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Re: 6 speed tranny clearly enough...
^ Co-sign.
Gears are only there to keep the engine either in the
(1) In the sweet spot of the torque range.
(2) In the fuel efficient, cruising range.
F1 cars make pissloads of power but laughable torque - such is the reason they have 7 gears. I mean the cars weigh less than 1500lbs, the engines make 900hp+, and rev to the stratosphere but if you try to start out in 2nd gear you'll stall everytime!
Gears are only there to keep the engine either in the
(1) In the sweet spot of the torque range.
(2) In the fuel efficient, cruising range.
F1 cars make pissloads of power but laughable torque - such is the reason they have 7 gears. I mean the cars weigh less than 1500lbs, the engines make 900hp+, and rev to the stratosphere but if you try to start out in 2nd gear you'll stall everytime!
Re: 6 speed tranny clearly enough...
Heist, off topic, but last night they showed HEAT here on TV and immediately I thought of your posts.
As for six speeds being enough, there are now gearboxes with eight gears!
The new 997 makes top speed in sixth gear, seventh is for economy and relaxed cruising. I must say I kind of like that idea. In the regular 911 and with PDK, it makes sense. But in a GT3, I am very happy with having exactly six gears.
As for six speeds being enough, there are now gearboxes with eight gears!
The new 997 makes top speed in sixth gear, seventh is for economy and relaxed cruising. I must say I kind of like that idea. In the regular 911 and with PDK, it makes sense. But in a GT3, I am very happy with having exactly six gears.
Re: 6 speed tranny clearly enough...
Quote:
MarekN said:
The new 997 makes top speed in sixth gear, seventh is for economy and relaxed cruising. I must say I kind of like that idea. In the regular 911 and with PDK, it makes sense. But in a GT3, I am very happy with having exactly six gears.
You come around to my point. 6 gears are fine in a 997, and I agree that a 7th gear overdrive is good for long range cruising, which few 911s do, but I do.
Should PDK have 7 close-spaced cogs with top speed in 7th, I admit there might be a marginal acceleration advantage, but I think it's not worth the trouble.
To the replier who stated there are now 8-gear trannys, I say, more is not always better.
Re: 6 speed tranny clearly enough...
Retarded drawings to the rescue
Ok so first off hp is what decides how fast you accelerate. The short explanation is that, yes torque is a (twisting) force and torque matters, but it's torque actually at the wheels that matters and if you make torque at a higher rpm, then you can use a gear to get more torque at your wheels (think big lever with mechanical advantage). Guess what magical unit of measurement includes both torque and what rpm you make the torque... HP (hp = torque X rpm X a constant of proportionality). If this doesn't make sense learn more at your local internet.
So now that we know that keeping the highest hp is what really matters lets look at some dyno plots.
The first is a car that doesn't need a lot of gears. This is because the torque drops off quickly because this motor sucks and runs out of breath at high rpm. This creates a relatively flat HP curve because as torque goes down, rpm goes up and hp remains relatively the same. (BTW if you made 200 foot pounds of torque at 3000 rpm and 110 foot pounds of torque at 6000 rpm and at 30mph in gear A you're at 3000 rpm and in gear B you're at 6000 rpm, you accelerate faster at 6000 rpm with only 110 foot pounds of torque because gear B has a different mechanical advantage so that the torque at the wheels is greater since 110 is greater than half of 200 and 3000 is half of 6000). The point is with hp the same at all these rpms then you have an artificially wide powerband and you only need 5 gears.
Look at plot two, it's beautiful, like a GT3. It has a nice flat TORQUE curve. This is because for the particular engine size they made it work well at high rpms and low rpms. Again we didn't make it flat by cutting off the low end, we added high end with a motor that can breath. Only way to increase low end (on this optimized car) is add displacement. But we see now in this proper motor that we make so much more hp now at high rpm that we should take advantage of that and add gears. So really needing more gears is taking advantage of a car that can breath. It's not that these motors lack low end, it's that "torque motors" just don't have the high end they could potentially have. If you want more everywhere just build a bigger motor, that's a different discussion.
The second graph is not a peaky motor, it's just a good one that works well at all rpm (flat torque curve). The third graph is a peaky motor.
Finally, yes 7 gears would be nice on a 3. Many racecars and the extreme track day crowd use shorter 6 speeds that top out at 160 mph and they are faster because of it. If you had these 6 gears plus a 7th that topped out at 200mph for top speed (all 1-7 properly spaced without gaps), this would rock and be the best of both worlds.
Ok so first off hp is what decides how fast you accelerate. The short explanation is that, yes torque is a (twisting) force and torque matters, but it's torque actually at the wheels that matters and if you make torque at a higher rpm, then you can use a gear to get more torque at your wheels (think big lever with mechanical advantage). Guess what magical unit of measurement includes both torque and what rpm you make the torque... HP (hp = torque X rpm X a constant of proportionality). If this doesn't make sense learn more at your local internet.
So now that we know that keeping the highest hp is what really matters lets look at some dyno plots.
