I read the recent thread here about whether engines last longer with auto or stick transmissions and it got me thinking. There was some mention of how different shifting points cause more, or less wear on the engine, etc. I've been driving manuals for over 20 years, but never really ever asked any experts about the best way to shift, or the effects of different techniques.
My impression was that if you wanted to accelerate in the fastest way possible that you shifted at the peak of the horsepower curve of your engine's output. If you wanted the most power available, like if you were towing something, then you wanted to keep your rpms close to the engine's peak torque rpm. If you wanted better MPG, you kept your rpms as low as possible. And after all of this, don't let the rpms fall so low that you "lug" the engine bacause that would cause excessive wear. After a while, I just seemed to gravitate to shifting at a point where I felt it would be an easy, smooth transition into the next gear, so that a passenger would not feel a noticeable increase or decrease in the rate of acceleration or deceleration.
So my question is what is your recommended shifting technique to optimize these various situations:
1. Maximium acceleration
2. Best MPG
3. Minimize engine wear
4. Minimize clutch/tranmission wear
5. Smoothest ride
Also, how exactly do you determine when you should downshift so as not to lug the engine?
Manual Transmissions -- Different Shifting Techniques?
- Thread starter Cogito
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for 2,3,4, 5 accelerate slowly beyond the "lugging point" simple as that. Max acceleration shift at "maximum hourspower" which is beyond the max torque curve.
For max acceleration, you usually should shift past Max HP. Here is why...
Look at your torque curve and multiply the value at X RPM by your transmission's first gear ration. Figure out what RPM that would be in second gear and multiply that gear ratio by the torque at the new RPM.
Don't shift until you hit redline or until the next gear makes more torque when multipled like above. (Which ever happens first)
My camaro for example. http://i22.photobucket.com/albums/b345/cmoliver/ronnie/DSC00165.jpg
1st gear = 2.66 6500 RPM = 300 ft lbs. Multiplied by 2.66 = 798 effective ft lbs
2nd gear = 1.66 1st at 6500 = 2nd at 4060 RPM Torque at 4050 = 350 ft lbs Multipled by 1.66 = 581 Effective ft lbs.
If you look at the link (it a dyno graph). You'll see my HP peaks around 6500 but I should actuall shift at a higher RPM because the numbers above show more torque is still being sent to the rear wheels in 1st vs 2nd at 6500 rpm. I don't want to go past 6500 because I don't want to buy a new engine anytine soon. But if all I wanted to do is accelerate, then I would definately want to shift at a higher RPM.
Here are the rest of the gear ratios for a Camaro if you want to check for yourself. Every car is going to be different due to different torque curves and different gears. Hope this helps.
3rd gear = 1.33
4th gear = 1.0
5th gear = .74
6th gear = .5
Kestas
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To minimize wear of the syncronizers I avoid "slamming" it into gear with the shifter. Instead, I put just the right amount of pressure on the shifter so it "falls" into gear. This pressure is developed by feel after getting used to the car and how it drives. I also shift into first just before coming to a stop while the car is rolling slowly. That way the synchronizer teeth don't get pinched as they sometimes do when you're trying to put it in gear when the car is stopped.
To minimize clutch wear, let the clutch slip no more than it absolutely has to, to get the car moving and maintain smoothness. Once the car is moving, you need to let the clutch slip less for the higher shifts. For some of the higher shifts you don't have to let the clutch slip at all.
It isn't peak horsepower that counts, it's the torque. At least in apps where the horsepower and torque do not rise in lockstep throughout the rev-range. In the Accent, from a seat of the pants standpoint (and I'd bet also on the dyno), the torque maxes at 4000. The manufacturer quotes max horsepower at 105 ponies at 5800 rpm. I can tell you, however, that the thing is all done, PULL-wise, at 4500 at the most. The run on up to a (pointless) red-line of 6800 rpm is loud and dramatic, but again, pointless. The greatest acceleration in this car is in a narrow band between 2000-4200RPM. In motorcycles, is not the "power band" defined as the period of peak torque, rather than horsepower? Certainly in my application, the peak torque is falling off right as the engine is building to peak horsepower. I remember the same result from dyno-testing the bike magazines used to run on the new superbikes from years ago.
I doubt anything has changed.
Hmmm, good questions. I have driven nothing but sticks since I got my license 23 years ago. 1) About 4,000 rpm, I don't like revving any higher. 2 through 5) About 2,500 to 3,000 rpm. I downshift whwnver I feel the engine is running too low rpms. I've been doing it so long I go by sound rather than the tach.
For max acceleration, upshift to the next gear at the HP peak. If the gear ratios are properly selected, the RPM should drop to the torque peak. Running from torque peak to HP peak should deliver maximum acceleration.
