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Back on the original topic. An earlier post suggested to swap in the transmission from the 2.7. Apparently that was going to fix the gear spacing and strength was assumed to be the same.
What about that?
Is it this simple?
Agreed not sure why no one is trying this. Way simpler and costs less then a gear change. To top it off your stock gearbox remains untouched and can be reinstalled at any point. Worst case it doesn't bolt up you could sell it. If I had the spare cash I would give it a try.
Official ratios from Porsche: http://press.porsche.com/vehicles/20...pecs_Final.pdf
Left 981, Right 981S (=GT4)
That's 5.1% more torque to the wheels in 2nd gear. Will effectively raise 308ftlb to 324ftlb.
Also reduces top speed in 2nd gear by 4mph.
Even more improvement in 1st: 11% increase of torque to the wheel.
It almost seems that this is the transmission AP wanted to put in, but wasn't allowed to !
Back on the original topic. An earlier post suggested to swap in the transmission from the 2.7. Apparently that was going to fix the gear spacing and strength was assumed to be the same.
What about that?
Is it this simple?
tis' simple but its' 10k more or less.
everying porsche is 10k here 10k there
Originally Posted by AfricanHunter
18 1-2 sets with additional gears at $1095 plus lsd plus misc.
GT, where are you located? If we could get 18 paid commits, how long would it be to get first few boxes in and on the street?
Official ratios from Porsche: http://press.porsche.com/vehicles/20...pecs_Final.pdf
Left 981, Right 981S (=GT4)
That's 5.1% more torque to the wheels in 2nd gear. Will effectively raise 308ftlb to 324ftlb.
Also reduces top speed in 2nd gear by 4mph.
Even more improvement in 1st: 11% increase of torque to the wheel.
It almost seems that this is the transmission AP wanted to put in, but wasn't allowed to !
Ignore the torque to the wheel concept, it gives confusing intuition. Yes you have more wheel torque in "2nd gear", but you're also putting out that torque at a lower speed. What you care about is how much power you are putting out from the motor, and the lower 2nd just changes the speed range over which you have the most power available.
Ignore the torque to the wheel concept, it gives confusing intuition. Yes you have more wheel torque in "2nd gear", but you're also putting out that torque at a lower speed. What you care about is how much power you are putting out from the motor, and the lower 2nd just changes the speed range over which you have the most power available.
Taking it further, you need to look at the typical speeds at which you'll be shifting to determine the speed range and wheel torque you'll be experiencing in each gear. This is where the interaction of the gearing and the engine torque curve comes into play. I think the GT4 has a bit of a mismatch here for the road and, again, numerous other Porsches demonstrate that you can simultaneously have a good match for both road and track.
tis' simple but its' 10k more or less.
everying porsche is 10k here 10k there .
Tell me about it!!!! How about getting a used one (if we can find one)....you still have to open it put various gears in and the LSD might be a doable project...IMHO the custom 1-2 w/ mainshaft is a VERY long shot due to the economics of doing such a project....also like the idea of a spare transmission. Just found a few 981 2.7l on eBay in the $3k to $4k range....you will end up at $10k but that should be installed and you get to keep your OEM one.
Taking it further, you need to look at the typical speeds at which you'll be shifting to determine the speed range and wheel torque you'll be experiencing in each gear. This is where the interaction of the gearing and the engine torque curve comes into play. I think the GT4 has a bit of a mismatch here for the road and, again, numerous other Porsches demonstrate that you can simultaneously have a good match for both road and track.
I have long held the opinion that Porsche did it on purpose. They have never wanted the lowly Cayman/Boxster product line to equal the performance of the flagship Carrera model. They finally broke down and gave it the same basic engine in the GT4, so the only way left to keep it away from Carrera S performance was to hinder it with gear ratios.
As I have said previously, this gearbox is over a dozen years old. It was first designed and used in Audis. The original 987.1 gearbox actually has Audi 4 ring logos on it instead of the Porsche P in a triangle. It wasn't until 987.2 that it was a Porsche specific casting. Porsche had to chose the ratios since the TDi Audi ratios wouldn't work at all with the NA engine. When they chose those ratios, they obviously considered fuel economy balanced with performance, like they always do. I personally think that they deliberately gave it less performance than was possible for model hierarchy reasons.
I have long held the opinion that Porsche did it on purpose. They have never wanted the lowly Cayman/Boxster product line to equal the performance of the flagship Carrera model. They finally broke down and gave it the same basic engine in the GT4, so the only way left to keep it away from Carrera S performance was to hinder it with gear ratios.