The first is a car that doesn't need a lot of gears. This is because the torque drops off quickly because this motor sucks and runs out of breath at high rpm. This creates a relatively flat HP curve because as torque goes down, rpm goes up and hp remains relatively the same. (BTW if you made 200 foot pounds of torque at 3000 rpm and 110 foot pounds of torque at 6000 rpm and at 30mph in gear A you're at 3000 rpm and in gear B you're at 6000 rpm, you accelerate faster at 6000 rpm with only 110 foot pounds of torque because gear B has a different mechanical advantage so that the torque at the wheels is greater since 110 is greater than half of 200 and 3000 is half of 6000). The point is with hp the same at all these rpms then you have an artificially wide powerband and you only need 5 gears.
Look at plot two, it's beautiful, like a GT3. It has a nice flat TORQUE curve. This is because for the particular engine size they made it work well at high rpms and low rpms. Again we didn't make it flat by cutting off the low end, we added high end with a motor that can breath. Only way to increase low end (on this optimized car) is add displacement. But we see now in this proper motor that we make so much more hp now at high rpm that we should take advantage of that and add gears. So really needing more gears is taking advantage of a car that can breath. It's not that these motors lack low end, it's that "torque motors" just don't have the high end they could potentially have. If you want more everywhere just build a bigger motor, that's a different discussion.
The second graph is not a peaky motor, it's just a good one that works well at all rpm (flat torque curve). The third graph is a peaky motor.
Finally, yes 7 gears would be nice on a 3. Many racecars and the extreme track day crowd use shorter 6 speeds that top out at 160 mph and they are faster because of it. If you had these 6 gears plus a 7th that topped out at 200mph for top speed (all 1-7 properly spaced without gaps), this would rock and be the best of both worlds.
Jun 16, 2008 9:24:15 PM
- connoisseur
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Re: 6 speed tranny clearly enough...
It seems to me that if manufacturers are requiring 7 & 8 speed greaboxes that it may be more fruitful to investigate the "automatic gearbox" that Jim Hall pioneered with the Chaparral. The advancements in computer control and hydraulics make such a device even more feasible. Manufacturers have forgotten the KISS principle. 
Jun 16, 2008 9:27:39 PM
- Moogle
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Jun 16, 2008 9:58:02 PM
- fritz
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Re: 6 speed tranny clearly enough...
Quote:
connoisseur said:
It seems to me that if manufacturers are requiring 7 & 8 speed greaboxes that it may be more fruitful to investigate the "automatic gearbox" that Jim Hall pioneered with the Chaparral. The advancements in computer control and hydraulics make such a device even more feasible. Manufacturers have forgotten the KISS principle.
Correct me if I am wrong, but wasn't Jim Hall's auto transmission just a conventional hydraulic torque converter and three-speed epicyclic transmission, but with the then innovative feature of a "lock-up" in the upper ratios?
If that was the case, then manufacturers did indeed adopt that concept and develop it further. See the Tiptronic, for instance.
Re: 6 speed tranny clearly enough...
I would definitely order the PDK if I were ordering a new 911, as the shifting is probably incredibly fast (much faster than me engaging a clutch and shift lever). Most of us are not Formula 1 drivers, and they have the advantage of the fast shifter.
My best guess is that Porsche waited this long to introduce the PDK for two reasons; 1) to make sure that they could patent critical parts of it; and, 2) to make sure it would work flawlessly - that is, a heck of a lot better than it does on most other cars (at least in the high end price spectrum) that offer a roughly similar option.
Jim
My best guess is that Porsche waited this long to introduce the PDK for two reasons; 1) to make sure that they could patent critical parts of it; and, 2) to make sure it would work flawlessly - that is, a heck of a lot better than it does on most other cars (at least in the high end price spectrum) that offer a roughly similar option.
Jim
Re: 6 speed tranny clearly enough...
New Honda/Acura NSX will need 8 forward gears to beat NBR time of GT-R:
http://www.edmunds.com/insideline/do/News/articleId=127306
http://www.edmunds.com/insideline/do/News/articleId=127306
Re: 6 speed tranny clearly enough...
One very interesting thing in both drive impressions in German mags AMS and AZ. They both claim that PDK is actually most natural in D mode(be it standard, Sport or Sport Plus). They even said that(my translation with little freedom)"..only shifting fan will use puddles since auto modes works almost perfectly!"...
Huh?!
Huh?!
Re: 6 speed tranny clearly enough...
Quote:
KresoF1 said:
One very interesting thing in both drive impressions in German mags AMS and AZ. They both claim that PDK is actually most natural in D mode(be it standard, Sport or Sport Plus). They even said that(my translation with little freedom)"..only shifting fan will use puddles since auto modes works almost perfectly!"...
Huh?!
PDK, the new Tiptronic, egnineered by Porsche.
Re: 6 speed tranny clearly enough...
Quote:
Jim48 said:
I would definitely order the PDK if I were ordering a new 911, as the shifting is probably incredibly fast (much faster than me engaging a clutch and shift lever). Most of us are not Formula 1 drivers, and they have the advantage of the fast shifter.
My best guess is that Porsche waited this long to introduce the PDK for two reasons; 1) to make sure that they could patent critical parts of it; and, 2) to make sure it would work flawlessly - that is, a heck of a lot better than it does on most other cars (at least in the high end price spectrum) that offer a roughly similar option.
Jim
Actually, they waited until they could redesign the engine, so they would not have the long distance with poorly supported shafts and clutches, going from the last main bearing to the first transmission bearing. Imagine the RMS problems then...
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