GT2 Turbochargers Explained
Added one opinion in bold above.
In the reply quoted below is an example how differently VTGs (or any turbo'd engine) can be tuned.
Ie one can stuff mismatched compressor/turbine turbos into a car and with tuning tricks plus short dyno runs still quote massive (read: IRL excessive) power gains and fast times in third/fouth gear runs. Or at 1/4 mile... Yet if that combination is pushed to the edge at one mile run the real nature of this system is revealed.
Unfortunately this test was stopped too early (at 80 mph / 130 kmh), I also would have liked to see what would have above 250 kmh (155 mph) with this turbo/IC combination. According to my own experience the IAT (with GT2 RS ICs) starts to stabilize after that with increasing airflow through the ICs. See the graph above. Total deltaT was 27C and IAT stayed well below Ign pull threshold (55C / 131F).
That airflow just can't be duplicated in chassis dyno runs, unless you perform it in a windtunnel... Engine dyno is a different animal, there you can simulate that flow increase with controlling air-to-water ICs' water temperature.
In the reply quoted below is an example how differently VTGs (or any turbo'd engine) can be tuned.
Ie one can stuff mismatched compressor/turbine turbos into a car and with tuning tricks plus short dyno runs still quote massive (read: IRL excessive) power gains and fast times in third/fouth gear runs. Or at 1/4 mile... Yet if that combination is pushed to the edge at one mile run the real nature of this system is revealed.
Unfortunately this test was stopped too early (at 80 mph / 130 kmh), I also would have liked to see what would have above 250 kmh (155 mph) with this turbo/IC combination. According to my own experience the IAT (with GT2 RS ICs) starts to stabilize after that with increasing airflow through the ICs. See the graph above. Total deltaT was 27C and IAT stayed well below Ign pull threshold (55C / 131F).
That airflow just can't be duplicated in chassis dyno runs, unless you perform it in a windtunnel... Engine dyno is a different animal, there you can simulate that flow increase with controlling air-to-water ICs' water temperature.
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OK, could you then post a graph with speed?
Got my hands on a set of 997.1 GT2 Vtg's recently & sent them out to Tial for 68 mm Htz wheels looking forward to getting them back to compare to my 68 mm non GT2 Cms vtg's that have the older technology Hta wheels ,expecting them back any day now.
Last edited by twturbo; Sep 29, 2016 at 11:43 PM.
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Why not use the Champion cold side and the larger GT2 hot side and you should have a almost perfect VTG set up?
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Hi Tom, how would I find out if I have the hta or htz wheel on my Champion 68s?
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can champion or others show the members what a GT2 Cartridge Looks like in Comparison to a GT2RS??
Why can the 2RS run 1.6 bar, is this on the same rods as the GT2/Turbo or are the 2RS Rods forged?
I ask i am about to istall stock 997 GT2 Vtgs on my 997 turbo, i do not believe anyone has ever done it.. think of it as an X50 Package for the 997!
Why can the 2RS run 1.6 bar, is this on the same rods as the GT2/Turbo or are the 2RS Rods forged?
I ask i am about to istall stock 997 GT2 Vtgs on my 997 turbo, i do not believe anyone has ever done it.. think of it as an X50 Package for the 997!
I would make them Hyrbids if I was to fit these turbos as fitting a stock set is a waste of time!!! IMO
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+1 on that
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PLS listen to the above recommendations!
At least re-wheel the cold side to a 65-68mm Billet wheels ($1800-2200 with clipping the hot side tubines). Being the GT2 has a larger hot side you might not need to clip the hotside wheels as the 997 VTG turbos do when we upgrade. Personally I would still clip the hot side turbines myself , even on the larger GT2 hot sides.
Let us know how it comes out.
Last edited by Bobbyfali; Oct 22, 2016 at 01:04 PM.
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Some good points ImI had made there.
He does after all run a Gt2 setup so has some good experience with them.
So I guess the choice is yours. Do you want top end power or lower down torque?!