As I have said previously, this gearbox is over a dozen years old. It was first designed and used in Audis. The original 987.1 gearbox actually has Audi 4 ring logos on it instead of the Porsche P in a triangle. It wasn't until 987.2 that it was a Porsche specific casting. Porsche had to chose the ratios since the TDi Audi ratios wouldn't work at all with the NA engine. When they chose those ratios, they obviously considered fuel economy balanced with performance, like they always do. I personally think that they deliberately gave it less performance than was possible for model hierarchy reasons.
My guess is that you're right. Even if its breathing is restricted, putting the 3.8 from the Carrera S into the GT4 should make the GT4 go like snot, and feel like it (as everyone expected). But it doesn't. Porsche surely knows that and how to fix it, and I doubt the cost of getting this right in the first place would have added much to the cost of the car, so I see only one possible conclusion remaining ...
Official ratios from Porsche: http://press.porsche.com/vehicles/20...pecs_Final.pdf
Left 981, Right 981S (=GT4)
That's 5.1% more torque to the wheels in 2nd gear. Will effectively raise 308ftlb to 324ftlb.
Also reduces top speed in 2nd gear by 4mph.
Even more improvement in 1st: 11% increase of torque to the wheel.
It almost seems that this is the transmission AP wanted to put in, but wasn't allowed to !
A slippiery slope if you start trying to say that the gear box will give more performance (overalll). it doesnt. HP does that......
remmber Acceleratrion = power / (mass x velocity) this means , simply (for performance) at any same , comparible speed, you want the greater power available.
So, what does this mean for gear boxes??? its all trade offs.. yes, as you say, you got 5.1% more torque in 2nd gear, But in shifting into 3rd, at 5.1% slower speed, you also got 25% less torque. until the old gear box 2nd would be at the same speed. in otherwords, you gain 5.1% more torque for the entire gear, but lose 25% torque for the speed you have to make up. the net net is a 0 sum gain! NO CHANGE overall. Now, i have to qualify that further by saying, "overall".. so, for specific speed ranges, yes, it can be a benefit. say, you were autocrossing and never got out of 2nd and the top speed of the original in 2nd was 5% too high for the car... then, it makes sense... your buddy on the track, was better optimized at one track with the new gear box, but the speed ranges at another track suites the original gear box better.............this is the logic you need to use when dealing with gears and ratios and their ability to put HP to the wheels.
Originally Posted by Mech33
Ignore the torque to the wheel concept, it gives confusing intuition. Yes you have more wheel torque in "2nd gear", but you're also putting out that torque at a lower speed. What you care about is how much power you are putting out from the motor, and the lower 2nd just changes the speed range over which you have the most power available.
yep...this is correct and you are spot on!!!! all trade offs with gears. no magic gear ratio here. the most important thing is keeping the engine in the sweet spot of the engine HP.. in the case of the GT4, its in the 5500 to 7700rpm range
Originally Posted by Manifold
Taking it further, you need to look at the typical speeds at which you'll be shifting to determine the speed range and wheel torque you'll be experiencing in each gear. This is where the interaction of the gearing and the engine torque curve comes into play. I think the GT4 has a bit of a mismatch here for the road and, again, numerous other Porsches demonstrate that you can simultaneously have a good match for both road and track.
dont confuse the enging torque curve with the engine HP curve. ...... you could care less about the engine torque curve as max rear wheel torue comes at the highest HP available at any given speed. i think you are on the right track looking it from the speed and output perspective though.
Originally Posted by GTgears
I have long held the opinion that Porsche did it on purpose. They have never wanted the lowly Cayman/Boxster product line to equal the performance of the flagship Carrera model. They finally broke down and gave it the same basic engine in the GT4, so the only way left to keep it away from Carrera S performance was to hinder it with gear ratios.
snip>>>>>they obviously considered fuel economy balanced with performance, like they always do. I personally think that they deliberately gave it less performance than was possible for model hierarchy reasons.
Matt, its an interesting theory, but there is no way porsche knows how most will be using the car.... of course, on the track you are wringing the engine RPM to redline and on the street not so much.. however actually the opposite happens here. the shorter gears of the GT4 vs the CS give it more of a feel of performance vs the taller gears.......why, well, for example, if you are driving around in 3rd gear at 40mph in the carrera S, the GT4 would be at that same speed at a higher RPM, with a feel of more power. (and actually more power at that speed truly) so, its possible that porshce with their vast racing knowledge , looked at alll the track work that they have seen and with the power rating of the GT4, maximized it for track use.. actually made it better. in seeing what ive seen of the GT4 at tracks, it seems like the gearing is optimize. its possible the gearing of the 991S is not as optimized for track use. its also possible that the 911 is more the gentleman sports car, more refined...more street use oriented and the GT4, by virtue of its name is more track geared (no pun intended) . the 7 speed allows for the car to operate at the higher freeway speeds with lower engine noise. the GT4 is missing that gear and that gear alone (with shorter gears).
