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I didn't want to hi-jack another thread in this forum, where the topic is interpreting GT2 DME reports, since GT2s very typically show very high levels of Range 1-3 over-revs, and sometimes hundreds of range 4's as well in cars that have 20K-30K miles.
Originally Posted by GreenLantern
Based on what I've seen, it's easy for a non-tracked GT2 to have a *very low* number of range 4's. This isn't the GT3 engine, this one hits 3's and 4's really easily.
As I look into purchasing one of these cars, I'm trying to wrap my head around this, from the perspective of the track experience. The first car I learned to track was a 997 GT3. It would be common on some turn exits to begin bumping against the rev limiter on track out because you weren't quite ready to shift, and that didn't result in an ignition event (an "over rev"). In fact, when buying a 997 GT3 you ideally want to see a DME with no over revs at all.
And in tracking the 991TTS, you're often able to go foot to the floorboards on track out before you're quite pointed down the straight, because the AWD has such monster grip that even 560hp doesn't break you loose (and of course PDK over-revs are never a concern).
But it sounds like in a GT2, you're not only OFTEN bumping the rev limiter before you shift, but that doing so as you accelerate is both common (even if it's technically a "late" shift, if you're trying to keep the engine rpm's between peak tq and peak hp) AND logs as an ignition event.
But it sounds like these beasts have such low redline, monster acceleration, AND such short gearing that you're usually on the verge of shifting too late, given that the optimum shifting point is about 1K below the redline?
And then, many still feel the need (desire) to tune these up for even more acceleration, without changing the gearing? Is there enough rubber available on a 12" rear rim to harness that power, ever? Or is driving a stock GT2 (let alone a 540hp+ tuned one) an exercise in constantly feathering the throttle on turn exit until well down the straight, long past the time when a GT3 driver would have his foot mashed to the floor as his car tracked out, lined up, and began accelerating down the straight?
If you track your GT2 and you've tuned it up a little, is that because you really found yourself thinking, "Damn, how disappointing; I'm not even going 100mph yet and already I'm past the point where I can break these 325's loose? [Yawn]"
Sounds like fun! :-) But how has the tune impacted your track behavior with the car and your gear management in turns where the redline looms before the turn exit does?
997GT2 actually have quite long gearing with a 6750rpm limiter, in fact the power curve rises all the way to the limiter so for maximum acceleration red line shifts are most efficient.
In standard 540PS/700NM form Porsche have set it up like all factory models so that it has traction most of the time the standard chassis handles its power/torque very well.
Increasing to about 600Ps/800NM is a sweet spot and relatively simple and even at these levels there is good grip.
When changing gear fast in a 997GT2 the rev needle tends to jump forward at the point of gearchange, they all do it and I wonder if this is why so many have these high over rev readings ?
I posted this before but it does illustrate the jumping rev counter quite well:
That's good information. I was quoting others in the forum who'd mentioned that the hp curve began falling off about 1K before redline. After reading your post I found some dyno posts that what you say, which certainly supports shifting right at redline.
On the other hand, in your second video, the driver is clearly shifting well into the red zone, which makes me wonder where the rev limiter actually kicks in. Of course, the top-end in these videos also seems to indicate tuned cars, so perhaps in these examples the tuning process also raised the rev limiter setting?
A few thoughts from my perspective and experience.
a) The GT2 has massive torque and delivers it both early and in a fairly linear fashion from 2700 on but peaks starts to dip around 5000 (HP continues up of course).
b) In any setting but particularly a race setting, I would never intentionally bounce the race limiter. Namely because you are losing 10ths killing the ignition when you could already be in the next gear accelerating. That goes for any car, kart, bike, etc. but particularly true in the GT2 where there is just as much usable power waiting to be used at 5000 as 6500.
c) I suspect many (certainly not all) of the rev limiter bounces you read about on this forum related to a GT2, happen on the street and in first and second gear. I also suspect that most happen when a new owner is getting used to the car. It took me a couple of times of bouncing the rev limiter to figure out 1st and 2nd. The GT2 has big torque made available starting at 2500 rpm. It can break the tires loose in 3rd accelerating out from 80 mph. In 2nd, the redline can come real quick but totally manageable with good grip. With cold or bad tires on a dirty street, you'll get tire spin without a doubt - and that causes many to unexpectedly hit the limiter earlier than anticipated. In 1st, you just start thinking about shifting at 3000 and by the time you shift you are at 6500 (and thats if you have good grip :-). You would likely rarely (if ever) see 1st gear on a race track and throttle modulation on the track is much different than the guy that is putting his foot to the floor stop light to stop light on the street (just to see what she's got).
d) In summary, the sweet spot on the GT2 is not 6700 so there really is no need to waste time on the track pushing right to the edge of the rev limiter. Shift at 6400-6500 and keep pulling. :-)
Agree with this entire post. Although I never really get too high in the rpm range unless I'm rev matching at the limit. I have never felt the limiter while accelerating (hard bounce)- not in any vehicles I drive, bikes, cars, boats, karts, etc.
