991.2 GT3 - Manual Gear Ratios and Gear Speeds
03-09-2017, 02:14 PM
#31
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1st gear - 50 mph
2nd gear - 78 mph
3rd gear - 109 mph
4th gear - 140 mph
5th gear - 173 mph
6th gear - 213 mph (theoretical, drag ltd at 198)
991.1 GT3 PDK-S from chart above:
1st gear - 49 mph
2nd gear - 77 mph
3rd gear - 106 mph
4th gear - 137 mph
5th gear - 165 mph
6th gear - 191 mph
7th gear - 219 mph (theoretical, drag ltd at 197)
Last edited by GrantG; 03-09-2017 at 02:56 PM.
03-09-2017, 02:41 PM
#33
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Thanks grantg.
I love the low gearing on the GT3 compared to the carrera but I would still like 7th to be more of an overdrive gear. You'd still hit top speed in 7th, but save some gas for long trips.
Low gearing is so key though for the experience. It's the biggest thing holding back the GT4. Hopefully they fix that with the next one.
I love the low gearing on the GT3 compared to the carrera but I would still like 7th to be more of an overdrive gear. You'd still hit top speed in 7th, but save some gas for long trips.
Low gearing is so key though for the experience. It's the biggest thing holding back the GT4. Hopefully they fix that with the next one.
03-09-2017, 02:50 PM
#34
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Top gear's ratio in the GT cars is carefully calculated so that air resistance and peak horsepower intersect. You want to be right at peak hp at top speed in top gear...
The Germans are not going to give up any top speed to save a little fuel in this car (nor should they, imo, for this kind of car).
03-09-2017, 03:38 PM
#35
Accel Junkie,
I would have loved those top speeds in my 991 R! :-)
You already figured out were you went wrong in your calculation. It goes like this:
- The final gear ratio you mention of 3.091 is correct
- However, you need to consider that the effective ratio of the final drive needs to be corrected for the constant ratio. The constant ratio in the R is 1.22
- This way you will get to an effective final gear ratio of 3.77
I checked my gear diagram for the R, and the top speeds at 9.000 RPM would be as follows:
1st gear: 50 mph
2nd gear: 80 mph
3rd gear: 111 mph
4th gear: 141 mph
5th gear: 168 mph
6th gear: 218 mph
All of the above would be the same for the 991 GT3.2.
Happy driving!
I would have loved those top speeds in my 991 R! :-)
You already figured out were you went wrong in your calculation. It goes like this:
- The final gear ratio you mention of 3.091 is correct
- However, you need to consider that the effective ratio of the final drive needs to be corrected for the constant ratio. The constant ratio in the R is 1.22
- This way you will get to an effective final gear ratio of 3.77
I checked my gear diagram for the R, and the top speeds at 9.000 RPM would be as follows:
1st gear: 50 mph
2nd gear: 80 mph
3rd gear: 111 mph
4th gear: 141 mph
5th gear: 168 mph
6th gear: 218 mph
All of the above would be the same for the 991 GT3.2.
Happy driving!
03-09-2017, 03:47 PM
#36
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Thank you - pretty close to our calculations, but some slight differences (are you sure about 5th gear? Maybe 178, rather than 168?). Either way, it's going to be excellent!
03-09-2017, 05:20 PM
#37
Rennlist Member
Well, even if you made 7th gear just a little taller, it makes the top speed lower (since the motor is unable to reach its peak horsepower at 8,250 rpm).
Top gear's ratio in the GT cars is carefully calculated so that air resistance and peak horsepower intersect. You want to be right at peak hp at top speed in top gear...
The Germans are not going to give up any top speed to save a little fuel in this car (nor should they, imo, for this kind of car).
Top gear's ratio in the GT cars is carefully calculated so that air resistance and peak horsepower intersect. You want to be right at peak hp at top speed in top gear...
The Germans are not going to give up any top speed to save a little fuel in this car (nor should they, imo, for this kind of car).
Still all things considered, I would much rather have the lower gearing of the GT3 that the regular 911. I'd rather burn a bit more gas, but really be able to enjoy the car with the gearing of the GT3.
03-10-2017, 03:16 AM
#38
Rennlist Member
There aren't exactly a lot of Rs floating around for opinions to flow forth that freely.
Look at the GT4 crowed, long gears are a major bitching point and the Achilles heel of that cars driving experience. That car his 84mph in 2nd gear. This is monumentally longer. Of course the much higher redline is a part of that which we all really do want regardless.
Bottom line, if you want to row your own and you like pulling to peak power, best to invest in a really good radar detector on the street. And on the track the occasional gear shift may or may not be worth it.
Look at the GT4 crowed, long gears are a major bitching point and the Achilles heel of that cars driving experience. That car his 84mph in 2nd gear. This is monumentally longer. Of course the much higher redline is a part of that which we all really do want regardless.
Bottom line, if you want to row your own and you like pulling to peak power, best to invest in a really good radar detector on the street. And on the track the occasional gear shift may or may not be worth it.
All that being said, the gears for a GT4 are not too tall. the spacing of 1st to 2nd is a big spread, but only not optimal for a fraction of a second after a 1st gear shift. (a fairly wide spacing) however, after that, its is optimal from 2nd onward. this means , it cannot be improved much by changes.
The GT3 997 has a very similar gear box spacing, and a little more RPM to work with.
the main complaint of a few of the GT4 owners is that they want to shift more in the slower speed ranges on the street. Personally, i drive a performance street car with similar gears and same redline, and HP curve, and havent seen any of those issues. (track or street driving) But, that is a matter of preference. some want to run through 3 or 4 gears before running to 100mph, but with the GT4 it is not necessary for performance, and in fact ,would provide for unnecessary shifts which waste valuable acceleration time.
Look at average HP for any period you are spending in each gear. (for any speed range on the street or on any particular track) if you optimize this, you optimize its acceleration rate overall.
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ztnedman1 (02-28-2024)
03-10-2017, 03:28 AM
#39
Its MPH 
and the car is drag limited e.g. the car could do the speeds outlined in 6th gear if it had the HP to overcome the drag - which it doesn't.
Using 3.77 @ 9000rpm
1-52mph
2-81mph
3-112mph
4-144mph
5-179mph
6-219mph
and the car is drag limited e.g. the car could do the speeds outlined in 6th gear if it had the HP to overcome the drag - which it doesn't.
Using 3.77 @ 9000rpm
1-52mph
2-81mph
3-112mph
4-144mph
5-179mph
6-219mph
03-10-2017, 03:30 AM
#40
Rennlist Member
not even a 928! (55mph)
03-15-2017, 08:07 PM
#42
Burning Brakes
Thread Starter
Updated original post using my same calc but with the constant flipper gear and I came out about the same as this.
03-15-2017, 10:23 PM
#43
12-17-2018, 08:18 AM
#45
what would these speeds be for max bhp at 8250 in the manual 991.2 GT3 ?