Cheers
JJ
GM doesn't know how to set gear ratios, that is why there are a few exceptions. The gears are too spread out (more than likely for fuel economy), and holding a gear past peak horsepower puts you where you should be. My RSX Type-S drops you to peak torque or higher on every single upshift at peak horsepower. The M3 is the same way, and every Porsche I've ever been in.
I get my best fuel economy in the city by flooring it and shifting at 2500 rpms. This moves me at the same rate as traffic and gives me about 24-25 MPG, which is above the EPA rating of 21. Even with the engine floored (lugging), I move the same speed as everyone else.
Shift too far below your power peak and you risk shifting into a higher gear at too-few RPM, so you'll be REALLY out of the power curve.
I don't think you can rule HP out of the equation. HP is the ability to do work, in this case to move your car faster. Torque is a measure of force that doesn't require motion.
I think races are won with HP. HP always wins at the track.
[ March 13, 2006, 03:51 AM: Message edited by: robbobster ]
For maximum fuel economy, I follow John and Helen Taylor's technique. They are the current world record holders for fuel economy.
Shift up around 2000RPM. If you need more oomph, just before 2500RPM will be good.
If you have to slow down, brake gently and shift down when the RPM falls below 1500.
Many people commented on how fast I shift up even on a suburban street and hit 5th gear moving around 60kph. It is hardwork but it pays off. I get 2-3km/L more than most other people with any car I drive.
See Taylor's new efforts in circumnavigating the globe in less than 50 fillups.
http://www.fuelchallenge.com/
98LS Won is correct. No doubt.
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.
Shifting the diesel in the truck is a bit different than in say a Honda Civic. I'm most concerned about powertrain life, especially the clutch, so one needs to avoid slipping the clutch as mcuh as possible. In general I like to shift so that it's an effortless couple of finger shift into the next gear, which seems to require 'catching' the next gear at around 1500 rpm. This means that I can shift at lower rpm when going downhill and I may need lots of rpm when going uphill. Trying to shift too quickly with lots of rpm is often a clumsy affair, but a bit of pedal works better than babying it. In 1st gear I notice that one can carefuly let the clutch out while idling and then give it some fuel, I guess due to the torque, and this seems to be the best way to minimize clutch wear.
The quickest shifting gearbox that I've used was on the RD400, which seemed to shift with ESP :^)
1. Maximium acceleration
Best acceleration is achieved by running the engine such that the area under the HP curve is maximized. This invariably requires you to shift beyond paek HP and most of the time it requires one to shift at the RedLine.
2. Best MPG
Best MPG is generally achieved by running the engine at as low an RPM as you can (often with the caveat of not lugging the engine).
3. Minimize engine wear
See above, but add an additional caveat that running just above idle may have slight more wear than running another 200 RPMs higher due to low oil flow rates and often low oil pressure. So there are times when running 1 gear (ratio-wise) higher than where the engine will tollerate operation may reduce wear. Widely spaced gears in a transmissions do not enable this property.
4. Minimize clutch/tranmission wear
Clutch: Use as little power as possible when the clutch is in the friction zone. And traverse the frictioin zone with only moderate speed.
Transmission: Run at the lowest power levels that achieve the desired vehicular speeds.
5. Smoothest ride
Double declutch the transmission, and feather the clutch through the friction zone, while operating at the lowest power levels sufficient to achieve the desired speed and acceleration goals.
The biggest fluctuation in torque in my motor from 3000-7200 rpms is about 10 ft/lbs. It's mostly flat and proves that VTEC does magical things. After 7200, torque takes a dump. It is all about gearing. Gearing will help you decide where to shift. The best place to shift will vary in every gear.
Cogito, I think he's using "declutch" similarly to someone saying "deskin your shins". Letting the clutch pedal out allows the Layshaft to turn at the speed that brings the transmission gear to speed where the synchronizers work better, so the subsequent shift can be smoother/quicker.
"Mitch Alsup's post answers each of your questions properly."
Maybe, maybe not. I hear a fair number of people talking about shifting at low rpms, when in fact the shift needs to take place at an rpm range where one could dispense with using the clutch if needed. This means that it's not as important as whant rpm the shift is engaged at, as that will differ depending upon speed, load and grade, rather the rpm that the shift takes place is more important. A small but important distinction.
Double-declutch: probably = double-clutch.
Feather the clutch: slowly and lightly engaging the clutch with little throttle, like when starting in first without using the throttle.
Mitch's post sounds about right, with 1sttruck's addition in brackets.
1sttruck: Is your Cummins programmed to maintain 600rpm on idle? You can start in any gear (if you wanted to) without pushing the accelerater on those ones. 2nd gear starts without touching the pedal work good on them.
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