n4ji

iTrader: (1)

Mwhahaha... Power shifting on knotchy trannies! Is there any justice?

To me double clutching is a waste of time and energy for pressing your left foot down another time....

DoriftWolf

And when you do this you are doing absolutely nothing to help the engagement of the gears. Read the breakdown below and the explanation.

The primary purpose of rev matching is to keep the car balanced when selecting a lower gear, and is usually done combined with braking (heel-toe). This is so the additional engine braking of selecting the lower gear doesn't cause any additional weight transfer in the chassis. It is a smoothness technique, and any pro driver will tell you that smoothness is the key to speed.

Now for the technical part. WHY does this help?

You really need some understanding of how a manual transmission works, so here is a little bit of background.

A manual transmission typically has three shafts containing gears on it:
1) The Input Shaft: This is the shaft connected to the engine through the flywheel and clutch. When the clutch is engaged to the flywheel, this shaft spins at the speed of the engine. When the clutch is disengaged from the flywheel, this shaft spins freely based on the speed of the lay shaft.
2) The Lay Shaft: This connects the Input Shaft with the Output Shaft, with corresponding gears for each gear on the Output Shaft and a gear for the Input Shaft as well.
3) The Output Shaft: This is a splined shaft that is connected to the drive shaft. There are several gears corresponding to the number of speeds of the transmission. These gears run on bearings on this shaft, so they are moving independently of the shaft. Between these gears are collars connected to the shift linkage and are movable along the splines on the output shaft. On sides of these collars are “Dog Teeth” which correspond to holes on the sides of each gear. In a synchromesh transmission, between the gear and the collar, there are synchros. The synchros use friction help the collar and gear adjust their speed to engage the gears smoothly.

When none of the collars are engaged in a gear, then the transmission is in neutral, and the Input Shaft and Lay Shaft spin at engine speed, while the output shaft spins at road speed. When shifting gears you are moving the collar to engage one of the gears directly linking it to the output shaft, and then the power is transmitted from the engine to the road. They synchros and the clutch compensate for the change in speed between the Lay Shaft and Output Shaft by speeding up one and slowing down the other until they match speeds to smoothly engage. This is why when you downshift by putting in the clutch and selecting a lower gear, when you release the clutch the car slows down and the engine revs rise.

For a more in depth discussion on how a transmission works and diagrams check out:

How Stuff Works : Manual Transmission

Now the technique with what is actually happening.

1. Press in the clutch pedal disengaging the Input Shaft from the engine.
2. Move the gear selector into neutral. This disengages the collar from the gear the car is currently in on the Output Shaft.
3. Release the clutch, which will engage the Input Shaft back to the engine.
4. Rev the engine to the speed of the next gear by pressing and releasing the accelerator quickly. Take into account the revs will fall during the next step, but for the lower gear, this varies depending on the gearing of the car so this is something to figure out with trial and error. What this does is speed up the Input Shaft and Lay Shaft to the engine speed for the lower gear, which should match the current speed of the Output Shaft.
5. Engage the clutch disengaging the Input Shaft from the engine again. The revs will fall but if you compensate for the slight fall there shouldn’t be any issues.
6. Move the gear selector into the next gear. If done correctly, the Collar should be spinning at the exact speed it needs for the Dog Teeth of the next gear directly without relying on the synchros. This should be a very quick and smooth shift since the synchros won’t be engaging.
7. Release the clutch, engaging the Input Shaft back to the Engine. If done correctly the synchros should not engage and you should notice no change in engine speed or feel any significant weight transfer from engine braking.

From this explanation you should see why conventional single clutching does not work to rev match, since the Input Shaft and the Lay Shaft are disconnected from the engine and are spinning at their own speed independent of the engine speed or the road speed. Trying to rev the engine with the clutch in will only cause the flywheel to slip against the clutch when re-engaging and causing further frictional losses as well as advanced clutch wear.

BTW... for smoothness, I always rev match or heel-toe when selecting a lower gear. With enough practice you can do it fast enough and it becomes second nature.

With most piston engines, a single blip in neutral is sufficient, but with the rotary, I find that a double blip is necessary (or a longer single blip) because the revs fall much faster than with a piston engine.

I know this is a long explanation, but one of the keys to mastering a technique is to understand why you are doing it.

As with anything concerning performance driving, it is a "feel" thing and requires practice, practice, practice until it becomes second nature.

The source of this is a document I wrote for our customers because I was getting tired of trying to explain this individually, so any glaring errors are my fault alone. If you are interested, I'll post the rest of the document, which goes a little further into the performance aspects of this technique and why and how, and cover's heel-toe as well.

oakback

So you guys actually use your heel and your toe to heel-toe? I mean, I just use half my foot on one pedal (big toe and pad), and half my foot on the other pedal (maybe 3 toes/pads). Maybe I just have big feet?

DoriftWolf

I have wide and long feet, so for most cars, I can just use the corner of my foot on the brake and use the side of my foot on the accelerator. Pedal size and spacing has a lot to do with this, as does the shoes you are wearing.

I typically will move the pedals a little closer to each other when installing pedal covers to make this easier to do (my 180SX has Sparco pedals and I moved them about 5mm closer to each other which makes it a perfect distance for narrow shoes or bare feet (Major ouch in the summer... these b****s get hot!!!)

I still have the stock rubber pedal covers on the FC... and they are spaced just slightly wider than I would like to get a good grip on the brake and still hit the accelerator. I'm a big tall guy, so using the more traditional method is awkward for me in my comfortable driving position, but I try to practice it occasionally.

oakback

Yeah, I guess that's what my problem is. 6'3", knees already pressed for space.

RomeoFC3S

hi DoriftWolf,
i know some about transmissions but not very much

i came up with some dumb idea (normal driving, no intension of performance shifting), and i was wondering after i read ur explinations that i just had to ask you about my experience or should i say experiment.

i went to my fc and went off with the first gear (normal shift), then i tried shifting to 2nd-3rd-4th and 5th
without using the clutch! seems fine, little grind when i'm out off timing sometimes but other than that its almost like normal shifting!

HOW I DID IT?
clutch in = 1st Gear = little gas and clutch out.
(normal shift) then

*foot off the gas = wait 2sec or FEEL the road speed and engine speed when they're at thier ZERO resistance or same speed then shift in to 3rd!... and so on!

zero resistance:
engine is not pushing the tranny and tranny is not pulling the engine

is something worn out in my tranny?
is this crazy shifting bad? will something wear?


i'm so sorry this long *** msg ^_^
i jst thought i'd share some crazy experience of mine

1SxyRXy

if you use synthetic on your old tranny seals then it will leak through them and eventually ruining them

Mr. Gadget

All I have to say here

On Double Clutching - Sorry NZ, however its helpful when you 5th is gone - no grinding!!! Use for daily driving

On Rev MAtching - Performance Driving - takes a bit of practice - shaves seconds in autoX when you master.

On Heel Toe - Performance Driving

SureShot

My first car was an old 1949 Morris Minor (grandaddy of the Mini) all spurr gears, so all downshifts were double pedal & double clutch, and all upshifts were rev matched.

The next 3 cars were Austin Healey Sprites with no syncro in 1st.
Most early 60's sports cars had no 1st gear syncro.
I did well in autocross by getting into 1st in the corners since few drivers could.