The PDK Is Not The Best-Performing Transmission They Could Have Put In The 991 Turbo

"colorfulyawn" (colorfulyawn)
05/14/2014 at 00:12 • Filed to: None

So, the popular argument among Porschephilles and fans of the latest thing would have you believe that Porsche is only offering the 991 Turbos and GT3s with their PDK gearbox because it is the absolute best-performing transmission they could put in their ultimate performance iterations of the 911, and no performance should be left on the table. On the surface, that's a fairly convincing position, considering that flappy paddle gearboxes do indeed outperform traditional manuals in most every contest of speed.

But it's wrong.

The PDK is not the best-performing transmission they could have used. A CVT is.

A CVT that could handle the torque of the Turbo engine would be the transmission that leaves absolutely zero performance on the table. With a CVT, you never have to shift because you're always in the perfect gear ratio and the engine can always be in the fattest part of its powerband. No wasted energy revving through the weaker parts of the powerband, and zero distraction from having to think about shifting. You just plant your foot and go.

If Porsche were serious about scraping every last bit of performance out of the jar, they would've spent the money they used developing the PDK on coming up with a CVT that can handle more than a Sentra's worth of power. But they didn't.

Why didn't they? Well, I don't work for Porsche, so I can't say for sure, but I suspect it's because the driving experience would be inconsistent with what its customers expect from a sporting vehicle, regardless of ultimate performance numbers. It's just not that much fun to pin the throttle and have the engine moan at a steady RPM as the car accelerates up to speed.

The PDK, then, is a compromise between performance and driving experience. Just like a manual gearbox is these days. It's just the compromise they were willing to accept. As are, apparently, most of their customers.

DISCUSSION (78)

Your boy, BJR > colorfulyawn
05/14/2014 at 00:14

I'd really like to kick you in the balls and set you on fire for making me say this, but shit man, you're right.

Manuél Ferrari > colorfulyawn
05/14/2014 at 00:14

Haha true.

I still dislike CVTs though :D

Arben72 > colorfulyawn
05/14/2014 at 00:17

I don't think it's possible to launch a cvt, but I could be wrong. That said, you can also say why didn't they develop a flying 911, instead of giving it better suspension. The technology isn't available for consumer use yet, same goes with a high torque cvt. That being said, taking the stick away from the gt3 (the turbo is a gran tourer so I'm ok with it being flappy paddles) is a crime.

Aaron James > colorfulyawn
05/14/2014 at 00:19

"A CVT that could handle the torque of the Turbo engine" simply doesn't exist so the PDK "is the absolute best-performing transmission they could put in their ultimate performance iterations of the 911"

colorfulyawn > Aaron James
05/14/2014 at 00:21

The PDK didn't exist either until Porsche developed it. They could have spent that effort on a CVT.

NinetyQ > colorfulyawn
05/14/2014 at 00:22

The technology isn't there for it, and neither is the demand I would guess. Also, a CVT would probably be significantly heavier than the PDK, which is part of why I'm guessing it's not used in Formula 1 either while flappy paddles are. F1 is all about performance (within the rules, obviously), so the fact that they, and every other racing series that I'm aware of, have not adopted CVTs indicates to me that either the technology isn't there or there are inherent limitations that would keep it from happening.

So we really can't blame Porsche at all. If anything, it's just the lack of a manual in the GT3 that we should bemoan.

colorfulyawn > Manuél Ferrari
05/14/2014 at 00:22

So do I.

I think I'd take one over an FPG, though. I'd take a slushbox over either.

Doug DeMuro > colorfulyawn
05/14/2014 at 00:22

Completely agree.

http://www.thetruthaboutcars.com/2013/07/in-def…

colorfulyawn > NinetyQ
05/14/2014 at 00:23

Actually, if I recall correctly, CVTs are banned in Formula 1. Otherwise, I'm sure they'd be using them now.

colorfulyawn > colorfulyawn
05/14/2014 at 00:24

Yep. Banned.

http://www.f1fanatic.co.uk/2007/05/03/ban…

beardsbynelly - Rikerbeard > colorfulyawn
05/14/2014 at 00:26

for a CVT to be the best performing transmission it needs to be able to perform first.

colorfulyawn > Your boy, BJR
05/14/2014 at 00:28

Yeah, I have that effect on people sometimes.

