That may be the consensus, but it's dead wrong.

If your technique and timing are any good, this is not needed. It also assumes that your gearbox is in good condition.

You generally raise the engine speed to a point above where it will need to be as the clutch is engaged. You are actually off of the throttle at the point of engagement. That's the reason the engine speed is initially higher - the engine speed will drop somewhat as you release the clutch pedal. There is no set rpm value - it depends on the engine speed before the change, the gearing on your car and how fast you make the shift.

The pedal arrangement on a 911 is not ideal and it does make it a little harder. You'll find it is easier on the track, as there you are on the brakes harder and the brake pedal is a little closer to the floor. There are things you can do to change the pedals but putting sandpaper on them isn't on my list of suggestions. That's a new one.

You can if you want. Done correctly it won't hurt anything. Few people do this...

JR

Right on!

If you heel and toe well you can release the clutch like a switch and the cars balance will not be disrupted in any way. Even on a 4th to 2nd shift from 110 to 40. Obviously I don't subscribe to the view that you should downshift one gear at a time.

first vid

Kelly in his C6 bodied 914 at IMR on Vimeo

listen around the :57 mark, you can hear the engine rev match, then clutch in - shift - clutch out is executed in the shortest possible time.

second vid

Poor downshift = a spin at IMR on Vimeo

you can hear the rev match, but timing is off, on releasing the clutch a small amount of traction was consumed as the engine and trans had to match and round we went!

There is way too much thought being put into this!!
Hands down the G-50 is one of the most straight forward (older) Porsche gearboxes.

There are really only three rules:
1. Be smooth
2. No slipping the clutch (unless you are starting in first gear from a stop)
3. Be smooth

If you simply concentrate on working any and all jerkyness out of your driving habits WITHOUT SLIPPING THE CLUTCH, then the proper technique will become evident. You will essentially teach yourself. have someone else drive it, or ride with you if you are not sure about the basics. It's hard to describe in the interwebs.

Here is a video of me learning the local track (HPT). The car is highly modified, but it still has a stock G50, stock sifter, and stock clutch.

I don't do any double clutching in this car. My previous 911 (an SC) did require some extra love to row through the gears.

<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/UU0zpSSItXg" frameborder="0" allowfullscreen></iframe>

Double clutching, rev-matching, heal-n-toe when street driving, totally unnecessary. Its built to funktion as a normal car! Track driving is another thing, but it's not necessary even then...

When to change gear, well it depends. When driving around the neighbors and in the city its fine to change at 3-3.500 and cruise av 2000. But when you want to it's totally OK to change gear at redline, its built for that too!

Then there is people that don't dare to rev the car above 4000, and I pity them, they are missing 90% of the cars!!

I think our definitions of "normal" driving must be a lot different. I agree regarding double clutching but rev-matching and heel-toeing makes spirited driving a lot smoother.

This is driving... if you own a 911 and cant do it learn how...even I have have pulled off a matched rev downshift...once or twice...:D

Not sure what you definition is. But if you feel that way you are probably driving too fast and to agressive for the the road. Take the car to a trackday, more fun and a lot more safe, both for you and those around you.


I find these "how to shift" threads entertaining, because you only find them on American Internet forums :)

Here's a video demonstrating heel-toe. The point of heel toe is to match the revs on downshift. This actually takes the synchro's completely out of the picture if you do it perfectly. Nobody does it perfectly - it isn't necessary since we have synchros. Closer is better.

I do this all the time. I've done it for 25 years. It's how I drive. I've never worn out a clutch and I've never had a problem with a 915 transaxle.

The factory gas pedal sucks. It's located too far below the level of the brake pedal. You can buy one of those fancy aluminum pedals to correct this. I did. I love it.

The factory was, as usual, more pragmatic and cheaper. They just bolt another stock pedal on top of the existing stock pedal. This double thickness is enough to correct the situation. I have no idea why they didn't get it right to start with. You'd think at some point in the 30 year run of the vehicle somebody would have suggested this as a potential area for improvement. Who knows...

