Manual Transmissions -- Different Shifting Techniques?

[ZeroDynamic]

"It would be a rare vehicle that will accelerate best when shifting at your HP peak. I can't concieve of this situation, though.
You almost always have to rev it up much higher, before shifting, to get the most torque at the wheels."

Actually, my Inline 6 bimmer makes 252 tq @3250 rpm.
My engine also make 247 hp at 6000 rpm.

So shifing at 6000 rpm works very well for me.. I get the pull and the push and when I shift, i get more pull again! Way better than a V style engine.

 

[TallPaul]

Well my '95 F150 4.9 L inline six makes peak 265 pound feet at 2000 rpm and peak 145 hp at 3400 rpm. When I want to move fast (and of course that is not very fast being more of a tractor engine) I usually shift around the mid 3000's which puts me in the mid 2000's in the next gear. May not be fast, but that big block torque feels great.

 

[cousincletus]

I guess it depends a lot on the car. I shift the Cavalier (2200 OHV w/o much horsepower, I think about 120) at just under 3,000 rpm in every gear. Sometimes on the merge lanes I have to get it up to 65-70 mph in 4th before I shift into 5th. I'll go a little over 3K then. But don't shift a car transmission like your Peterbilt. Big truck transmissions have no synchronizers. Therefore, yoy have to double clutch (or not use the clutch at all and match your input/output rpms.

 

[Mitch Alsup]

Double deClutch is a series of actions between operating in one gear and operating in the next lower gear. Double deClutch is a British phrase which is often hearrd as Double Clutch, Double shift,... By whatever means, it is the following sequence:

A) back down throttle so that no power is going to the drive wheels and no power is comming out (say 7% throttle)
B) clutch pedal goes down
C) shifter goes to neutral
D) clutch pedal comes back up
E) gas pedal is pushed in one short stabbing motion. This moves the engine and the transmission mainshaft to the RPMs desired after the next set of actions. The transmission layshaft is still connected to the rear wheels via differential. The whole purpose here is to get the mainshaft and the layshaft turing at the same speed wrt the to-be-selected gears. The engine will leap above the desired RPM band and then descend as the next 3 action transpire.
F) clutch pedal goes in
G) shift into desired gear--just as the mainshaft passes through the desired RPM so the dog teath can enguage without excess force.
H) clutch pedal comes back out. Be careful to enguage clutch slowly through the friction zone.

If you can orchestrate these actions quickly and smoothly, you will have taken all of the load off the synchronizers and can make them last forever. The old "crash" boxes without shynchronizers HAD to be shifted like this to last.

 

[mechtech]

zerodynamic - You shift at 6,000 RPM. Fine and dandy! But that is different than maximizing your acceleration.
Mitch A - I don't think that lugging a modern engine after it is broken in will hurt anything.

 

[Cogito]

Mitch, if doing the "double-clutch" maneuver saves wear on synchros, what is its effect on the clutch plate? Doesn't engaging the clutch twice instead of once, per shift, cause extra wear on the clutch? Also, is this technique only for downshifting, and if so, why?

 

[Palut]

quote:

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Originally posted by Cogito:
Also, is this technique only for downshifting, and if so, why?

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I have to double clutch every time I shift from 4th to 5th gear. I've read that it's common for my car's tranny to grind into 5th. I do it like this:

Clutch in
shifter into neutral
clutch out
let engine speed drop to desired rpm
clutch in
shifter into 5th
clutch out like normal

Even though I only do this when going into 5th, I've done it so much that it's now an automatic process for me.

 

[Cogito]

Palut, when you say 'let engine drop to desired speed', what exactly does that mean?

 

[brianl703]

If you just keep the clutch pushed in long enough, it'll have the same effect as double-clutching on upshifts.

 

[Palut]

quote:

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Originally posted by Cogito:
Palut, when you say 'let engine drop to desired speed', what exactly does that mean?

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When I push the clutch in, the engine speed starts dropping towards idle. I just let the clutch out when rpms reach the speed that I want.

 

[rpn453]

quote:

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Originally posted by Cogito:
Mitch, if doing the "double-clutch" maneuver saves wear on synchros, what is its effect on the clutch plate? Doesn't engaging the clutch twice instead of once, per shift, cause extra wear on the clutch? Also, is this technique only for downshifting, and if so, why?

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The clutch only has to change the speed of the tranny internals, so it doesn't see much load during a double-clutch. The extra clutch wear would be minimal.

It definitely makes more sense for downshifting than upshifts. I double-clutch whenever I have to downshift 2 gears, and often even for a 1 gear drop. It feels so nice to shift when there's no resistance! As Brianl703 mentioned, the tranny is already slowing towards the proper rpm during an upshift, so double-clutching is of minimal to no benefit there. But on a downshift, the dropping rpms take the tranny even further from the ideal rpm for shifts.

For anyone confused on this topic:
With the clutch disengaged and the tranny out of gear, there are three things spinning at different rpms that should ideally be matched for minimal wear. Basically, these are: engine, input shaft of tranny, and tranny output shaft (with driveshafts and wheels connected to the output shaft). Double clutching and/or synchros match the latter two, and then you can rev-match the engine to reduce clutch wear and drive smoothly.

[ March 16, 2006, 06:19 PM: Message edited by: rpn453 ]

 

[Cogito]

quote:

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Originally posted by Palut:

quote:

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Originally posted by Cogito:
Palut, when you say 'let engine drop to desired speed', what exactly does that mean?

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When I push the clutch in, the engine speed starts dropping towards idle. I just let the clutch out when rpms reach the speed that I want.

