Porsche to include 7 speed manual option in new 911

[Allch Chcar]

Originally Posted by cyde01

never said that!

Oh really?

[cyde01]

of course a taller final drive would have better highway fuel economy, that's the laws of physics. i never stated anything to the contrary nor did i agree with anyone who stated that. if you thought that then you're missing the point of my posts entirely.

[Allch Chcar]

Originally Posted by cyde01

of course a taller final drive would have better highway fuel economy, that's the laws of physics. i never stated anything to the contrary nor did i agree with anyone who stated that. if you thought that then you're missing the point of my posts entirely.

I misread then, my bad.

[cyde01]

http://www.autoblog.com/2011/09/05/2...anual-gearbox/

As expected, engineers opted to use shorter ratios for gears one through six while leaving seventh gear nice and wide.

basically that's exactly what i said they were gonna do. like i said before, there's no point in keeping the same ratios as a 6 speed manual and simply tacking on a taller 7th gear. if you're gonna make a 7 speed, it makes a lot more sense if you use closer ratios for 1-6. what i'm concerned about is shift feel.

[serialk11r]

Hey guys I wanted to revive this discussion.

Do you guys think the manual transmission will live long enough to see the day when they are offered with 7 speed en masse? I feel like the answer is no because manual transmissions are a dying breed and it's hard to justify a new manual transmission design when it won't make money...

From a philosophical standpoint, more gears is better, but what do track guys think? Most 6 speed manuals are such that you are able to use 5 gears when wringing the engine out for max power, do you ever wish you had 6 shorter gears or closer gears to play with? I noticed that even on very "close ratio" transmissions, the gaps between 1-2 and 2-3 are often quite large and I imagine some acceleration could be gained from closer ratios. Changing out final drive can utilize the 6th gear for example, so I imagine some people would find more gears useful. With more focus on aerodynamics these days I imagine small sports cars could even start to hit higher speeds and get into 6th on a track.

Increased fuel economy standards are rolling in, and some cars are already extremely EPA test optimized, and are only barely hitting the requirements, so I imagine manufacturers will start getting either longer cruising gears or more gears into their manual transmissions and sporty/powerful cars to earn as many mpgs as possible.

[Levi]

7 gears are pointless IMO. I am glad the 981 has "only" 6. For me even five are enough for a sports car/track car.

[serialk11r]

Interesting (imho) you say that, because the PDK's 6th gear is only a tiny bit longer than the manual transmission's 5th, and the 7th is a very proper cruising gear, in fact on the Boxster (non S) it lowers the engine revs so much that the Porsche cruises at about 10% higher BMEP than the BRZ, if they had the same drag levels. Additionally, the PDK has much stronger acceleration off the line because the gears are shorter, and that would be a very tangible benefit in daily driving.

Not saying you're wrong or anything. Do you think the slightly increased shifting required would be annoying?

[serialk11r]

Any other track/racing guys have any comments on this?

[ZDan]

I don't know why, but when S2000 gearing is discussed, they only talk about the ratio of the particular gearset and NOT the ratio of engine speed to trans output speed, there's another gearset in there (input to layshaft? secondary output reduction? some such...)

If you look at the ratios including the gears between the transmission input and output, it's not a double overdrive.
AP1 5th and 6th = 1.125, 0.940
AP2 5th and 6th = 1.138, 0.931

6th is only *barely* overdrive.

Personally, I don't mind 4000rpm at 75mph.

The T56 in my RX-7, now *that's* a double overdrive: 0.74:1 5th, 0.50:1 6th.

[Ryephile]

Originally Posted by serialk11r

Any other track/racing guys have any comments on this?

I usually use 3rd to 5th on the track, since my torque band is flat from 5k-8200. Sometimes 2nd if there's a really slow [under 40 MPH] corner. I'd use 2nd to 5th more often if they were tighter, and add a 7th for Interstate cruising. That said, there are some close-ratio boxes that allow using more of the ratios. The downside is the car becomes useless on the highway because 6th is way too short. Again, 7 or 8 ratios would be nice.