H

To the OP, the timing of disengaging the clutch and applying throttle are no different than any other manual trans. ie- applying gas too soon in relation to releasing the clutch will result in slipping the clutch. So, don't over think this. Just drive and focus on shifting smoothly.

There is nothing that will wear out or get damaged in your trans by redlining first gear, provided you remember to let go of the throttle at the proper time and move it up a gear.

I'd not worry about double-clutching if you're not sure on when to apply throttle or let out the clutch-work on that timing first in moderate conditions before you get too crazy.

Yeah. And the thread should be retitled, "Proper way to shift a G50, Carrera 3.2"..... ;) I like your response, Mr. Hughes... :)

Technically, there is no advantage to matching the revs without double-clutching. True double-clutching includes a throttle blip while the transmission is in neutral, which spins the intermediate shaft up to meet the output shaft's rpm, thereby reducing the load on the syncros. Simply revving the motor while pressing in the clutch will only move the flywheel faster and reduce the mismatch between the pressure plate and the flywheel, which is not verysignificant, and those are two surfaces designed to rub each other. The key to syncro preservation is the rpm of the intermediate shaft within the tranny, and that can only be controlled with the engine when the clutch is engaged, and the tranny is in neutral.

My thoughts exactly. I don't understand the point of rev-matching and heel-and-toeing without double clutching. Once the skill is learned I don't think it requires any more time or effort and results in a smoother ride, in my opinion.

Geeze, I used to heel-toe my crappy little Nissan pickup even before all the syncro's died and it became a crash box (which REALLY taught me how to double clutch)...
(and the 63 Chevy pickup with 3 on the tree, the 76 Corrola 2 door, the 76 Chevy crewcab with the 454 and 4 speed w-unsynchronized granny low, and even the ancient Zellerbach Paper box-truck with 5 on the tree (I was the only person to ever find 3rd in it...), and every other manual trans vehicle I've driven since I was 17.)
Correctly matching revs saves the life of the transmission no matter what kind of stick you are driving and adds to the joy of driving correctly and neatly. (and it doesn't add to the effort of driving anymore then not scuffing your feet doesn't add to the effort of walking (while saving your shoes))


As far as non US forums not discussing shifting... Part of that is yes, you can find some discussion but to a larger degree it is because almost everyone there can drive a stick. You can't rent a stick from ANY major chain in the US because the vast majority of American drivers can only drive an automatic.
Look on a European rental car site and the base model car has a stick. Then as an example go on the US ebay site and try to find a Volvo with a stick. There are 300 Volvo's listed right now... 24 are manual transmission... subtract 2 commercial trucks and 11 cars from the 50s, 60s, and early 70s...
You are left with 11 Volvo sticks for sale with most of them in the east and only one in California.

So I think that maybe people in the US should discuss how to drive a stick and might have a tendency to need to learn about it. (Why are so many of the sticks in the northeast? Maybe snow forces people to really have to drive the whole car?)

(My more radical opinions include:
- The assertion that driving an automatic helps develop a mindset similar to aiming your couch down the road.
- That unless you can demonstrate a physical disability, that driving tests should be required to be taken in a car with a manual trans. (Drive the whole car don't just aim the thing!)
- That a car is a kinetic energy weapon and unless you treat it with seriousness like a loaded gun it cannot be safe.
- Driving a car is an art form and that a lot of joy can be extracted from doing little unnoticeable things well... such as shifting.)

Minor correction/side-note: I travel to Yurrup for business a bit. Almost all the cars you rent from Avis are manuals. In fact, it's very difficult to get an automatic. My boss doesn't drive a stick and he has to rent an auto. He has to go all the way to the largest car they have to get it. In fact, now that I think about it, maybe I don't drive a stick anymore when I go to Yurrup ;)

I think that's the essence of what he was trying to say.

