[rottatate]

Inspired by the guy who lost to the Jag while shifting into second -

Every driving or racing video I watch, someone always comments on driver not knowing "how to shift, bro!" - and then they go on to say that if you practice enough then you can get perfectly smooth shifts in exactly 2 milliseconds every time. But I just don't understand how this is possible. Let me explain how I understand it, and let me know where I'm wrong.

Smooth shifts require rev matching. On downshifting this is done by blipping the throttle to match the engine to the wheel speed in the lower gear. When accelerating this is done by either waiting for the engine speed to come down so that it matches the wheel speed for the next gear up, or not waiting and letting the clutch out a bit early so that it slips and the friction helps bring the engine speed down. Double clutching can help bring the engine speed down faster, but you are still waiting until the rotational inertia of the engine and the flywheel is reduced the proper amount for the next gear. This is why getting a lighter flywheel can help. Correct?

Now, smooth shifting is not quick. Fast shifting requires releasing the clutch before the engine speed has come down to the point where it matches the wheel speed for the next gear. So the inertia of the engine is going to be transferred as a jolt or shock to the drive shaft, and the car will lurch forward (or the tires will break loose and chirp) especially when doing a quick shift or power shift. There is no way to avoid this jolt when accelerating quickly through the gears, right? You either let the engine slow (and it will be required to slow more the greater the gear ratio), or you get a nice kick to the rears. All of this is also going to wear down the drive train as well.

Let me know where I'm wrong here, I just can't understand how you could possibly achieve both a very fast and very smooth shift at the same time.

 

[UUUd444]

There are lots of videos around to help guys beat Jaguars by shifting quicker. Here's the first one that came up on a search and, being as how it's in a mustang, it's relevant.

https://ca.video.search.yahoo.com/s...67ae3f30138232852d401d46b4c20f2f&action=click

Pretty good video sound really demonstrates how the rpm climbs for a moment during a powershift between gears with the accelerator foot held to the floor. He'd for sure feel a bit of a jump as his clutch and trans catch up with his engine. Definitely a good idea to shift a bit before redline so you aren't bouncing off the rev limiter all the time though.

I'll bet his speed shifts feel almost perfectly smooth and seamless. And, he beat the Jaguar.

Sure, these shifts are harder on clutches and transmissions, but you have to give your synchros something to do or else why did you every buy them? In any case, three shifts in a side-by-side match up has to be only a fraction of what a clutch/trans goes through every time a person launches from stop.

If anyone ever actually waited for revs to drop and match or double clutched between shifts the jag wins every time, right? And we just can't have that, can we?

All the best. :bigthumbsup

 

[rottatate]

Thanks for the response! It's good to get some confirmation. The only thing you said that I don't know if I'm on board with is about his speed shifts being almost perfectly smooth - you can see in the video his 3-4 shift is a quick shift and there's definitely a jolt both times he does it. When I think smooth I think indistinguishable from an automatic, which is how I try to daily drive, but I think totally unachievable in a racing scenario. Which is all to be expected. There's a reason why lightened flywheels and engine cuts exist, right?

 

[Beechkid]

There is basically 3 styles of performance shifting techniques.....


Speed shifting- reving the engine up tight and without the clutch..only throttle use, slam the transmission up into the next gear----also known as Muroc


Power Shifting- Holds the clutch for a spilt second mid travel to allow 100% power delivered to the pavement by controlling wheel spin- yes, it is very effective but it eats clutches


and the 3rd....well, it's likely what everyone mostly does




BTW, what the kid in the vid is describing as Speed shifting- isn't................

 

[UUUd444]

There is basically 3 styles of performance shifting techniques.....

Speed shifting- reving the engine up tight and without the clutch..only throttle use, slam the transmission up into the next gear----also known as Muroc

Power Shifting- Holds the clutch for a spilt second mid travel to allow 100% power delivered to the pavement by controlling wheel spin- yes, it is very effective but it eats clutches and the 3rd....well, it's likely what everyone mostly does

BTW, what the kid in the vid is describing as Speed shifting- isn't................

I imagine there are different definitions in different places but what he called speed shifting was how I understood it (as it is referred to around here, anyway). I looked up the definition in Wikipedia and here's what they think:

Powershifting From Wikipedia, the free encyclopedia

This article is about the driving technique. For the book by Alvin Toffler, see Powershift: Knowledge, Wealth and Violence at the Edge of the 21st Century. For the PowerShift gearbox, see Ford PowerShift transmission. For the annual youth meeting, see Power Shift.
Powershifting, also known as full-throttle shifting or flat-shifting (not to be confused with speed-shifting), is a method of shifting used with manual transmissions to reduce the time where the driving wheels are not powered. Unlike a normal gearchange, in a powershift the driver does not let off the accelerator (unlike speed-shifting, where the throttle is let off very quickly, simultaneously depressing the clutch and shifting into the next gear, rapidly). The clutch is briefly depressed while the shift lever is rapidly shifted into a higher gear, keeping the engine in its power band. Keeping the engine in its powerband allows it to put down power quicker when the clutch is "dropped" and power returns to the transmission. In most cases, there is a method of cutting the ignition and/or fuel delivery, in a similar fashion to a rev-limiter, which prevents the engine from over-reving when the load from the transmission is removed. Many aftermarket[1] engine management systems provide this functionality as either a standard feature or as an option, usually combined with launch control.


In a situation requiring greater than usual acceleration I opt for the simultaneous gas off and clutch in for a split second as the shift knob is rammed into the next position. I'm afraid of the powershift as I want to protect the drivetrain as best I can within reason.


