Any possible advantages of the 2.0 over the 2.5L ? - Page 7 - Porsche 718 Forum
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post #61 of 61 Old 03-28-2019, 01:13 PM
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A few additional thoughts. Claimer: I've been driving manual transmissions all my driving life, which is now over half a century. Disclaimer: I have not driven a 718 with 6MT and I DO love my 2.0L w/PDK. I tend to drive in Sport Mode most of the time except on the highway non-commuting. (Yes, it will go into 7th at 80mph, which I really ought not do so often except that people around me go even faster.) But I do know what all the discussion is about.

My observation is that the "lag" is not turbo boost at all. It is the wait from 1000rpm idle to the torque burst which begins at 2000rpm. With a manual clutch you (and I) would tend to rev the engine, probably above 2000rpm, just to get some angular momentum going. And with no load the engine rev's pretty quickly. When you release the clutch, not even popping it, you are transferring momentum to a stationary car. Since an IC engine has no torque at 0rpm, some slippage must occur as that momentum transfer happens.

With the PDK or any automatic, there isn't as much pre-build-up of rpm's to get angular momentum prior to engagement. So the initial burst from 0mph is less impulsive. Is it slower to get up to speed? Probably. Does it take more time to get to speed? Ah, that depends on when you start counting time.

With a manual transmission you generally start rev'ing as soon as you see that you can begin moving, but you don't actually start moving right away. When pulling out into traffic you can and probably do anticipate the coming opening and even start slipping the clutch a bit early, thus getting a jump on the launch. With the PDK you can't do that (well, almost, see below) because you'd start moving before the traffic opening gets to you. So in that scenario the 6MT is quicker to launch from a standstill once traffic allows. The total time between rev-start and any given speed in 1st gear is probably about the same as with the PDK, or perhaps a bit faster because the unloaded engine rev's so easily.

In a stoplight scenario where you can't anticipate the opportunity to go, you can't do much of the rev pre-build-up. You could have depressed the clutch and entered 1st gear but you can't do much else. So from stoplight-green to any given speed in 1st gear the two transmissions are more likely the same. The PDK is quicker to shift but first you have to get going fast enough to shift at all.

Now, there are exceptions to this simplistic analysis. The engine management is a little different, according to some things I've read. So the low rpm behavior might be better with the 6MT. (My recollection is that some part of the power or torque curve is lower with the 6MT, so maybe that's an intentional tradeoff. Or maybe it was to protect the clutch and gearbox. Whatever...) On the other hand, in the anticipate-a-traffic-opening scenario you can do some rev pre-build-up with the PDK but it requires both feet, holding the brake while you rev the engine. In other words, do "The Launch" thing. Most of us don't do that in normal traffic situations. When we can finally start moving we lift off the brake and depress the accelerator. (Back in the old days we were taught to use right foot for both because it prevents you from dragging the brake while driving. I wonder what most people do nowadays?)
ArchiProf, GregW, Chilli and 2 others like this.

Jim, on my second Porsche. The first was a 912 in a long time ago in a galaxy far, far away.

Last edited by jimmuller; 03-28-2019 at 06:41 PM. Reason: Always proofread to make sure you haven't a word out.
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