I totally agree with your assessment about shifting and double-clutching. However, to be totally accurate, the input shaft is the element that is controlled by engine and throttle, with and without the clutch engaged, not the intermediate shaft.

The intermediate shaft has gears meshed with the output shaft > differential; so rotational speed is fixed via various gears meshing with output shaft speed and thus rotates with the drive wheels.

It is the rotational speed of the input shaft that must be controlled with the throttle with the clutch disengaged to smoothly mesh with the selected gear to downshift.

Some gearboxes shift so smoothly and effortlessly when new/nearly new that some owners feel double-clutching is no longer necessary. Nevertheless, they are a wear item. It just so happens the synchros on a 901/915 are more short-lived compared to more "modern" synchro designs. Owners who feel a throttle blip is all that's necessary will eventually understand the necessity of double-clutching and a well-padded bank account. In many cases, they'll sell the car before it gets to a critical point.

Many of those 2nd/3rd/4th owners are on this forum.

Sherwood

Blipping without the double clutch does help quite a bit. Do it and you can feel the reduced effort when you push it into gear. (Are you using your fingers instead of your fist?) Skipping the double clutch when blipping will speed up the shift quite a bit assuming that you have reasonably good syncros. You will put some wear on the syncros but no where near as much as just stirring the box.

So why does blipping do anything when you have released the pressure plate and the input shaft from the engine??

Because you haven't really released it...
That whole assembly isn't just coasting in there. When your clutch is released there are only a few thousandths of clearance in there. Air is a fluid and does have viscosity. Think Tesla turbine. The limit of blipping is that the efficiency of transmitted rotation to the free spinning disk drops like a rock as their rotation rates gets closer. That is why over blipping works pretty good and you'll see that lots of people get in that habit. It really shows when you have someone comfortable with the technique take their first crack at shifting a crash box.

If you have a driver that is reasonably good at just blipping their downshifts and they don't hurry their upshifts, I would expect their clutch to last 200k+ miles and their transmission to last at least 2 to 4 times that long. Remember that the syncros are simply a metal cone clutch so if you limit the speed differential and the force they are engaged at, it will reduce the wear accordingly.

------
Another detail:
I suspect when you are discussing double clutching you are only meaning on downshifts. If you have a car with a syncro-less gearbox then you have to double clutch upshifts too and it is a lot slower. (Yes lots of race boxes with no syncros don't require a double clutch on the upshift (or any clutch on the upshift) but they have lifespans measured in hours when used like that.)

I'm not sure you have a clear idea of what's happening inside a typical gearbox. All manual gearboxes have an input shaft, which takes power from the engine, then transfers it to various selectable gearsets to increase/decrease torque and speed. The power path from engine to input shaft separates via engagement/disengagement of the clutch mechanism. With the clutch disengaged (pedal down), there is no physical connection between engine and gearbox. Thus:

With the clutch disengaged, one can rev the engine until the cows come home, but there is NO effect on the input shaft or on any internal part of the gearbox. If you blip the throttle and you think it shifts better, that's independent of what's happening between the engine and the disconnected power path to/through the gearbox.

During normal shifting and/or with the clutch pedal depressed, the synchromesh assemblies perform the duty of matching the rotational speed of gear shafts. Hurray when they work as designed, and if they work as designed 20 years later, that's great, but YMMV depending on how the POs used/abused the synchros.

Downshifting requires the input shaft to speed up to bring the relative rotational speeds of the drive and driven gear shafts closer together (greater speed differential). This action must be performed by the synchros and/or assisted by double-clutching.

During upshifts, engine and input shaft speeds gradually decrease relative to increased output shaft and rear wheel speed (less speed differential). This action allows the parts to more easily match rotational speed without further driver intervention. However, if one were to totally isolate the input shaft (clutch depressed, gearbox in neutral), this would result in an input shaft speed of 0 rpm and require the synchro to work harder to match shaft speeds while selecting a higher gear ratio (less torque, more speed).

