Hi

I'm confused and hope to get the views of the track gurus in the forum!

I've been told that the right way to double clutch on a downshift is as follows:
- clutch in,shift to neutral
- clutch out
- blip throttle to desired revs (with gear in neutral and clutch OUT)
- clutch in and shift to lower gear

I've also been told that the above procedure is for gearboxes without "synchromesh". For cars with synchros, the procedure is simply:
- clutch in, while moving lever to the lower gear, blip the throttle (with clutch in) to desired revs
- that's it!

Can anyone shed some light on which is the right way?
Is there any difference in revving the engine with clutch in, and clutch out but in neutral?
Will either method save wear on the clutch?
Will it unnecessarily wear the engine to rev with no gear engaged?

Thanks in advance!

Mike
90 C2

 

Both are correct.

The first proceedurre is what Skip Barber teaches, and you use in their school cars (The race series cars now have a sequential gearbox).

I did PDE last fall with a friend. Hurley Haywood was all over me because I was doing true double clutching. He said the syncro rings on street transmissions are strong enough that you only have to blip as you shift down - your second alternative. "Double clutching in newer cars is a waste of time." -- HH. (After double clutching for 4 years, it was tough to do a single clutch. My timing was all messed up for a few laps. BTW, with a sequential gear box you have to single clutch, it's impossible to double clutch)

I've read other race drivers who say it's not necessary, but they still do it because of the muscle memory/timing thing, and some of their race cars still need it.

If you check the archives, there have been a lot of threads with good links about this subject.

 

When I heel/toe, I typically use the first method you described because, at least in my C2, the gear slides in more smoothly. It may just be my gearbox though.

 

Strongly agree with the Hurley Haywood approach.
In cars with synchro's, only put the clutch pedal down once, blip high enough and early enough so you're still hard on the brakes when you let the clutch out, and make sure you have the clutch out before you start to turn the wheel. The latter advice is to asure no engine braking when you're actually turning. Making that mistake generally leads to a quick spin.
The Barber approach is "classical", but my instructor didn't even use it when racing. Modern race cars have no synchros, and are generally shifted without using the clutch. They let off the gas, brake(often left-footed), blip the throttle when the car's in neutral, and pull the lever for the downshift. In cars with a Jericho transmission, the technique can be mastered in one or two minutes.
In 964's, the brake/gas pedal allignment is poor and the blip technique on braking is easily accomplished only after you install a Wings pedal.Once you get the right pedal relationships, it's a snap. In most cars, you have to twist your foot so that your heel in closer to the gas pedal, while your foot covers the brake pedal. The Wings pedal makes that unnecessary, and you just slightly roll your foot, and catch the widened part of the pedal with the part of your shoe just ahead of the heel. Hope that helps. As
p.s.-I have no interest in Wings, just a satisfied customer.

 

Hi-
Could you provide a little more info on the Wings pedal? I searched the web and didn't find anything.
Thanks!
Jon

 

I never even knew what exatly heel toeing was. So what would you want to rev up to be for letting out

 

Johnf, nice gumby. Did you build that model 964?
I've been riding motorbikes for years (20) and I always rev the engine when changing down gears, it seemed to make the transition much smoother, and one cannot select neutral between gears so I always wondered if this was equivelant to double clutching in a car, now I know.
However, my 964 it a Tip so I don't need and cannot if I wanted double clutch.
Regards
Stephen Smith
93 C2 Tip <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

 

Wings Engineering is a group of engineers who race Porsches and make only one product for sale- a beautifully crafted pedal that is perfect for 964 Porsches. It installs in about 1 minute with just a Phillips screwdriver and no drilling.
Once you put it on, you wonder why Porsche didn't make it that way
Address is 54 Danbury Rd, Ridgefield, Ct 06877
Phone is 203-438-2222
Cost is $116 including shipping and is the best $116 you can spend on the car. AS
(No relationship to company-just a satisfied customer)

 

Richards 04- the idea is to rev enough to match the engine speed when you're shifting down. On the track, that's generally about 4000rpm. AS

 

Thanks Mike, Drew, Alex, Stephen

Tried both methods...the HH method seems to work pretty well for me.

 

I also have the "Wings technology" pedal installed in my 993, it works wonders in helping me with heel and toe.