Alternator Fax > colorfulyawn
05/14/2014 at 00:29

A CVT has markedly more parasitic loss than a clutch based transmission and, unless it is physically very large, a CVT has a finite potential gear ratio range, both characteristics that have negative impacts on top speed.

colorfulyawn > beardsbynelly - Rikerbeard
05/14/2014 at 00:31

Which would've happened years ago had Williams' CVT not been banned from Formula 1 back in 2007.

I suspect Porsche has more money on-hand for developing their road cars than three F1 teams put together.

colorfulyawn > Alternator Fax
05/14/2014 at 00:32

Currently, yes. But not much development has been put into a performance-oriented CVT. It sounded like a good idea to the Williams F1 team, until the FIA banned it.

Aaron James > colorfulyawn
05/14/2014 at 00:35

Sorry, a rubber band will never be better than clutches and gears. You've obviously never driven a car with a CVT or you'd know they are terrible. They even put false shift points in some because people hate them so much. What could they possibly make the belt from for it to last 100k miles? Unobtanium is it for now.

Bob Loblaw Made Me Make a Phoney Phone Call to Edward Rooney > Aaron James
05/14/2014 at 00:39

Potentially good enough to be banned before seeing competition.

colorfulyawn > Aaron James
05/14/2014 at 00:40

I drove a rented Sentra with a CVT, and yes, it was pretty unfun to drive.

But it's pretty funny to put the shoe on the other foot and watch an FPG fan say the more advanced and better-performing option "will never be better than clutches and gears." Don't you know, that's the same argument you reject when it's coming from a manual gearbox fan.

Logansteno: Bought a VW? > colorfulyawn
05/14/2014 at 00:42

It pains me to say this... but I can't disagree.

Manuél Ferrari > colorfulyawn
05/14/2014 at 00:43

Haha why you hate flappy paddle gearboxes? They can be fun

Squid > colorfulyawn
05/14/2014 at 00:45

I guess you could be correct in the pure aspect of speed, but I don't know if the band would be able to tolerate that stress of engine braking going into a turn. But really you'd lose a satisfying BRAAAP! on the downshift. For pure straight line speed a CVT would net you impossibly sweet times, but I don't know that the band that is used on the cones would be able to handle the power with out losing massive amounts of power from slipping.

colorfulyawn > Manuél Ferrari
05/14/2014 at 00:47

Actually, yeah, they can be. If I were buying a car solely for track days, I wouldn't want anything but an FPG.

But I find them frustrating to drive on the street, mainly because of the way they take up the clutch when you start going. It's not so much the shifting I don't like giving up: it's clutch modulation. I can just do it smoother than any FPG can, and it feels a lot more natural to drive. That's why I'd even take a slushbox over an FPG, personally.

Aaron James > colorfulyawn
05/14/2014 at 00:48

I'm not a big fan of the FPG, It's Manual all the way for me. I'd take a 911 turbo with the PDK, but you couldn't pay me to DD a CVT car. the Maxima I drove was just gross, I hated it. CVTs belong on quads and that's it. I will admit it took me a while to be ok with FPGs.

NinetyQ > colorfulyawn
05/14/2014 at 00:48

What about other motorsports? My guess is that nobody uses it because of the droning engine noise that would occur.

colorfulyawn > Aaron James
05/14/2014 at 00:50

My apologies. I stand corrected.