I decided to pop back in for the benefit of the readers because there is a huge gap in Mark's understanding of the discussion and the point of my comment that he misquoted above several times in the conversation. Nobody said anything about making anything spin any faster. My comment was that a shorter gear or final drive will make more rotations. More rotations for the same distance, and that's why they wear out more quickly. The context was in response to Pete's question about longevity of a short ring and pinion option.
.
You are completely right....... yes, with a 4:0 vs a 3.8: or even a 2.2 :1 rear end, the pinion shaft will spin much faster, for a give RPM and road speed. BUT, is this really a concern.. have you ever seen a crown or pinion gear wear out on a Porsche? maybe you have. sure, ill have no issuses with that with my race car being 2.2:1, but is there really a different of wear with a 3.8 vs a 3.4 ring and pinon? sure the pinion will spin faster (5% faster) but is that really a concern?
sorry i misunderstood the point of your post at first.
Originally Posted by Mech33
Great post. Good to see others that realize it's all about power vs. speed in each gear. If another gear has higher power available at the current vehicle speed, then shift! Though in some cases on track I think there is more than just max power at every instant... sometimes it is thr controllability of a higher gear or the reduced number of shifts in a section that is a factor.
yes, this is the main objective of optimizing gears.. speed vs HP in each gear. for the street however, slightly different goals.. for me, as i mentioned, its about having the race gears in the 1-4 range and then to have a tall gear to keep hyway noise down with low RPM... efficiency is debatable by the way with lower RPM..that is not always the case. but i prefer to chug along at 2000rpm at 70mph if possible...
Matt, its an interesting theory, but there is no way porsche knows how most will be using the car.... of course, on the track you are wringing the engine RPM to redline and on the street not so much.. however actually the opposite happens here. the shorter gears of the GT4 vs the CS give it more of a feel of performance vs the taller gears.......why, well, for example, if you are driving around in 3rd gear at 40mph in the carrera S, the GT4 would be at that same speed at a higher RPM, with a feel of more power. (and actually more power at that speed truly) so, its possible that porshce with their vast racing knowledge , looked at alll the track work that they have seen and with the power rating of the GT4, maximized it for track use.. actually made it better. in seeing what ive seen of the GT4 at tracks, it seems like the gearing is optimize. its possible the gearing of the 991S is not as optimized for track use. its also possible that the 911 is more the gentleman sports car, more refined...more street use oriented and the GT4, by virtue of its name is more track geared (no pun intended) . the 7 speed allows for the car to operate at the higher freeway speeds with lower engine noise. the GT4 is missing that gear and that gear alone (with shorter gears).
Mark,
The gearbox has been using the same ratios since the 987.1 S engine. They didn't optimize anything for the GT4. They pulled from the parts bin. Though, as has been pointed out here, the 2.7 was given shorter ratios than the GT4. Don't confuse the GT4 with the Clubsport racecar. The Clubsport is a PDK and has very good ratios, ratios that are better optimized for the track.
You are completely right....... yes, with a 4:0 vs a 3.8: or even a 2.2 :1 rear end, the pinion shaft will spin much faster, for a give RPM and road speed. BUT, is this really a concern.. have you ever seen a crown or pinion gear wear out on a Porsche? maybe you have. sure, ill have no issuses with that with my race car being 2.2:1, but is there really a different of wear with a 3.8 vs a 3.4 ring and pinon? sure the pinion will spin faster (5% faster) but is that really a concern?
sorry i misunderstood the point of your post at first.
Yes, I see ring and pinions wear out all the time. In fact, until the GT4 3rd gear failures, it was ALWAYS the failure point on the Cayman racecars. And since Porsche won't sell you a ring and pinion, when it happens you have to buy a new gearbox. In the 996 and 997 Cup Cars a ring and pinion lasts about 80-100 hours. For the Club and GT3 Challenge and Pirelli Driver's Cup racers that's 2-3 years. In IMSA we generally replace them after Daytona and put the used one in the spares pile and can get most of the rest of a season out of a new one.
12-04-2016, 05:13 PM