Manual gearboxes for race cars typically use straight cut gears and are easier to mesh w/o a synchromesh assembly. Road car transmissions typically use helical cut gears for greater tooth contact and are thus quieter but less easy to manually mesh, thus the need for a synchro. unit for each forward gear.

I hope this doesn't confuse too much.

Sherwood

The problem with the above bit that I've quoted is that it is all wrong except for the part about helical gears being used for road cars because they are quieter. (Listen to the rising scream of the wonderful straight cut gear noise as Hans Stuck tears up the Nordschleife in the M3 GTR.-> http://www.youtube.com/watch?v=eSi_nRSj5jM All that rising scream is straight cut gears.)
I'm left wondering how much you know about the inner workings of manual transmissions.
(As to quantity that I know: The first time I was asked by someone on another race team to rebuild and modify a transmission was in 1984. I have done a few... If you want to learn about transmissions I recommend opening a BW T40 or T50. You can completely disassemble one with nothing but a socket set and a heavy duty snapring plier.)

The ease of shifting a gear box isn't effected in the slightest bit by the difference in straight cut or helical cut gears because there hasn't been an automotive transmission in about 50 years that allows ANY of the gear faces to disengage in ANY fashion. The last box I'm aware of with a disengaging gear gearshift was a 3 speed box used in heavy duty Chevy and GMC pickups up to 1963. (Kind of odd box where the 1st/Reverse gate was actuated by sliding a floating gear around a helical splined center that was about 3" in diameter. I believe the twist of the splines was to cushion the gear contact when engaging by knocking back the sliding gear if there was relative movement.)

Modern automotive transmissions are all of constant mesh design. No portion of any gear face disengages unless the trans is disassembled. The only part that engages or disengages in any fashion is the slider over the splines set in the sides of the gear. Alternatively race transmissions sometimes use what is called a dog drive instead of splines. This as the advantage that once enough speed matching has taken place to allow any sort of engagement the taper of the dog teeth will suck the slider into full engagement where it will stay until the torque is released. Porsche 901-915 transmissions use what is commonly called a dog drive but it is really more of a really short spline.

The reason that race transmissions use straight cut gears is simple and it has nothing to do with shifting. It is simply because helical gears create a side load when force is passed through them. In other words: one gear tries to slide up its shaft while the opposing gear is forced down. At high force levels it is trying to tear the transmission apart. That is the only reason they are used. Period. (Ok, maybe the ease of designing/building one off or limited run straight cut gears is an added bonus...)

---
Back to the point which was blipping without double clutching...
- Try a 2nd to 1st downshift at higher rpms while holding the shift knob with only the tips of 3 fingers. Feel how much force is needed to press past the syncro engagement.
- Now try it exactly the same with a good aggressive throttle blip. You can clearly feel the reduced effort as you press against the syncros. It may not make sense to you but the effect is very real.

This is a much more obvious difference if you are trying this on a trans with a Borg Warner type cone syncro as any speed differential keeps the syncro blocking the slider's engagement. Thus the difference in force levels you can feel are much higher.
(The 915 and 901 syncros are more like the self energizing action of a standard drum brake and synchronization is more a matter of giving them enough time to do their job. )

To understand why blipping does effect the input shaft and counter shaft you really have to read up on Tesla turbines. The effect of the boundary layer friction is very real even if it counter intuitive. This effect is much stronger if you barely disengage the clutch which is how most people drive by reflex. If you push the pedal to the floor there is much less effect for the obvious reason that the wider gap massively reduces the boundary effect.

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The real effect we are left with is that a somewhat simple discussion has become WAY to confusing for Porsche 911 as he starts playing with the most educational car that is commonly available: The 89 and earlier aircooled 911. These cars will talk to you in ever increasing detail. If you actively concentrate on learning every time you get into one of these cars you will still have Aha! moments 5 years later as little details are revealed.