Does anyone know how much powershifting hurts our transmissions? Is there some automatic engine protection that doesn't involve rev limiter and possible oil pump gear damage? That would be great if there is.


That 'muroc' shift sounds like a bad idea for anyone without a really generous sponsor.


All the best.

 

[Grimbrand]

Let me put it this way. Proper powershifting can be done in a Toyota for many many years without significant damage. Maybe the clutch will wear out a little quicker. There's just not enough power for things to get hot enough to cause real problems.

In a V8 car with significant 'go', there are a few serious issues though, and reasons why it's mostly used on the dragstrip. One is that you're going to break the rear tires loose. Powershifting to do a really wicked burnout is ... well, it's the only way to get up in your gears without letting the back tires grab, unless you start in 2nd or 3rd. 3rd gear burnouts are sweet.

Your clutch will hate you. It's gonna heat things up significantly. If you can't throw the stick around with proper panache, in a rapid fashion, you are going to go up in revs too high, and that makes it worse...

But the worst is if you are more of a 'can't find 'em, grind em!' sort of person. If you can't get the 2-3 shift, you're going to overrev. Forget about getting it in gear now - if you don't have a rev limiter, you are going to get some free windows installed in your block.

So bottom line - if you are lightning fast with your shifts, and know your car well, you can powershift without really doing much harm except to the tires. Unless you have dogleg gears and are set up for clutchless shifting on the strip, this is the only way to fly. Full throttle the whole time, and keeping your RPMs high, letting your flywheel absorb (and deliver) the extra power during shifts.

If you're not so good at finding gears, powershifting will definitely trash your stuff.

Keep in mind, the meaner your engine and tire combo are, the harder this will be on everything, even if you're super fast. That's why racing parts are different and more expensive. =)


One last thing to mention: The really high-end rides don't usually powershift. Because it would break things. And because they need better, more consistent control so they don't just lay a 1/4 mile of smoke. Powershifting works best on cars that have enough traction not to just annihilate the tires, and helps you wring every last bit of power out of it in acceleration.

 

[Beechkid]

I imagine there are different definitions in different places but what he called speed shifting was how I understood it (as it is referred to around here, anyway). I looked up the definition in Wikipedia and here's what they think:

Powershifting From Wikipedia, the free encyclopedia

This article is about the driving technique. For the book by Alvin Toffler, see Powershift: Knowledge, Wealth and Violence at the Edge of the 21st Century. For the PowerShift gearbox, see Ford PowerShift transmission. For the annual youth meeting, see Power Shift.
Powershifting, also known as full-throttle shifting or flat-shifting (not to be confused with speed-shifting), is a method of shifting used with manual transmissions to reduce the time where the driving wheels are not powered. Unlike a normal gearchange, in a powershift the driver does not let off the accelerator (unlike speed-shifting, where the throttle is let off very quickly, simultaneously depressing the clutch and shifting into the next gear, rapidly). The clutch is briefly depressed while the shift lever is rapidly shifted into a higher gear, keeping the engine in its power band. Keeping the engine in its powerband allows it to put down power quicker when the clutch is "dropped" and power returns to the transmission. In most cases, there is a method of cutting the ignition and/or fuel delivery, in a similar fashion to a rev-limiter, which prevents the engine from over-reving when the load from the transmission is removed. Many aftermarket[1] engine management systems provide this functionality as either a standard feature or as an option, usually combined with launch control.


In a situation requiring greater than usual acceleration I opt for the simultaneous gas off and clutch in for a split second as the shift knob is rammed into the next position. I'm afraid of the powershift as I want to protect the drivetrain as best I can within reason.


Does anyone know how much powershifting hurts our transmissions? Is there some automatic engine protection that doesn't involve rev limiter and possible oil pump gear damage? That would be great if there is.


That 'muroc' shift sounds like a bad idea for anyone without a really generous sponsor.


All the best.

Alvin Toffler is a very typical "Expert" who takes what has been commonly known and done in the "real-world" and transforms it so one can sell books and argue they know it all....he has it completely backwards...........................

 

[JBert]

I pretty much agree with the OP -- you can have fast, or you can have smooth, but you can't have both at the same time.

To be perfectly smooth the revs must be matched to where they will land after the shift and to do this it takes some time.

To be really fast the revs will not be matched and something has to take up that shock. Personally I think the clutch is the best place to take it out since the clutch is sacrificial anyway . . . but slipping the clutch a little on each shift does take some time so we're back to the original contradiction.

 

[UUUd444]

Alvin Toffler is a very typical "Expert" who takes what has been commonly known and done in the "real-world" and transforms it so one can sell books and argue they know it all....he has it completely backwards...........................

I trust you a whole lot more than I trust Alvin what's his hat. So, in my mind, Alvin can beat it and keep his opinions to himself. I think I may have read somewhere that Alvin not only doesn't drive a mustang but he doesn't even know how to drive a standard trans. Geez...what a dink and a loser. Who does he think he is, anyway?

No offense intended for those mustang drivers who don't drive a standard transmission. That seems to be the rage now anyways and you are probably just ahead of the times (and, as usual, I'm behind). I guess I'm like many miserable old baxters. I kinda think my driving a manual shift mustang makes me less bland and more heroic. Please disregard anything I may have said earlier. (Not you, Alvin. Everyone else.)

Anyway, Beechkid, sorry for being such a dink and quoting Wikipedia who quoted Alvin. No offense intended at all. Really just trying to clarify it in my mind. (And then Alvin came along.)

All the best. sorry.gif