As I understand it, it means shifting without using the clutch. But I don't see how this is possible...without leaving your tranny on the road in the process. I hear alot of Mustang and F-body people do this at the strip. I'm not trying to emulate, just clarify. Thanks. Oh yeah, and it benifits how?
11-01-2000, 12:11 PM
The benefits that I see are to be able to get on the power sooner after the shift and also to keep the boost up in between shifts. I was reluctant to try it at first, but it doesn't seem that bad on the car. It might wear the clutch a hair more but no worse than a hard launch.
11-01-2000, 12:13 PM
Power shifting is shifting without letting off the gas, you stay in the power.
Speed shifting is shifting and "very quickly" letting off the gas and back into it.
May help a little if you're drag racing, like worth a tenth or two? Prob not worth it unless you're pretty hardcore.
You can shift without the clutch, but it's pretty tough to do it faster than powershifting in a street car. You need to double-clutch and/or rev match to get it right. I've read that some race car drivers will do clutchless shifts so they can use their other foot for braking or whatever, but they also have pretty beefy trannys in a full on race car.
11-01-2000, 12:16 PM
Seems like it'd be a good way to fry your clutch and maybe even the engine. I'm shifting at 6500rpm and you want me to <b>keep</b> my foot on the gas while I depress the clutch. No way! I'd be bouncing off the rev-limiter instantly, then would be slipping the clutch while/when I let it out. I just don't get it.
11-01-2000, 12:18 PM
as in F1 and CART, and the Ferrari paddle system.
11-01-2000, 12:57 PM
Speed shifting - shifting without lifting throttle and fully disengage clutch.
Power shifting - shifting without lifting throttle and partly disengage clutch.
IMHO speed shifting is not that hard on the car but power shifting puts a lot of wear and tear on the synchros.
11-01-2000, 02:32 PM
11-01-2000, 07:05 PM
11-01-2000, 07:59 PM
You won't fry your clutch. Besides it's all under warranty. =)
11-02-2000, 04:27 AM
to maximize acceleration. If you shift quick enough you'll never touch the rev limitor or even get into the red zone. I agree it adds wear and tear on the drivetrain but it won't be any worse than a hard launch. Occationally doning this for a drag run should be fine.
11-02-2000, 05:01 AM
11-02-2000, 06:19 AM
11-02-2000, 08:17 AM
11-02-2000, 10:17 AM
There is absolutely no way you won't bounce off the limiter when powershifting. A typical performance engine will likely be gaining rpm at a rate of around 10,000 rpm per second at the shift point with clutch disengaged (much more than that at the torque peak), and a typical synchro in a "performance" gearbox won't allow engagement for at least 15 hundredths of a second - assuming the driver can execute that quickly, which is doubtful. Do the arithmetic.
Powershifting is very hard on synchros, plus the rest of the gearbox, the clutch, and the rest of the driveline, for that matter. The reason you do it is to take advantage of the inertia of the engine, engine accessories, flywheel, clutch and transmission input shaft to deliver a torque spike to the drive wheels, thus giving you a lunge you wouldn't get by shifting normally. I.E. - If you shift an A6 2.7T from first to second at 6500 rpm while lifting off the gas, the engine will lose, say, 200 rpm during the shift, and will get to about 3500 rpm in second, thus delivering a 2800 rpm "spike" to the wheels at clutch release. Powershifting at the same rpm with a 7000 rpm limiter, you'll deliver a 3500 rpm spike to the drivewheels, making for a bigger lunge at clutch release. That same torque spike is also delivering a blow to all the driveline components, however, plus you are definitely hitting the rev limiter while shifting, regardless of what a lazy tach mechanism may indicate.
Powershifting is hard on the engine, clutch and driveline, but it's also very rewarding when executed properly - especially on a turbo car, which will have essentially no turbo lag in the next gear.
11-02-2000, 10:29 AM
I agree it's hard to shift quick enough not to bounce off the rev limitor on most cars. But on the 1.8t I make my 2nd to 3rd and 3rd to 4th shifts at 5500rpm. I don't know about power shifting but when I speed shift I never hit the rev limitor in 2nd to 3rd and 3rd to 4th shift I don't even hit the redline. 1st to 2nd on the other hand is impossible not to hit the rev limitor therefor I shift normally on that one. I find the 1.8t has relatively slow throttle responce compared to some other cars.
I guess when power shifting the shifts can't be executed quick enough compared to speed shifting because of the additional load on the synchros. Am I right?