Personally, I prefer a traditional manual gearbox too. My point in making this post is that the driving experience counts for something, and even Porsche isn't willing to completely throw it out the window for the sake of performance. But if they're already making performance compromises for the sake of driving experience, what's so wrong with wanting a different compromise in the form of a manual gearbox?

colorfulyawn > NinetyQ
05/14/2014 at 00:53

I'm not entirely sure, but the only racing series where I'd expect the development budgets to be anywhere close to F1 would be LeMans. For most motorsports, I suspect the cost of development is the prohibitive factor.

colorfulyawn > Squid
05/14/2014 at 00:56

I'm sure it would take some development, but then, so did the PDK.

But I will say that when a technology is banned from Formula 1, it's usually not because the FIA expects it not to work very well.

Leadbull > colorfulyawn
05/14/2014 at 01:02

They could never successfully market a 911 Turbo with a CVT.

colorfulyawn > Leadbull
05/14/2014 at 01:13

Yeah, probably not.

beardsbynelly - Rikerbeard > colorfulyawn
05/14/2014 at 01:15

Except that Audi are developing multitronic CVT's and they're part of VAG with Porsche. Currently the strongest CVT that I know of is the LuK/Audi chain driven unit that can handle 400 n-m of torque, far shy of the 911 Turbo's 650 n-m.

Just because Williams had their CVT in 93, doesn't mean that it was race ready or that no one else has been investing in research since then.

Manuél Ferrari > colorfulyawn
05/14/2014 at 01:24

Which DCTs have you driven?

The clutch modulation on the latest PDK is unreal. Sometimes you forgot it's not a slushbox.

colorfulyawn > Manuél Ferrari
05/14/2014 at 01:26

VW GTi, Ford Focus, and base 991 Carrera.

Manuél Ferrari > colorfulyawn
05/14/2014 at 01:28

Hmm, weird you didn't like the 991's PDK. I've driven one too and thought the clutch modulation was excellent.

colorfulyawn > Manuél Ferrari
05/14/2014 at 01:35

I have a close friend who is a Porsche tech, and he swears I'd like the PDK in the Panamera. So who knows, I may someday be converted. At least to the point where I might take one over a CVT, at least.

colorfulyawn > beardsbynelly - Rikerbeard
05/14/2014 at 01:38

I suspect Audi's CVT is developed more as an economical slushbox alternative, not a performance enhancer. Yet I don't doubt that VAG could develop a performance-oriented CVT for high-end sports cars.

Manuél Ferrari > colorfulyawn
05/14/2014 at 01:39

My old Man had a Panamera for about 3 years. The PDK was very smooth in it. I honestly forgot that it wasn't a regular automatic most of the time.

He got rid of the car not because of PDK but because of the AWD. He had one of the very first 4S cars sold in California and it was buggy. The front drivetrain created a faint but weird noise at highway speeds. Two different service centers tried and failed to fix the car. It was in and out of the shop for months at a time. When trying to fix the issue they created other issues and Porsche eventually bought the car back from him.

m2m, apex detective > colorfulyawn
05/14/2014 at 01:48

I will agree that a CVT could prove more efficient if it were more apt to be used with performance in mind. It would take all the fun out of driving, though; it's the going through the rev range we associate with acceleration ... but of course you know that.

So, while acknowledging that you might have a point, the MT might still be a good runner-up – and good enough for me.

Thinking about the SMG/PDK/CVT complex led me to believe that nobody is actually interested in achieving efficiency anyway.

beardsbynelly - Rikerbeard > colorfulyawn
05/14/2014 at 02:03

The limiting factor is currently the chain-belt. LuK make the strongest CVT chain belt on the market, designed with high-performance in mind (their words, according to their website ). They also supply belts to Subaru for their CVT's.

I think Jatco's CVT's in the Nissans are close behind but haven't cracked 400 n-m yet either. The largest motor they fit them to is the VQ35DE in the Murano and 350GT.

Sure, one day there'll be a CVT strong enough, but it's not for lack of trying that it isn't ready yet.

colorfulyawn > beardsbynelly - Rikerbeard
05/14/2014 at 02:06

I dunno, it was being developed for F1 more than 20 years ago. That leads me to believe it could be done now if it were a priority.

