911pcars

Since this is the Racing forum, we must remember that racers usually have a budget for scheduled gearbox rebuilding. Thus, if your are one, shift in any manner that decreases lap times.

Driving a piece of transportation, for most people, requires some restraint in the way pieces of a car (like a gearbox) are used. So in this environment, it's always better to not speedshift and to double-clutch so the equipment lasts longer. Or.... you take your racing or recreation budget and plug it into periodic synchro replacement.

MHO,
Sherwood

InThePocket

Wow, that video is fascinating Geza. I've not seen an example like that. Thanks for posting. I wish I could slow it down a bit, remove his right arm, and see the shifter better. It appears he never really lets the clutch pedal out completely. How long before the clutch goes?

Roger

TD in DC

Thanks! That is a great example. I have been practicing for a couple of days now, and it is getting much easier, and I am far better at downshifting smoothly.

Geo

Oh please.

My last two road cars before my BMW were a Sentra SE-R with a 200 bhp NA engine and just under 200k miles and a turbo G20 with just over 200k miles. Heel/toed both, single clutch, all the time. Never a problem with the synchros with either.

This is silly.

38D

I think between me and the PO, we did nearly 10 years of track driving in my old 914/6 with a high HP 3.2 (and it was a 901 gearbox, which ain't exactly strong). Synchros will last plenty long even on the track, so long as you don't try to rush the engagement.

Bull

I agree with 38D and George. Porsche syncros last a loooong time IF NOT ABUSED....and single clutching is not abuse! I have owned just about every 911 trans from the 901 forward, and many of each, with high mileage and heavily tracked cars. The syncros were the least/last of my concerns.

kurt M

I understand the activities going on in the gear box and am not one to underestimate a pro driver.
When the input shaft is kept at motor speed during the brake phase (clutch engaged) you can select and shift to a lower gear by rev matching the motor as the output shaft is moving at relative wheel speed and the input shaft will be naturally matching up as the correct lower gear is selected. The delta will be in motor speed from the higher gear to the lower gear. (Why we shift in the first place) The delta is motor speed if done a the right time and the syncros are not stressed if the lower gear selected is in range. in fact as I am sure you know you can shift a syncro box via dog box method with rev matching alone, if done precisely. It is fun to learn interesting methods as there are many feet, many variables and many ways to do things!

911pcars

"Oh please.

My last two road cars before my BMW were a Sentra SE-R with a 200 bhp NA engine and just under 200k miles and a turbo G20 with just over 200k miles. Heel/toed both, single clutch, all the time. Never a problem with the synchros with either.

This is silly."

Silly?
In the appropriate BMW/Nissan/944 forum, your observation maybe quite valid. However, I was referring to a 911 and specifically the 915 gearbox, not a G50 or Aisen or Getrag. Perhaps I should have qualified my previous statement. IMHO, you're attempting to compare apples and oranges.

"I think between me and the PO, we did nearly 10 years of track driving in my old 914/6 with a high HP 3.2 (and it was a 901 gearbox, which ain't exactly strong). Synchros will last plenty long even on the track, so long as you don't try to rush the engagement."

Based on your experience, synchro wear was of little consequence in your 10 year old track car. That's great, but how does that equate to street-driven cars that are around 30 years old and have >100k+ miles on the original drivetrain? How many more up and down shifts is that?

".....Porsche syncros last a loooong time IF NOT ABUSED....and single clutching is not abuse!..."

What is a loooong time? Would that be 20 years or 125k miles whichever comes first? You are shifting the gearbox as designed. I agree. Using it in this manner is not abuse. However, in the process of speed-matching, the synchro assembly is being worn (it is a wear item). The greater the speed differential before meshing, the greater the wear. The smaller the speed difference before meshing, the less wear. With a mixture of stop and go, cruising and banzai driving conditions, I fail to understand "no wear" using the single declutch method.

This is the race car forum and I wanted to separate that aspect of driving style with comments from non-track car owners. As with most things and especially with this thread, YMMV.

Sherwood

Geza

I'm not quite sure I follow what you are saying. Rev matching the motor with the clutch engaged (depressed) will not affect the speed of the input shaft, as the input shaft would be disconnected from the engine and would be spinning at a speed dictated by the wheel speed and the current gear selection. Shifting to a lower gear at this point would require the syncros to speed up the input shaft (still disconnected from the engine) to the proper mating speed for the lower gear. As long as the clutch is depressed, engine speed has no affect on the input shaft speed...they are completely disconnected. Please correct me if my understanding of what you stated is wrong.

Now, if you use (what I believe is) the method you described without the clutch and shift into neutral, blip the throttle to rev match and then shift from neutral into the lower gear, you've basically done a DDC without using the clutch. That'll work, but will probably lead to greater instability in the braking zone or at turn-in.

General comment:

Everytime this subject comes up, I find two types of people emerge. Those that want to learn it, because it is another skill set to learn to become a better driver, and those who argue that it is not necessary with modern gearboxes. True, it isn't really necessary, but, I'm with the first group. Sometimes I think the later group uses their argument to justify the fact that they haven't mastered the technique...just my GENERAL observation.

Geo

Well, if you're being specific, you should specify what you're writing about from the get go and not write generally.

Oh come on.....

First you say periodic maintenance and then you reveal you're talking about a 30 year old car.

kurt M

Geza, don't get me wrong! I am in the learn it, understand it camp 100%. I also like to spilt "This is the way to do it because we have always done it this way" from “This is the underlying reason for doing it" I like to take everything apart to see how it works. (This caused much distress to my parents when I was young. The family tube type TV all spread out in the living room was the low point. It going back together and working was the high point ) Mine was a genuine question without malice or subterfuge. Sometimes print does not convey intent well as there is no “tone” to it.

When you get to milking out the last ½ % or tenth of anything things get interesting and don’t always follow standard lines of thought or methods.
To me clutch engaged is in contact and being clamped by the pressure plate to the flywheel, not clutch pedal being pushed. Is this backwards from standard racespeak?

Geo

I think your general observation is correct.

In my case I am in the second group, although I have mastered the technique and used to do it daily. I stopped because it is unnecessary. But it's useful to at least know how to do successfully.

Geza

kurt M, I hope the tone of my response was not "off-putting". That certainly wasn't my intention. I truly wasn't sure I understood the process you described. My first thought was that "clutch engaged" meant exactly what you meant it to mean, but I didn't see a stop, however brief, into neutral in your description (for the rev match), which added to my confusion.