Originally Posted by Reid55
A few thoughts from my perspective and experience.
a) The GT2 has massive torque and delivers it both early and in a fairly linear fashion from 2700 on but peaks starts to dip around 5000 (HP continues up of course).
b) In any setting but particularly a race setting, I would never intentionally bounce the race limiter. Namely because you are losing 10ths killing the ignition when you could already be in the next gear accelerating. That goes for any car, kart, bike, etc. but particularly true in the GT2 where there is just as much usable power waiting to be used at 5000 as 6500.
c) I suspect many (certainly not all) of the rev limiter bounces you read about on this forum related to a GT2, happen on the street and in first and second gear. I also suspect that most happen when a new owner is getting used to the car. It took me a couple of times of bouncing the rev limiter to figure out 1st and 2nd. The GT2 has big torque made available starting at 2500 rpm. It can break the tires loose in 3rd accelerating out from 80 mph. In 2nd, the redline can come real quick but totally manageable with good grip. With cold or bad tires on a dirty street, you'll get tire spin without a doubt - and that causes many to unexpectedly hit the limiter earlier than anticipated. In 1st, you just start thinking about shifting at 3000 and by the time you shift you are at 6500 (and thats if you have good grip :-). You would likely rarely (if ever) see 1st gear on a race track and throttle modulation on the track is much different than the guy that is putting his foot to the floor stop light to stop light on the street (just to see what she's got).
d) In summary, the sweet spot on the GT2 is not 6700 so there really is no need to waste time on the track pushing right to the edge of the rev limiter. Shift at 6400-6500 and keep pulling. :-)
One of the problems with tracking the GT2 is that it is so easy to break traction on corner exit and get an overrev because of that. One cannot treat the gas pedal like an on off switch. Modulation is key. The car has more power than traction. Just yesterday I was talking with a guy a out this problem at Road Atlanta.
The anemic and useless LSD doesn't help things either. One way to help mitigate the issue is to rebuild or replace the LSD with proper Motorsports caliber componentry.
Quick understanding of gear ratios in the cars. First pic is of the difference between the GT2 and GT3/RS ratios. I believe the GT3RS 6th gear is .88 which makes it longer than the narrow body car.
Calculate that out to two different shift points.
When you mate this to the power delivery-
You will see you really don't shift that high. Even if you shift at 6krpm you will be dropped back into the meat of the power, and if you understand the graph you will understand that 4krpm is a nice place to be, at the torque peak. Any time you are past that, you will be accelerating at a slower rate. Simplistic explanation, leaves out a lot of stuff, but hits on some of the points. I'm sure others will interject.
One of the problems with tracking the GT2 is that it is so easy to break traction on corner exit and get an overrev because of that. One cannot treat the gas pedal like an on off switch. Modulation is key. The car has more power than traction. Just yesterday I was talking with a guy a out this problem at Road Atlanta.
The anemic and useless LSD doesn't help things either. One way to help mitigate the issue is to rebuild or replace the LSD with proper Motorsports caliber componentry.
Your diff is the reason why I can manhandle my car even with Super Sports.
Figuring it out is part of the fun and does not take long to find your rhythm. Once you do, you are in for a an exhilarating experience with the 2. Many grins and goose bumps ahead.
Seriously looking forward to it. I started tracking with a 997 GT3, which was lots of fun. Then I moved to tracking my 991TTS, which was faster (on equivalent tires) but less involving (and more expensive -- just my humble opinion, YMMV), though still a blast because it's got such strong pull. I'm sure the GT2 will be a hoot and I look forward to getting my kicks with it for a long time to come!
Yes I realize this is a 6 year old thread but I wanted to bump it to thank those who have contributed to it. I've owned my GT2 for about 1.5 years and it is indeed tricky to drive near the rev limiter, particularly on less than smooth surfaces. I do notice the 'nanny lights' coming on fairly regularly when the suspension un-weights, and more so than my GT3 RS. People here are right to point out you don't need to hold revs all the way to 6750 as rev limiter hits are costly in terms of time lost. The behavior shown in the top video about the sweep well beyond redline is something I've noticed and I would agree it's likely responsible for the Range 4s that are fairly common on these cars. I added the RS LWFW to mine in the last few months and, although it has changed the overall behavior a bit, I'm not sure it has lessened that tendency. Since it's the non-driving season, it's harder for me to add mileage now.
I will say that I've noticed people often misinterpret GT2 over-revs compared to GT3s. Having Range 1-4 on a GT2 is fairly normal and expected, whereas you really have to watch out on GT3s as that indicates mechanical over-revs for every single range.
Fairly easy to over-rev a 997 turbo car. My tuned-turbo was close to base GT2 power. I wonder if the tq/hp profile is any different. Also, any difference in gearing between turbo and GT2?
12-04-2014, 10:51 PM
Tracking a GT2 (and managing over revs)