I'm certain they'd be common now if they hadn't been banned in F1. Might have even supplanted the development of FPGs.

colorfulyawn > m2m, apex detective
05/14/2014 at 02:12

I suspect that a lot of the reason FPGs are replacing manuals in ultra-high-perfomance cars like this has to do with emissions, not development costs or ultimate performance. With an FPG, the manufacturer has more control over how the car is driven by making gear changes consistent and super-quick.

Of course CVTs diminish the driving experience. So do FPGs, in my view.

D > colorfulyawn
05/14/2014 at 04:03

But look at it like this: the 991 isn't the fastest car Porsche is capable of making... So why bother squeezing every last drop of performance out of it... gotta leave some room for character

beardsbynelly - Rikerbeard > colorfulyawn
05/14/2014 at 06:50

unless of course, Williams tried to run it and found that it was unreliable and a waste of money. It's too hard to say, it was never race worthy.

pauljones > colorfulyawn
05/14/2014 at 10:36

Not necessarily; there are other reasons (though, admittedly, far less likely ones) that the CVT could have been banned. And while Williams might have had one they wanted to try in a race car, there was little data on the concept at the time. It may have made for a great racing transmission, but there's one thing that most people tend to overlook: engineering something for racing may be more fun and glamorous, but it is in no way harder to do than to engineer something for road-going cars. in fact, I'd argue it's easier. With race technology developments, you don't have to worry about budgets, mass production feasibility, material costs, etc. Even if it had worked in F1, there are a series of very daunting engineering feats that must be overcome for that technology to be viable outside of F1 racing. Issues with cost, complexity, and durability could very easily have stopped the notion of putting such transmissions in road cars sooner.

I don't know anything at all about the Williams CVT transmission, but I'd guess that the answer isn't quite as straightforward as saying that if Williams tried it 20 years ago, we're just to lazy or cheap to do it today.

m2m, apex detective > colorfulyawn
05/14/2014 at 10:39

Given that one of the most lauded automatic transmissions seems to be one of the current ZF 8ATs (though I forgot what car it's used in, but it was more than a few ... BMW 550i, maybe?). I'm sure they (ZF) would be willing to develop a performance CVT option if there were any takers.

Also, bluntly assuming that FPG stands for flappy, I'd say that they offer involvement if you can actually select the gear manually, both up and down; it should also avoid picking a higher gear just because you are close to redline.

Also, what's bad about up-up-down-down-style SMG 'boxes? Can't be that hard to get people to drive those, right?

colorfulyawn > m2m, apex detective
05/14/2014 at 10:52

Sure, I wouldn't say an FPG offers no involvement at all. It's a matter of degrees, in my opinion. A regular manual offers a little more, a slushbox a little less. Ultimately, my point here was that I wouldn't expect Porsche or it's customers to accept a CVT in its cars even though that technology is what would provide the absolute best performance, and that tech-loving FPG fans will most likely turn into the "Luddites" they accuse manual fans to be when a superior-performing technology supplants their favorite 'box.

colorfulyawn > pauljones
05/14/2014 at 10:58

Those are all good and valid points. I'd only say that we'll never really know for sure what would have happened because of the ban.

Personally, I think the easier development of racing parts is what helped the FPG become popular, and maybe if F1 hadn't banned CVTs, the benefit of that development time could have gone to them instead. But I might be wrong about that.

colorfulyawn > D
05/14/2014 at 11:00

That actually is exactly what my philosophy on the 911 is, only I'd use it to argue for a manual gearbox instead of the PDK.

colorfulyawn > beardsbynelly - Rikerbeard
05/14/2014 at 11:02

True, we 'll never know for sure. But I'd be surprised if developing automated manual gearboxes didn't present its share of challenges too.

fink stinger > colorfulyawn
05/14/2014 at 11:03

CVT can be very fun if done right.