For me I've always been interested in top speed runs.
He does after all run a Gt2 setup so has some good experience with them.
So I guess the choice is yours. Do you want top end power or lower down torque?!
For me I've always been interested in top speed runs.
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This is exactly how a GT2 VTG with larger compressor wheel 997 t feels to me. 9e use Todd for re-mapping so I would not be surprised if its very similar to the GT2 you drove in power delivery.
If you have look at the dyno graph below you can see the torque comes in much later then stock. There's more torque than stock but peak torque has moved from 2000 rpm to 4000 rpm. I don't mind chasing the torque and peak hp as its more exciting than stock but much less efficient than stock turbos in day to day driving in my view.
Also with this GT2 hybrid set up boost is held back to 1.2 bar in the 1st, 2nd and 3rd gear to protect the engine. Its only in 4th gear and above that you get 1.3 to 1.4 bar in the GT2 set up via 9e/Proto.
On track yesterday I was on a circuit where you could drive the whole circuit in 3rd gear. My complete lack of talent didn't help
but I was a whole ten secs slower around this circuit than a gen 2 991 turbo S and 8 secs sower than a 991 GT3 RS sit was hard to keep the turbo on boost.
In fourth gear and above in a straight line with this GT2 hybrid VTG turbo set up your car would leave a 991 GT3 RS or gen 2 991 turbo S for dead but in reality on road how often do you get out of third gear?
I'm thinking about going back down to a stock size wheel and running 1.6 bar of boost. 9e have said its no problem to do this. I'd lose out top end but so what? No need for an expansion tank type GT2 air intake either in fact its less efficient than the 997 turbo intake and many GT2 owners switch to the 997 turbo air intake. As far as I'm aware GT2 and GT2 RS run more boost to compensate for their less efficient intake rather than their intake allowing them to run that much boost. Apart from a few top speed events a year where else do you use the top end power other than on the autobahn?
Stick the GT2 VTG turbos on as they are and you'll make an easy 620 bhp which is exactly what I make with GT2 hybrids in non sport mode. Sport mode gives GT2 VTG hybrid approx another 30bhp and 600 ft lbs of torque
GTR Nick I'd love you to drive my car back to back with yours and see what you think mate.
With hindsight I should have just maybe gone for a GT 3071 set up with forged rods from the start. Wouldn't have cost much more than GT2 VTG hybrid set up and you get the quick spool without any of the down side of VTGS. You live an d learn
Few pics from yesterdays EVO mag track day
If you have look at the dyno graph below you can see the torque comes in much later then stock. There's more torque than stock but peak torque has moved from 2000 rpm to 4000 rpm. I don't mind chasing the torque and peak hp as its more exciting than stock but much less efficient than stock turbos in day to day driving in my view.
Also with this GT2 hybrid set up boost is held back to 1.2 bar in the 1st, 2nd and 3rd gear to protect the engine. Its only in 4th gear and above that you get 1.3 to 1.4 bar in the GT2 set up via 9e/Proto.
On track yesterday I was on a circuit where you could drive the whole circuit in 3rd gear. My complete lack of talent didn't help
but I was a whole ten secs slower around this circuit than a gen 2 991 turbo S and 8 secs sower than a 991 GT3 RS sit was hard to keep the turbo on boost.In fourth gear and above in a straight line with this GT2 hybrid VTG turbo set up your car would leave a 991 GT3 RS or gen 2 991 turbo S for dead but in reality on road how often do you get out of third gear?
I'm thinking about going back down to a stock size wheel and running 1.6 bar of boost. 9e have said its no problem to do this. I'd lose out top end but so what? No need for an expansion tank type GT2 air intake either in fact its less efficient than the 997 turbo intake and many GT2 owners switch to the 997 turbo air intake. As far as I'm aware GT2 and GT2 RS run more boost to compensate for their less efficient intake rather than their intake allowing them to run that much boost. Apart from a few top speed events a year where else do you use the top end power other than on the autobahn?
