lic265

A curiosity question about the turbos-
Do the turbos spin at all times through the RPM range? For example, I can accelerate under moderate pedal pressure and see no boost. Are the turbos only working when boost is present ?

jhbrennan

If the engine is generating exhaust then the turbos are spinning.

lic265

That makes sense, but why no boost ?

pete95zhn

That's totally dependent on turbo's programming. Turbos are spinning all the time, but "freewheeling" is not enough to build boost. For that compressor wheel's speed must be increased by collecting the energy from exhaust gases. On conventional turbochargers that's done with increasing the amount of exhaust gases, ie pushing the accelerator. On VTGs by closing turbine's vanes, even without pedaling it. VTGs can be set either to build boost on idle or no boost at all because of their electronic vane control.
OEM program is of course very conservative and has safeguards built in. Because there's a downside -of course- with early/high boost pressure...for that the vanes need to be in a quite closed position and that rises backpressure and EGTs. Both are unwanted and in VTG case high EGT is outright destructive. IIRC 950C is the max that vane mechanism inside turbine housing can withstand continuously.

lic265

Pete
thank you for you detailed response. I get most of what you said, from a noobie standpoint, but i have a few questions. What does EGT and IIRC 950C stand for? Does "chipping" the car affect VTG programming to give more immediate HP?
From what you said, under moderate acceleration all power is from the motor and not the turbos, am i correct? What would be the HP if there were no turbos; can one infer this from the GT models?

pete95zhn

No problem, here are translations:
EGT = Exhaust Gas Temperature
950C = deg in Celsius, about 1742F
IIRC= If I Remember Correctly

With chip/tune/flash turbos' response can be changed. As you wrote it's a normally aspirated car with moderate accelleration, but only a short while. The beauty of VTG turbos is their adaptability and throttle response...they're building boost almost immediately. As an answer to your question about comparison to GT3's I only can give an educated guess. While the basic engine is the same GT3 has higher CR, more agressive cams and better flowing exhaust so there's a difference in favour of GT3. But how much...?

lic265

Ahh, ok, that sounds good. While we are on this topic: what should the boost read in normal mode - i usually get "O" between 2-5K, but if the pedal if fully depressed then it goes up variably to max of 8-10. In sport mode it will read up to 12 or so.
Is this normal operation?

Doc GTO

The boost should read 12-14 psi in regular mode and 15-17 in over boost sport mode. To get over boost you need to have it in sport mode then you need to mash the gas pedal to the floor quickly and not just roll in it slowly. You will see an up arrow next to the gauge.

phillipj

I love that arrow...

Spatia

Ive never seen that arrow. I will have to try it out later today. I have only had the TT for 2 months and am continually learning more about it. Sounds strange however I just learned a few days ago where the headlight washer button was. Pissed me off though as I had just waxed the car.

floridaBMW

This site and a couple others have a wealth of helpful information, they are invaluable. Regarding the "arrow", keep in mind its only during overboost scenario's and obviously during WOT. While looking for the arrow on the dash be careful. Best to go WOT in a higher gear like 4th. U should see it then.

Ken

speed21

If you don't have Sports Chrono function then you are out of luck. If you do, then select sports chrono, select 4th gear, drop back to 3000 rpms or a bit less and mash the throttle to the floor. The arrow will appear and the 1.2 will show on the gauge. If you delay the throttle in any way i.e. squeeze the throttle on, then it won't activate.

Overboost only activates when the engine is placed in a high load/lag type environment which is only when the engine is at too low an rpms in a high gear such as 4th 5th or 6th when the throttle is floored. Floor the throttle WOT in 1st 2nd and 3rd you can pretty well forget it because the engine speed recovers too quickly.

Check it out. Let us know.