FWIW, Porsche made "pedal" design changes with the 996 model cars.

I did find the "extended" version of the Wings technology pedal to be way too big, so I would recommend only the "standard" width version.

 

I was looking for something else in the two books I like for "advice from the top" on how to drive fast and well (believe me I need it - I seem to be able to drive fast or drive well but not both at the same time :-))

Anyhow here are Messrs Prost and Stewart on the subject:

Alain Prost – Competition Driving

Alain Prost: Technique of Double-declutching.
Along the straight, the accelerator is hard to the floor and the left foot is inactive on its aluminium rest (1). As the corner approaches, the right foot comes off the accelerator and begins to apply the brakes (2). Only now does the left foot come into action as the driver declutches, selects neutral and releases the clutch pedal once more (3). The right foot continues to brake, but the side of the same foot 'blips' the throttle to bring the engine up to optimum revs (4). The left foot again declutches, the required gear is selected, the left foot comes back off the clutch (S) and returns to its rest position. Once the double-declutching operation has been completed, the right foot continues to adjust the braking effort to obtain the ideal entry speed into the corner (6).
A simpler, pseudo form of double-declutching dispenses with the second declutching manoeuvre with the left foot. The 'blip' on the accelerator is given once the left foot on the clutch pedal has disengaged the clutch for the first time. Otherwise, the role of the right foot doesn't change.

Alain Prost: Should you double-declutch?
Generally when downchanging I go directly from the gear I'm in at the end of a straight to the one I need for the next corner: from sixth to second, for instance. I bypass all the gears in between. If it's sometimes possible to hear a couple of blips on the throttle, it's only during lengthy braking manoeuvres where for me it's a question of keeping the engine within the power band, rather than having to rev it at the moment where I would otherwise effectively need to double-declutch. I don't see the point in going right down through all the gears, but it's a question of whatever you yourself feel happiest doing, the main thing being to concentrate upon the braking when all's said and done. However, under hard braking or in the wet it's often worthwhile not to jump straight down the box in order to maintain the stability of the rear wheels.
As for double-declutching, it's something I do systematically, even if in a hurry it may seem brief, like a 'false' double-declutch. But I think it's essential you know how to do it. It won't matter over the course of a race; it will be more important over a whole season, and during the length of your career it will be invaluable. It's things like that that make you different from your team-mate and rivals: you miss fewer gears, do less damage to the gearbox, are a better driver for it and enjoy an enhanced reputation...

Jackie Stewart – Principles of Performance Driving
On the subject of gearchanging techniques, I have always believed that you should take as little out of the car's transmission as possible. That obviously means gentle, sympathetic changes when going up through the gears, but also using the brakes to their maximum when slowing down, often missing gears while changing down through the box. Many people think that racing drivers go all the way down through the gears in a six-speed box like a machine gun. But that means you're taking on a juggling act: steering, operating the pedals, blipping the throttle and using the gear lever like a madman (although the semiautomatic transmissions fitted to the current Williams, Ferrari and McLaren Grand Prix cars, with their steering wheel-mounted controls, make life rather easier for the driver).
I always chose to change down by jumping gears. I didn't in the early part of my career, but as I was able to develop more controlled pace into my driving I began changing from fifth to third to first or, in a six-speed box, from sixth to fourth to second. That applies to wet or dry conditions, although you need to be careful how you do it in the wet, perhaps eliminating all the downchanges, using the brakes to knock off your speed, and then finally slipping from sixth to first gear right at the end. Remember, you are not going to stop any faster by using the transmission. Brakes are made to stop a car, gears are primarily for acceleration. Deceleration was not part of the gearbox's original purpose; don't abuse it.
On the way up through the box you can also jump gears to beneficial effect, although the concept may sound rather strange. Coming out of Druids at Brands Hatch I would go directly from second to fourth gear. I was going downhill and I could not apply all the power in any case, because I would have to come off the throttle in third gear for Bottom Bend. Therefore, I would change slowly from second to fourth: it meant that the car would not accelerate so quickly in fourth gear, but it would be more settled in its attitude as I went through Bottom Bend and on that section of the track nobody could pass me anyway. This technique may have relatively few applications but there are some and it is worth bearing this in mind because the net result is to take less out of the car mechanically.
The other time I would change up early was on an undulating circuit, like the old Niirburgring or the original 'long' Oulton Park. Although I would be changing slightly before maximum revs, I might be going downhill: it was easier on the car. At the Niirburgring, I used to change up a gear when the car was in the air over the bumps.
A word about the 'heel and toe' technique for keeping the engine revving while you are shifting down through the gears. Heel-and-toeing never existed in the sense its name suggested: in real terms one just rolled the side of one's right foot off the brake pedal and blipped the throttle momentarily as required. Perhaps, way back in history, the initiator of this technique may have had a pedal configuration which literally required him to employ his heel and toe, but the practical reality of the concept today simply involves the side of the foot.
In order to be as easy on the car as possible, make it a general rule to try to run one gear higher than you initially think necessary. This also gives you more scope for improvement. If you are accelerating out of a corner in fourth gear, you may have a 500 rpm bank in which to improve the performance of that car before you change up. If you execute the corner outstandingly well, you might only have a 200 rpm margin through which to improve. But had you been in a higher gear there might have been 1000 rpm left: the car exits faster and receives less wear and tear. So, when you are able to change your gear ratios always try to select one ratio higher than you imagine you will need. If you have to back off the throttle for any reason when the engine is high in its rev range, the power transfer will be less marked if you are in a higher gear. The car will therefore be significantly less nervous to drive.