Kinja'd!!!

colorfulyawn > pauljones
05/14/2014 at 11:07

oh, and I don't think it has anything to do with lazy or cheap. I think it has more to do with customers expectations of a sporting vehicle. Race cars have FPGs, so that makes them acceptable. Plus, you still get to climb through gears with them.

D > colorfulyawn
05/14/2014 at 12:26

Well I think it sure as hell is an argument against fitting it with a CVT

colorfulyawn > D
05/14/2014 at 12:35

Yes. I'm counting on it.

Cé hé sin > beardsbynelly - Rikerbeard
05/14/2014 at 16:57

Audi are getting rid of the CVT though aren't they?

TheCraigy > colorfulyawn
05/14/2014 at 18:22

There were other dual clutch systems on the market before PDK, including those suited to high-performance applications.

colorfulyawn > TheCraigy
05/14/2014 at 18:34

The point I was making was that nothing exists until somebody makes it, not that the PDK was the first gearbox of its kind.

osunick > Doug DeMuro
05/14/2014 at 19:11

Yeah, but Doug, the Prius isn't really a CVT in the traditional sense. The genius is the Prius doesn't really have a transmission at all- it has a planetary gear differential with an electric motor + ICE on one end and an electric motor + differential at the other end. Fewer than 10 moving parts. The Prius, for all its advanced engineering, is mechanically much simpler than a normal car.

Doug DeMuro > osunick
05/14/2014 at 19:15

Yeah, the Prius is a bad example.

beardsbynelly - Rikerbeard > Cé hé sin
05/15/2014 at 01:43

first I've heard, though wouldn't be surprised as they've been pretty unreliable.

beardsbynelly - Rikerbeard > colorfulyawn
05/15/2014 at 02:13

of course it did, but none of them limited by material strengths so much as the drive belt in a CVT.

probably won't matter too much in the future though anyway, electric motors make nearly all forms of transmissions obsolete.

colorfulyawn > beardsbynelly - Rikerbeard
05/15/2014 at 13:06

Yeah, the days of even worrying about gearboxes probably won't last too much longer.

wilderthanthehate > Aaron James
05/15/2014 at 13:48

they use steel belts, and they can't be rebuilt. a new nissan 'x-tronic' cvt is about 4000 usd. they are perfectly acceptable for a rental car (rented an altima with one, meh) but they just kind of suck for anything long term.

Mike_Smith > colorfulyawn
05/15/2014 at 17:21

But they already knew that steel gears could handle the torque, didn't they now.

Mike_Smith > colorfulyawn
05/15/2014 at 17:23

I'll bet you that if Porsche thought they could build a CVT that could handle the torque of a Turbo S, or a 918 Spyder, they would. Which leads me to believe that is not feasible with today's technology.

colorfulyawn > Mike_Smith
05/15/2014 at 17:24

The gears, maybe. It's not like there's never been a modern car in which the gears were a weak point, so I wouldn't consider that an absolute. And there are a lot more parts to the PDK than just the gears, quite a lot of them relatively new things. So what's the real difference?

colorfulyawn > Mike_Smith
05/15/2014 at 17:25

Perhaps. I suspect otherwise, though.

1337 MR2 > Aaron James
05/18/2014 at 18:36

Except in a halo car, an option high-po CVT would be acceptable to the hardest core enthusiasts. With turbos, imagine the SOUND a car like a 911 might make!

Aaron James > 1337 MR2
05/18/2014 at 18:58

it would be a horrible sound. Like when the kids rev their engines and keep them at redline. The entire time you were getting on it it would just scream at 8K rpm, no variation, no pops or gurgles. No thanks. Maybe someone would like that but not me.

poughdrew > colorfulyawn
05/18/2014 at 21:14

I also have it on good authority that the engine they used isn't the best performing because it's not a multi-stage rocket designed by cold war funded NASA.