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I know, you said that in your previous post. How do you know what rpm you want? How do you determine that?

 

[brianl703]

Pay close attention to the relationship between the tachometer and the speedometer, you'll soon learn what RPM you want for what gear.

By the way, the tachometer and speedometer in my car have been designed so that in 4th gear (1:1 ratio) the needles point in the same direction. That is, if the speedometer needle is pointing straight up, so will the tachometer needle. If the speedometer needle is pegged (won't ever happen) the tachometer needle will be too (and the engine will be in pieces all over the road...)

 

[Palut]

quote:

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Originally posted by Cogito:
I know, you said that in your previous post. How do you know what rpm you want? How do you determine that?

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From experience. My car turns about about 1000 rpm/25 mph in 5th gear. About 2300 rpm at 60, which is when I usually shift into 5th. If I'm at a higher speed, I do a little quick math in my head to figure out what rpm I should shoot for.

In my particular case, I pretty much have to use the clutch to double clutch up into 5th. My poor tranny is so sensitive that just a couple hundred rpm will make the difference between grinding and shifting smoothly. I'm grateful that 5th is the only gear that does this!

Although double clutching upshifts does seem to make a difference on cold mornings...

 

[ex_MGB]

quote:

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1. Maximium acceleration
2. Best MPG
3. Minimize engine wear
4. Minimize clutch/tranmission wear
5. Smoothest ride

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I agree with Mitch but will add a few thoughts based purely on my 6 speed MT 2001SE Miata:

1. First you shift above redline, second at redline, 3rd, 4th, 5th below redline. By shifting above redline out of first you drop into second's powerband just right. If you shifted t redline you're too low in second's powerband.

2. MPG is achieved by keeping rpm's down though if you accelerate too slowly your mpg is less because your best mpg is while in top gear.

3. Wear means many things, not just wear metals. The Miata, in order to maintain peak performance needs to be thrashed from time to time.
It's designed to last a very long time while driven in a spitited manner.

4. Shift smoothly. Downshifts keep the clutch friction surfaces "in tone". Baby it too much and the clutch will accumulate uneven deposits.

5. Smooth ride. The Miata is not smooth around town, double clutching first to second helps. Rev matching helps. It's smoothest at WOT banging on redline, do it right and you can barely feel the shifts.

 

[Cogito]

Thanks, Palut, I see what you meant now.

My engine will pull smoothly in 4th gear from around 2,000 rpm without lugging. Does this hurt anything mechanical; would it be better to downshift at that point or not? Also, does anyone know what exactly is happening in the engine, or what are the negative effects caused by lugging?

 

[Titan]

Cogito, I'd recommend going to a website called: www.howstuffworks.com
Look in the auto section about manual transmissions. It takes a lot of the mystery and voodoo out of it. When you understand how the crankshaft and flywheel rpms relate to the clutchplate, how the clutchface and transmission main drive relate, then how the transmission main drive relate to the driveshaft, and how the synchronizers match the dog-teeth speed to the layshaft, and how the layshaft and driveshaft rpms relate, it will be perfectly understandable what these people are nattering on about! I may not have used the same terminology as on that site, but, it doesn't really matter, it's the concepts and how they all fit together that matters. All you'd really need to know then is how your engine rpms correlate to it's particular torque and HP curves, and you'll be an expert!

 

[Titan]

Originally posted by ex_MGB:
[QB]

2. MPG is achieved by keeping rpm's down though if you accelerate too slowly your mpg is less because your best mpg is while in top gear.


I disagree with this statement. Well, if you REALLY mean it, I agree with it, but, you'd have to define "too slowly". If, by "too slowly" you mean it takes several minutes to reach 30 mph, then, yes, we agree. However, if you mean push the skinny pedal hard and hurry up to get to cruising speed, then I disagree.

The laws of physics determines what is most efficient, and RATE OF ACCELERATION is a key factor in use of energy to move an object. Increase the RATE, and you increase the power required. Your muscles are engines...try to move a heavy object quickly from one point to another instead of moving it smoothly at a lower speed. It will be obvious to you which method takes more energy to accomplish.

In cars, gentle throttle use combined with timely shifting yields the best economy.

Realize that you may get better economy to skip gears altogether. When trying to get the best economy, I often shift 1st-3rd-5th. 1st to get moving off the line quickly enough not to cause traffic snarls, third is just to gain a bit more speed...gently...until I get going fast enough to be in 5th without lugging the engine. I can get in the mid-thirty mpg range IN TOWN in a manual transmission car rated at 22-29 Hwy. It takes foresight in shifting, braking, and a light touch on the throttle, combined with appropriate coasting in neutral downhill. Best this car has ever gotten at speed on the HWY is 34...but, I don't use the neutral coasting trick on the Hwy, plus the air resistance is signficant on the Hwy as opposed to city speeds....so my city driving inefficiencies equal the loss of economy provided by air resistance on the Hwy. Oh, I must say my "city" traffic isn't like most city traffic. Very light, small-town traffic, not sitting at redlights for a couple of changes, etc.

HOWEVER, I don't often drive this way, as I don't think it is too good for the engine. I usually drive at higher rpms, rarely using 5th unless going above 50 mph. Risking lugging is good for fuel economy, but, it's not good on the engine.

 

[Cogito]

quote:

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Originally posted by Titan:
Cogito, I'd recommend going to a website called: www.howstuffworks.com
Look in the auto section about manual transmissions.

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Thanks, Titan. That's an excellent site. I am now illuminated.