 

Boy, this discussion makes me feel old, even though I'm "only" 45!

Back in my early twenties, when I was an avid Formula Ford student racer at Jim Russell's Mont Tremblant school, the simplified double-clutch method was the only one being taught. Remember, these were old Lotus 69s and Van Diemen RF76s, all with Hewland 4-speed non-synchro gearboxes (ie. "crashboxes").

While blipping in neutral with the clutch pressed, one had to be very careful with the shift lever while releasing the clutch to ensure that the dogs of the two new gears meshed properly. If not, one "missed a shift" and the box popped back into neutral. Of course, it was just as easy to miss a shift going upwards, too!

Anyway, I had relatively few difficulties using this simplified method, and it has stayed with me to this day. Unfortunately, my new (to me) 964's pedals are, as someone put it, just not right for heel-and-toeing (very surprising to someone who expected racing perfection from a P-car). I believe I read somewhere that the brake pedal height is adjustable, and I will consider lowering the brake pedal an important and early modification on my car. It's not that the pedals are too far apart, it's just that the height difference between them is just too damn much!

<img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

 

I don't think the brake pedal is adjustable in the 91 964 (tho it certainly was on earlier 911's). In my experience, the blip/downshift technique is infinitely easier with the right pedal, and just about impossible without it. There are some cars like the Lotus Elise that make it easy right out of the box, some (Like my BMW850CSI) where it takes some practice, and some like the 91 964 where you just can't do it the way they made it.

 

I often perform doubleclutching on my 964 C4. I concluded that it's almost compulsory when gearbox is cold, and strongly advisable in town, especially when downshifting from 3rd to 2nd. I don't think it's so helpful in other cases. Doubleclutching on a synchromesh gearbox is useful only to preserve synchros and must be obviously performed quickly. Tazio Nuvolari was said to shift gears with doubleclutching faster than with actual sinchros!!
Comparison with motorbike riding can lead to error. When you accelerate in neutral with clutch engaged with a two stroke bike you just have to accelerate 2 or 4 small pistons, the same number of conrods, a lightweight crankshaft and lightweight gearbox stuff. On the 964 you must accelerate 6 big bore pistons, 6 conrods PLUS complete valvetrain PLUS truck-sized clutch plate PLUS the nice DMF, PLUS primary gearbox shaft. This just not to mention oil pump, powersteering pump and other auxiliary stuff. Even if you've got 250PS you can easily imagine how this stuff's inertia affects doubleclutching quickness.
In addiction if you don't match right RPM when downshifting at high engine load ( typically the engine runs faster than it should ) you give an impulse to the drivetrain which surely shortens Dual Mass Flywheel life ( which is already short enough! ).

Hope this may help.

However real doubleclutching is the first one mentioned in the first post. The other one simply accelerates the engine without accelerating gearbox primary shaft. It's surely less effective