Stick the GT2 VTG turbos on as they are and you'll make an easy 620 bhp which is exactly what I make with GT2 hybrids in non sport mode. Sport mode gives GT2 VTG hybrid approx another 30bhp and 600 ft lbs of torque
GTR Nick I'd love you to drive my car back to back with yours and see what you think mate.
With hindsight I should have just maybe gone for a GT 3071 set up with forged rods from the start. Wouldn't have cost much more than GT2 VTG hybrid set up and you get the quick spool without any of the down side of VTGS. You live an d learn
Few pics from yesterdays EVO mag track day
Just by comparing 7.1 and GT2's compressors charts one can find the fundamental difference. 7.1 maxes out at 0.21 m3/s and GT2 at 0.23 m3/s, both at about 1.4 bar. In hp this equals about 341 vs 373 hp. Custom wheel should bring you more, shouldn't it?
There's a difference in plenums too. My numbers with 997 GT2 (5th gear pull) vs 997 turbo (4th gear pull) plenums:
814 Nm@ 4348 rpm vs 783 Nm @ 4798 rpm (30 Nm more, 500 rpm earlier)
580 hp @ 7072 rpm vs 585 hp @ 6140 rpm (or @ 4500 rpm 520 hp vs 500 hp)
Both 1.2 bar @ 3500 rpm onwards, same tune.
996's ME7.8 is unable to understand this expansion manifold principle/technology/torque curve & temperatures involved and thus does something very awkward at torque peak, resulting a massive dip in both TQ and HP around 5000-5500 rpm. My tuner was unable to solve this, as a matter of fact globally no-one wanted to touch the issue, so I was forced to change to 997 turbo's standard plastic plenums. IMO GT2's plenums would have been better. And they do not explode at higher boost.
There are too many variables to make any real decisions. For example, gas in Europe alone is a lot better in octane then our 93. That alone is HP. That's why my German friend can tune and maintain 12 deg in midrange at 1.45 bar and we struggle 8 deg. Have any of you logged your cars too see how the timing ? Here is why- I had a client stop by with a $30k kit from one of the most popular companies with 68 mm vtgs. I did a 3rd gear pull and the car peaked 1.5 bar but timing actually went negative 1.5 deg at 4400 rpm.
Just wanted to throw that out there.
Just wanted to throw that out there.
i have sold my standard vtg's and have the gt2's
i will be installing them at the end of the month and can report back.
my tuner tells me that if i do his zero clearance kit which consists of abradable coating it will remove the lag issues. there are other tricks he performs that aid the spool time.
based on imi's responses in this thread and our conversations - yes i called him in england to talk turbos hahah i am going to give the stock gt2 units a try.
i will be doing lots of data logging once they go on, in addition i may start running a blend of 100 octane to help with knock retard. my gt2rs ic's really helped reduce this value, i am running 16 degrees lower iat's in similar outside air conditions since i changed out the ic's
if anyone is running a tune without upgraded ic's i feel bad for your motor.
i will be installing them at the end of the month and can report back.
my tuner tells me that if i do his zero clearance kit which consists of abradable coating it will remove the lag issues. there are other tricks he performs that aid the spool time.
based on imi's responses in this thread and our conversations - yes i called him in england to talk turbos hahah i am going to give the stock gt2 units a try.
i will be doing lots of data logging once they go on, in addition i may start running a blend of 100 octane to help with knock retard. my gt2rs ic's really helped reduce this value, i am running 16 degrees lower iat's in similar outside air conditions since i changed out the ic's
if anyone is running a tune without upgraded ic's i feel bad for your motor.
Have you logged your retardation? Anything over 1.2 bar in a warmer climate it will pull timing hard even with coolers. I did back To back logs on the same car before and after a meth kit and the result was Zero retardation and timing Maintained to the T. The euro guys are running 102 shell premium gas compared to the US clients that run 93 at best. Can't even compare the data since the fuel quality alone will make a big difference.
Last edited by markski@markskituning; Oct 23, 2016 at 08:45 PM.