available. I will print out your input for them. One of the service managers has been using the Skyforum already for trouble shooting, thanks to great people such as yourself. Thanks again. Chris

[RedSkyWV]

It's great to here the people are reaching out to others more informed than themselves instead of just throwing parts at it, but it's honestly a little scary that they need to come here to get advice on their own equipment....

[Bogie]

Originally Posted by RedSkyWV

It's great to here the people are reaching out to others more informed than themselves instead of just throwing parts at it, but it's honestly a little scary that they need to come here to get advice on their own equipment....

Yes and no. As long as those who come here take everything with the proverbial "grain of salt", it should be OK. A Service Manager of Tech has to understand information on this board is suspect, and must learn to filter the information properly.

At the service level, things run procedurally. Procedures have their root in engineering, but attempt to remove as much engineering as possible from the procedure. When a failure occurs, procedures are designed to locate the problem, and then provide step by step guidance on fixing the problem.

90% of the time, it works great. But what happens when you follow all the checklists and procedures, and the problem doesn't go away? That's when a bit of engineering knowledge comes in handy. If you know how things operate, you can figure out what the procedures are trying to locate and fix. And the engineering knowledge might let you realize the procedures aren't looking at something that could cause the problem. So, you go take a look at the part the procedures missed, and see what's up. Maybe you find a new fault node.

Engineering <-> Tech

It's a two way street. Engineers feed the techs with procedures. Techs feed back to engineers things that the procedures didn't catch. Engineers update procedures to cover what they missed, and send back to Techs.

So, coming to these forums help in two ways:

1. Gives techs engineering insight into the procedures they implement.
2. Gives techs possible feedback nodes to send back to (or ask) engineering.

Oh, and it also give the engineers direct feedback on our problems. We could be totally off base on cause, but the simple fact we're discussing a problem could clue in an engineer on the real cause, resulting in a fix. We don't even need to be correct in our diagnoses to provide useful feedback. And lastly, several folks who own the cars are true auto techs and auto engineers (I'm not an auto engineer), and can provide true insight into what's going on sometimes.

As long as the information is used responsibly (as an additional source of "possibly useful" information), it's a good place to be.