might expectate on this coming event, very interesting

 

Manuel - I didn't imply anywhere that this car had VTGs on it. We try to not aim for sub-records and go for the larger overall records, just like we have with the 996 and 997 platforms. In this case the 991 stock motor 1/4 Mile record to add to the 991 stock motor 1/2 Mile record same kit got in Florida.

Agreed - in the GTR world they have "classes" with 58mm and 62mm turbos etc to "differentiate" records because there are so many cars competing and the difference between the turbo groups is in 500hp increments and up to a 1000 pounds of weight reduction. This is not the case here, regardless of what some guys want to believe these cars are in fact in the same class as they are street cars within 50-75hp limited by stock motor, stock clutches and stock trans. We can put GT40s on these and they will still be limited by those factors.

the ET and TRAP are both in fact very close. turbo chargers not as far apart in terms of power potential as you think. the original 68mm HTA wheel which was in the Gen1 68s was a 51mm inducer and a 68mm exducer rated at 51 lbs/ min of airflow. For anyone that knows turbo sizing, these are extremely efficient for their size. That translates to roughly 510 HP per turbo. The new Gen 2 68mm HTZ is about 5-10% more efficient in airflow running at about 55 lbs/min out of that compressor and being good for 540 HP per turbo. Times that by 2 and you are at a hypothetical maximum 1000 crank hp potential from the 68s. Here is more info on the 68mm wheel for you, it was very popular back in the day in the DSM world - note the price for the whole turbo vs what you paid for the same wheels.
http://www.forcedperformance.net/fp-68hta-for-dsm.html

now what we use is in fact dimensionally a larger wheeled turbo from Garrett at GTX3071 Gen 2 which is a 54mm inducer and 71mm exducer that is rated at 34 lb/min and 340 hp with the small hotside and about 50 lb/min and 500 hp with the midsize hotside. optional is the GTX3076 Gen 2 which is a 58mm inducer and 76mm exducer that is rated at 40 lb/min and 400 hp with the small hotside and about 57 lb/min and 570 hp with the midsize hotside which is the largest we use.

so why do we prefer these over the VTGs even though the HP rating is similar?
1. because the hotside on VTGs is so tight that it creates a ton of backpressure and EGTs through the roof when squeezed hard and running at that power is simply past its efficiency range. when a turbo is past its efficiency range it will push higher intake air temps - that is why you had to spray your intercoolers down before racing Shay in Florida and he didn't have to do any of that.
2. better torque management, allowing for more top end HP while keeping the engine happy and internals inside
3. more top end power - a longer highway pull these traditional turbos will come out on top even though on paper they seem close. look at the 1/2 Mile pull video between your car and Shays ES850 car, in the beginning its close and then it runs away from you on the big end but on paper super close 186 vs 184 mph.
4. the cost of a full upgraded VTG package is nearly the same as the cost on a full ES850kit and you actually get 2 brand new full frame turbochargers vs rewheeled stock turbos
5. the cost to install in our shop is the same

again the limiting factor is the stock engine, stock trans.

every generation of Turbo 911s goes thru "upgraded wheel" stage before people end up with Alpha, EFR or other full frame turbos. 993s had the 18Gs, 996s had the 16G, 18G, 20G wheels then 997.1s had 63.5, 65, 66, 68 VTG. oddly enough the fastest VTG 997.1s on the 1/4 Mile and 60-130 up to today are 63.5mm turbo cars. Peek into 997 and 996 forums and you will see a ton of reviews where guys say how much nicer and smoother the 28 / 30 turbos drive with no downsides.

 

Great Post Mark.. I'm in the middle of getting everything ready to install my ES850 kit on my .2. I opted for the G25-660s .. I'll have results posted in the next few months and see what these bad boys can do.

 

Excellent post and very informative. Good to see the breakdown between the different wheel set ups.

 

Thanks Jody - good luck in Florida amigo !

3071 will be lazy with the biggest 1.03 AR, very lazy. there will not be enough shaft speed to make jam. we have tested all 3 hotside ARs .63, .82 and 1.03. We use the small and the medium - application dependent. The 3076 will make more power per pound of boost especially in the upper RPM range at slight expense of spool. We also use Xona variants of same size/flow rating turbos and the G25-660s as well.

Another big advantage of full frame turbos is that they will make more power safely on pump gas both with and without meth.... so you don't have to be burning 12$/gal race fuel to have close to 800 whp.

Here is the video from a couple runs including the record run, remember this was achieved with stock clutches and PDK too:

 

Hello Manuel, why ask a rhetorical question? You know exactly what the package consists of since you got front row seats in Immokalee.

Why continue to play these games? You claim fastest 991 stock motor record and parade about how little vtgs did it, you are now second and the little vtgs are now a crutch. Is your team going to create new categories each time?. Because my rhetorical question is lets say Fadi's car with the gt2rs VTGS goes faster than 9.37 will the participation trophy be changed to fastest 68vtgs? Thats a rhetorical question because I already know the answer to it.


In reality both cars are limited by the STOCK motor, the only thing far apart is the illusion that these apparently ginormous gt30s are 1200hp capable on a stock motor.

What I would take note of is that you can either bolt on a turbo kit and get the same results while keeping the torque in check. Or push 68vtgs past their efficiency but you have to spend the money on a clutch upgrade .
So you implying that you are doing more with less is untrue, you are spending more elsewhere to get the same results. The reason you need a clutch upgrade is because at around 750whp the 68vtgs will start to make over 700wtq yet you can cap the torque on the 30s as explained above. They are also more efficient and thus make more power on just pump 93 and also pump 93 and meth. So if you remove the smoke and mirrors and make a decision based on real data its very easy to see why one option is better than the other.

 

I am not surprised to hear that a .84 AR didn't work out on a 6cyl single turbo application and that you actually picked up spool by going to a 1.0 . You have 6 cylinders worth of exhaust going out one turbine, with a .84 that is too tight and is effectively making a traffic jam before the turbo and actually slowing down spool. When you do it on a 6cyl and only send 3cyl thru a 1.0 hotside you not only lose a ton of exhaust flow but also only get pulses from 3 cylinders. The turbo struggles to get the shaftspeed it needs to be efficient until pretty high in the RPM band and also re-spool in between shifts.... not as much of an issue on PDK cars as manual cars.

We have a couple ES850 kits on the road optioned with the G25-660 turbos. The G25-660 has a 54mm inducer and a 67mm exducer which is actually 1mm smaller than the 68mm exducer of the upgraded VTGs. These turbos are rated from from 350 - 660 HP depending on which hotside you use and application. They offer a .49, .72 and .92 hotsides. So obviously the T25 .49 will be good for 350HP and middle of the road .72 for about 450-550hp and the .92 for 660 MAX. Good turbos for sure, issue with them is availability as they are often not in stock and have longer lead times.