Frobnoid > colorfulyawn
05/19/2014 at 16:15

Not being idiots, however, they chose to develop the PDK instead.

Ultimately, the CVT is not the answer — an all-electric powertrain is. Until then, all transmissions suck, whether PDK, CVT, manual, you name it. They all exist only because of a massive shortcoming with internal combustion engines. They are all compromises.

Frobnoid > colorfulyawn
05/19/2014 at 16:17

Man, I've got to believe the PDK 991 you drove had a problem.

Frobnoid > colorfulyawn
05/19/2014 at 16:21

But you can't wish things into existence, they have to be engineered. A CVT that would work well in a 911 Turbo is not currently feasible. Anyone trying to develop one is in a race against the day 10-20 years from now (if you believe Elon Musk) when electric cars start to dominate the market. Considering how long people have been trying to build decent CVTs, it just doesn't sound like a good use of R&D funds to keep trying.

Remember that PDK was developed by Porsche over 20 years ago, for racing. They didn't attempt to use it in street cars until it had undergone extensive refinement. These things don't get pulled out of somebody's hat.

colorfulyawn > Frobnoid
05/19/2014 at 17:42

All good points.

However, the question is why Porsche started developing the PDK 20 years ago for racing cars instead of a CVT? I'll speculate that the F1 ban affected manufacturers in other motorsports, and a fear of future bans led to the safer alternative of an automated manual. This would mean that the pinnacle of technology and performance weren't the ultimate goals in developing the PDK; staying within theoretical rule books would be a bigger motivator.

Who's to say that 20 years of developing a CVT instead of the PDK wouldn't have yielded something that would work in the Turbo today?

And how many enthusiasts would be happy about a 911 Turbo with a CVT, even if it crushed the performance of a PDK-equipped Turbo?

colorfulyawn > Frobnoid
05/19/2014 at 17:46

According to my Porsche technician friend, that's not out of the question.

Although the follow-up question I failed to ask was how many of the 7MTs have problems as well.

Wojtek > colorfulyawn
05/19/2014 at 18:20

They do not engineer their engines for the widest possible torque band just to kill the whole idea of using the variable revolution of the crank in function of vehicle speed. The idea of the CVT came from engines that worked with fixed RPM (possibly somewhere near the top torque value). A CVT works great as a transmission in this case. But what drivers are used to is applying throttle (more/less revs) in order to accelerate/decelerate the vehicle. Accidentally, from the packaging and engineering standpoint, this customer behaviour fits nicely with the idea of having a compact gearbox with a couple of fixed ratios and using variable RPMs of the engine. It's much easier to make the torque available in a wide RPM range than package a CVT capable of withstanding 600+ lbs/ft into a car. Not to mention the efficiency of a direct, fixed ratio gearbox (opposed to CVT). If it was that easy, compact and efficient, everybody would fit a hydraulic transmission (possibly with a sort of lockup) which acts like a CVT, has literally tons of torque capability and excellent, fine-grain control over the input-vs-output rev ratio. Problem is, such a hydraulic transmission weights half a tonne.

Frobnoid > colorfulyawn
05/19/2014 at 18:33

The hardware is very similar. As I understand it, the 7MT is just a PDK with manual actuators for the shifter and (single) clutch.

PDK is usually relatively bulletproof (witness the 911TT's ability to undergo successive launch-control starts until it runs out of gas or the driver gets bored.)

Frobnoid > colorfulyawn
05/19/2014 at 18:36

I imagine they were discouraged not only because of the racing regulations, but because so much engineering time had already been wasted by various manufacturers trying without success to build a good CVT for street use.

(Of course, it could be enlightening to see why F1 banned CVTs. If they were so problematic, why bother banning them, right?)

colorfulyawn > Frobnoid
05/19/2014 at 18:52

Indeed.

WarpSP > colorfulyawn
05/26/2014 at 12:58

Porsche didn't develope shite

Borg Warner in the USA developed the dual clutch trans!