11-02-2000, 03:08 PM
If voting could change anything it would be made illegal.
11-02-2000, 04:57 PM
11-03-2000, 06:57 AM
""I agree it's hard to shift quick enough not to bounce off the rev limitor on most cars. But on the 1.8t I make my 2nd to 3rd and 3rd to 4th shifts at 5500rpm. I don't know about power shifting but when I speed shift I never hit the rev limitor in 2nd to 3rd and 3rd to 4th shift I don't even hit the redline.""
I'm assuming your reference to speedshifting is according to your previous definition - that is, full clutch release under full throttle. I refer to any full throttle shift as a powershift, but under your definition, a speedshift will allow more rpm gain than a powershift. From my point of view, they're nearly indistinguishable, primarily because of normal synchro limits on a street gearbox.
If you aren't hitting the rev limiter during *any* powershift, Butch Leal (or maybe Ronnie Sox) may have to step down from their thrones and place the "Fastest Shift Man on Earth" crown on *your* head. :-)
Let's say you can complete a shift in two tenths of a second, measured from clutch release to clutch engagement (I.E. - pressure plate and disc in contact, with full pressure, rpm beginning to drop). Two tenths for a shift is *very* fast. Trust me.
At a conservative minimum, your engine picks up 2000 rpm during that two tenths of a second. I'd be willing to bet that a low-inertia motor like a 1.8T will pick up more than that, but I'll stick with 10,000 rpm per second at the shift point. So if you're shifting at 5500 rpm, your engine is hitting 7500 rpm during the shift, unless the rev limiter intercedes.
Your eyes and ears - AND your tachometer - are not reliable guides as to whether or not you're hitting the limiter. Your tachometer isn't fast enough to show this nearly instantaneous rpm change, and you're busy enough at the time so that aural feedback from the engine will not be significant, either. We're talking a small fraction of a second, here, plus today's relatively soft limiters will not give feedback unless you're on the floor, *in gear*, when you run up against it.
As an anecdote, I was running an LT1 Corvette a few years back, and when powershfiting, the tach needle would barely move. Made me proud. :-) When I installed a Hypertech chip, the car would suddenly get really squirrelly on the one-two shift when using the same 5500 rpm shift point. My initial thought was "Wow, what power!", but with ETs and speeds barely improved, that clearly wasn't the case. The reason that the car would break loose so badly with the Hypertech was that they raised the rev limiter from 5850 to 6200 rpm. On a stick LT1 Vette, doing the one-two at 5500 rpm gets you to 3700 rpm in second gear, so when powershifting, the engine hits 5850 just before it gets dragged back to a theoretical 3700 rpm, therefore hitting the drive wheels with a 2150 rpm torque spike. With the Hypertech, I was getting a 2500 rpm torque spike. The obvious solution was to raise the shift point to about 6000 rpm, thus restoring traction after the shift (6200 - 4030 [rpm after shift] equals 2170 rpm, about the same as before the chip).
(Note that you'll never get back to the calculated rpm after a powershift, since the torque spike drags car speed up.)
The point behind all this verbosity is that I was hitting the limiter, with absolutely no clue that it was happening. That led me to do some research, some of the results of which you are now reading.
Maybe a VAG tool can confirm what I'm telling you.
""I find the 1.8t has relatively slow throttle responce compared to some other cars.""
Throttle response has nothing to do with it. You're already at full throttle and have been there awhile, so the engine will do its best to rev its little heart out, when effectively at full throttle in neutral.
""I guess when power shifting the shifts can't be executed quick enough compared to speed shifting because of the additional load on the synchros. Am I right?""
The synchros will do their best, regardless. On a street gearbox with synchros, there is only so much you can do, period. Before, I said 15 hundredths was the limit, but that may in fact be expecting a little too much.
When campaigning that Vette (I was on a quest from God to get the quickest ET on the planet from a 100% stock six-speed LT1), I did some sound recordings, and analyzed them on a PC. On several examples, I was able to get down to two tenths of a second (or a tad less) for a shift, based on my analysis of the sound - and as near as I could tell (not 100% reliable, as it involved some judgement). Let me tell you, those shifts sounded really *good*. In fact, they were hardly perceptible, and would just make me grin as I listened. No brag, here. I was on a quest from God. :-) More importantly, there was absolutely no aural indication that I was hitting the limiter during the shift - which I most certainly was.