FWIW, I instinctively tried to shift into 8th gear in my TDI this week. I'm so accustomed to putzing along at 1,200 rpm that once I got to highway speed [I'll admit I was chatting to the passenger meanwhile] that I saw my RPMs were at 2k so I naturally went for 2 more ratios up, which would've been 8th. Strangely enough, I ended up back in 6th. I need an 8MT ASAP.

[serialk11r]

Originally Posted by ZDan

I don't know why, but when S2000 gearing is discussed, they only talk about the ratio of the particular gearset and NOT the ratio of engine speed to trans output speed, there's another gearset in there (input to layshaft? secondary output reduction? some such...)

Yea, I don't know why people talk about "overdrives" even, it doesn't matter if the ratio is >1 or <1, it matters what the ratio between the ratios are, and the engine speed vs. vehicle speed/wheel speed.

The S2000 has extremely close ratio gears though, and I imagine with a higher final drive 6th gear becomes useful on the track, is this the case?

Originally Posted by Ryephile

I usually use 3rd to 5th on the track, since my torque band is flat from 5k-8200. Sometimes 2nd if there's a really slow [under 40 MPH] corner. I'd use 2nd to 5th more often if they were tighter, and add a 7th for Interstate cruising. That said, there are some close-ratio boxes that allow using more of the ratios. The downside is the car becomes useless on the highway because 6th is way too short. Again, 7 or 8 ratios would be nice.

FWIW, I instinctively tried to shift into 8th gear in my TDI this week. I'm so accustomed to putzing along at 1,200 rpm that once I got to highway speed [I'll admit I was chatting to the passenger meanwhile] that I saw my RPMs were at 2k so I naturally went for 2 more ratios up, which would've been 8th. Strangely enough, I ended up back in 6th. I need an 8MT ASAP.

Wait 5k? I guess that's 2nd gear, 2-3 lands you at 6140 shifting at 8500.
Hmm gonna run some quick numbers, at 6140 you have about 70% of peak power. 3-4 lands you at about 6700, where you have ~88% peak power.

So the stock transmission's ratio between the gears are 0.658, 0.722, 0.787, 0.786, 0.890 (wtf??). 1st to 6th is then 0.2616. If we shrink 6th down to about where 5th used to be, 7th can be at a comfortable 0.6-0.7 or so without too big of an rpm drop, and give excellent fuel economy on the highway. 3.4 2.4 (0-60 be damned) 1.85 1.44 1.13 0.90 0.65 which gives 0.706, 0.771, 0.778, 0.785, 0.796 between the first 6 gears, so that you always have about 7/8 of peak power between gears 2-6. 7th gear is actually just 0.722 away though, so that's a pretty synchro friendly shift. With the same final drive top speed would be a little higher and fuel economy would be something like 10-20% better depending on speed.

What car did you drive that had 8 gears? :O

[Levi]

Porsche 991 / Porsche 981
3.4l H6
350 PS @ 7.400 RPM / 315 PS @ 6.700 RPM
390 Nm @ 5.000 RPM / 360 Nm @ 4.500-5.800 RPM
1.380 kg / 1320 kg
0.29 Cw / 0.31 Cw
7MT / 6MT
0-100 km/h: 4.8 sec / 5.1 sec
0-160 km/h: 10.4 sec / 11.0 sec
80-120 km/h (5th gear): 6.4 sec / 6.7 sec



Unfortunately I can't find data of gear ratios. So I can't make any sense. However I think, if both cars were the same with the same engine, one 6MT and the other 7MT, maybe the 7 speed gearbox could have better overall poerformance, but it would still not be better than a true 7 speed dual clutch. So ofr performance I'd pick PDK/DKG/DCT, but as manual I'd keep it simple with a 5 speed or 6 speed for higher top speed.

[serialk11r]

Of course it wouldn't have better performance than any kind of automated shifting box, but higher top speed? More gears makes getting a higher top speed easier since you don't need to compromise the 6th gear (especially on a powerful car) for fuel economy.