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I just received my first-ever turbo 911, and I'm wondering if it's working right. There's a number of issues with it. Most of them are typical of older cars, and I'm not too concerned. But the big one for me is the boost. I used to have a 2011 Subaru WRX. You'd put your foot down, and slowly accelerate until about 3500RPM, when all of a sudden you're launched back in your seat and have to shift. It was fun, but the lag was infuriating. I was under the impression that my '08 997TT would have a different experience. And to a point, it does. Off-boost, there's enough power to feel like an average car. By contrast, the WRX felt slow. The 997.1 doesn't. But it's still got that 3500RPM foot-down on/off switch. I guess I was expecting the VGT to smooth the power out a bit and feel more like a supercharger. Instead, it feels like a bigger, better Subaru. A much, much better Subaru. So. Is this normal? Do the VGT operate like any other turbo? Or should I add this to the list of things the dealer needs to check out for me?
It sounds normal to me. That's part of the Porsche 911 turbo experience. If you have a chance to drive a 996 turbo without VTG, you'll be able to tell the difference.
Sounds about right and can be improved a little with custom tuning and/or sport mode. It's certainly not going to feel like a supercharger experience. Turbos don't spool up to 3k+ rpm. Until you're in that range the fun doesn't begin.
I just received my first-ever turbo 911, and I'm wondering if it's working right. There's a number of issues with it. Most of them are typical of older cars, and I'm not too concerned. But the big one for me is the boost. I used to have a 2011 Subaru WRX. You'd put your foot down, and slowly accelerate until about 3500RPM, when all of a sudden you're launched back in your seat and have to shift. It was fun, but the lag was infuriating. I was under the impression that my '08 997TT would have a different experience. And to a point, it does. Off-boost, there's enough power to feel like an average car. By contrast, the WRX felt slow. The 997.1 doesn't. But it's still got that 3500RPM foot-down on/off switch. I guess I was expecting the VGT to smooth the power out a bit and feel more like a supercharger. Instead, it feels like a bigger, better Subaru. A much, much better Subaru. So. Is this normal? Do the VGT operate like any other turbo? Or should I add this to the list of things the dealer needs to check out for me?
Working as intended. The VGT's are meant to maintain efficiency from the beginning to end of the power band / boost range. There does however need to be a minimum amount of air flowed through the compressors for them to be efficient. Compressor size and plumbing/ motor CFM are the main factors that go into this, the twin scroll setup on bmw's for instance are designed for full spool / peak torque at 1200-1500 rpms. That gives you great low end torque and moderate to nice medium range but peeters out up top. The setup on the 911 even with VGT's is rated for a particular CFM to get going which is at 3000-3500 rpms. Short of a drastic change to the setup you will not see much difference in spool times as turbos are flow limited/ dependent. One method for instance would be developing or installing anti lag but that comes at a few costs (mainly wear and tear). As far as usable torque within city driving / rpms there wont be much to gain, as you're experienced with the subi.
I just received my first-ever turbo 911, and I'm wondering if it's working right. There's a number of issues with it. Most of them are typical of older cars, and I'm not too concerned. But the big one for me is the boost. I used to have a 2011 Subaru WRX. You'd put your foot down, and slowly accelerate until about 3500RPM, when all of a sudden you're launched back in your seat and have to shift. It was fun, but the lag was infuriating. I was under the impression that my '08 997TT would have a different experience. And to a point, it does. Off-boost, there's enough power to feel like an average car. By contrast, the WRX felt slow. The 997.1 doesn't. But it's still got that 3500RPM foot-down on/off switch. I guess I was expecting the VGT to smooth the power out a bit and feel more like a supercharger. Instead, it feels like a bigger, better Subaru. A much, much better Subaru. So. Is this normal? Do the VGT operate like any other turbo? Or should I add this to the list of things the dealer needs to check out for me?
A tune changes the ball game with the 997tt as does it with the 996tt. A 996tt stock feels underwhelming where a 997tt feels good but not earth shaking. Smoothing out the welds on the headers on either car does a world of difference as well as opening up the exhaust to a full 3" system.
TeeJay,.. I came out of Subarus also. An '04 STI that made 400 ish at the wheel.
When I got to the 997.1 TT,.. I was thinking the mediocre spool-threshold was a result of the turbos. BUT IT'S NOT. It's in the ECU.
I tune "can" improve that,.. but often it will not. There's perhaps 3-4 reasons why they do it this way. Emissions,.. or staying true to the feel of the older turbos,... But mainly I think it has to do with the rods. Too much torque at the engine's peak VE will cause a huge load on not only the pistons ring-lands (big issue with Subbys),.. but also the con-rods.
I had tunes, bigger inter-coolers, injectors etc, etc,.. and still the onset of boost wasn't much sooner than stock.
Then I had my turbos modded to the 63.5 VTG. The boost was actually coming in at just over 3k. And the tuner was dialing them BACK so they didn't come on until 3,500.
I then realized they need to spool that late to keep from bending the stock rods.
So if you really want earlier spool,.. you'll want to have the cases split, and forged rods installed. Then a great tuner like SAM at ByDesignAuto will LET YOU have spool threshold a little earlier.
I have a built 3.8 Metzger, Sam did my engine and setup and also have improved GT2 turbos pushing 800 whp on pump gas and 900 whp on E85. Even with a built engine, Sam brings on the boost slowly from 3 to 3,500 rpm then explodes after that point. Have to be cautious of torque management most importantly and your able to put that kind of power to the ground without turning it into a widow maker.
I have used the upgraded VTG turbochargers and tune from ES Motors. As compared to the stock power delivery, the modified VTG with the tune felt even more linear delivery of power. When I say linear, it means that from the time i smack down the throttle (from a standstill), there was a wee bit of lull, but then all hell breaks loose. The surge of power is relentless. Of course I have the the AMS big I/c's, the Y pipe, the silicone hoses etc. I was running the stock injector's and engine. I never felt the huge surge around 3k-3.5k rpm. It was explosively linear. What really helped to improve the performance was the fact that I had to send few logs to Emre @ ES motors, based on which he would fine tune the tune, which i would upload to the car. Probably you might need to check the VGT vane activation rods. At times, due to age, they do not move so freely. A little WD40 might help. Or you can ask your workshop to check.
Here is the stock compressor map. This is something to understand as to how/ when a turbo begins to build boost and "spool". The other half is understanding the CFM the engine is capable to delivering at a particular RPM. To repeat the obvious, the 3000-3500 range for you to feel the boost is what the design of the turbos allow for. Unless you change to sequential, twin scroll, or some other hardware modification you will not be changing when/ how the turbo spools in a drastic way.
Put the car in Sport mode and manually shift if a Tip. Go thru the gears around 3,500 to 4,000 rpms at part throttle. Drive it, no need to floor it to redline, just dont drive it like a mini van.
The computer will learn your driving style and adjust for max fun. I have a Tip and rarely have it in Auto, except maybe in stop and go. I think the VGT design is pretty effective in reducing turbo lag. Throw on a exhaust and a tune, guaranteed smiles and you will love the howls of VGT.
Since I don't think anybody has mentioned it, if you're concerned that the variable part of the turbo might not be working, there is a rod for each turbo that controls the inner vane geometry. Those rods are exposed and should move with just light hand pressure. I don't have a pic handy, but I'm guessing a google search will turn it up.
Mine works as intended, but I have the same opinion on it as you. Trying to do an autocross gets frustrating as the straights aren't long enough to use the boosted power effectively. Short straightaways mean that boost is just coming on right when I need to brake for the next turn...
02-25-2019, 03:04 PM
Variable geometry turbo "spool"
