What's the Best Combination of Gears?

[cRiPpLe_rOoStEr]

Well, nowadays even some big rigs are getting trannies with less gears, is not so uncommon to find some with only 9 gears...

[freebeard]

Occasionally6 -- My point was more that two extra shifts would cost 1 second at the traps. Not a point I should expect to resonate on a forum about eco-modding.
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VW transaxles have a larger gap between 2nd and 3rd. When I got a 5-speed conversion, it lowered third and had a 'low 4th' and a 'high 4th'. Fifth wasn't much use below 65-80, but it was a joy around town because you spent more time with two gears to choose from against 35-45mph speed limits.

[serialk11r]

aardvarcus you're spoiled with a C60. I have C56. 3000rpm in 5th is only 55mph.

More gears is better yes, and I would love to see 7 speed manuals everywhere. However being more realistic, a 6 speed like the C60 is a pretty good compromise for a small 4 cylinder engine. The 6th gear is a proper cruising gear that lets you follow traffic without going too much over 3000rpm (where a lot of engines start to really decline a lot in efficiency at low load due to friction), and the first gear is nice and short for starting and such. You can tip the scales more in the economy direction by making the 6th taller (a 2ZZ powered small car can hit 160mph in 6th with some drag reduction) and spreading 1-5 a little more.

I would be extremely happy with a slightly destroked engine and a C60, it would leave some gas mileage on the table but it would be pleasant to drive and still do okay on the highway. Yea if you wanted maximum gas mileage you could spec a gearbox that lets you do 55mph with 1500rpm (assuming you have a motor that can pull this off, I doubt my 1ZZ can), 5th put you at like 1500rpm for 45mph, and have 4th place you right at like 1200rpm for 25mph, but the giant gear spacing would drive me nuts when shifting and having to downshift to 3rd to accelerate hard would be really weird.

[aardvarcus]

Originally Posted by serialk11r

aardvarcus you're spoiled with a C60. I have C56. 3000rpm in 5th is only 55mph.

More gears is better yes, and I would love to see 7 speed manuals everywhere. However being more realistic, a 6 speed like the C60 is a pretty good compromise for a small 4 cylinder engine. The 6th gear is a proper cruising gear that lets you follow traffic without going too much over 3000rpm (where a lot of engines start to really decline a lot in efficiency at low load due to friction), and the first gear is nice and short for starting and such. You can tip the scales more in the economy direction by making the 6th taller (a 2ZZ powered small car can hit 160mph in 6th with some drag reduction) and spreading 1-5 a little more.

I would be extremely happy with a slightly destroked engine and a C60, it would leave some gas mileage on the table but it would be pleasant to drive and still do okay on the highway. Yea if you wanted maximum gas mileage you could spec a gearbox that lets you do 55mph with 1500rpm (assuming you have a motor that can pull this off, I doubt my 1ZZ can), 5th put you at like 1500rpm for 45mph, and have 4th place you right at like 1200rpm for 25mph, but the giant gear spacing would drive me nuts when shifting and having to downshift to 3rd to accelerate hard would be really weird.

Yeah, my RPMs aren’t quite that high, but still pretty high especially on the interstate. Just as an FYI if you ever have to have your C56 worked on there is a factory Toyota 0.725:1 5th gear that is a direct replacement, definitely worth considering.

Oh, as far as the crazy downshifting goes, imagine pulling the car out of sixth and putting it into second. The peak power band on a 2ZZ engine is 6200-7800 RPM, which is 49-61 MPH in second, so if I need to pass someone doing 45 or less in the 55 and I only have a small window to pass it comes out of 6th and into 2nd.

The options for final drives in C60s are 3.941:1, 4.312:1, and 4.529:1 all US spec Celicas got the 4.529 from the factory. I would love to drop in the 3.941 gear set, my only concern is making it hard to take off in first. I have not yet found anyone making a lower first or a taller sixth for the C60.

[Frank Lee]

Originally Posted by Occasionally6

In the context of:
If there is a choice between only having gears 1 and 3 (say) and gears 1,2 and 3, where ratios 1 and 3 are the same, and 2 splits them, three gears will allow the engine to be operated closer to its highest efficiency than will two of them.

Yeah- especially if you're driving a tractor.

In the context of the real-world trip- for example when I go out of town- I'm accelerating through the lower gears for mere seconds then droning on for hours in top gear. With, say, 3 gears and a 0-55mph operating envelope, the engine might fall outside of it's "perfect" rpm range for what- .001% of the trip? A minimally geared transmission that suffers less internal friction losses would be a fe benefit to me the other 99.999% of the time. Heck, maybe two gears would be enough... or a smaller engine (thinking of the 2.3 torque monster in the Tempo).

More gears maybe would have some benefit in trip scenarios heavy with urban, heavily loaded vehicle, or mountainous conditions... but I don't have those.

The act of shifting is itself quite inefficient: the flow of power and thus acceleration is interrupted, the throttle snaps shut and all the engine's whirly bits have to decel then "recel", similarly the flows in the engine's tracty bits have to slow then restart. Best to avoid that as much as possible, I think.

[serialk11r]

Originally Posted by aardvarcus

Yeah, my RPMs aren’t quite that high, but still pretty high especially on the interstate. Just as an FYI if you ever have to have your C56 worked on there is a factory Toyota 0.725:1 5th gear that is a direct replacement, definitely worth considering.

Oh, as far as the crazy downshifting goes, imagine pulling the car out of sixth and putting it into second. The peak power band on a 2ZZ engine is 6200-7800 RPM, which is 49-61 MPH in second, so if I need to pass someone doing 45 or less in the 55 and I only have a small window to pass it comes out of 6th and into 2nd.

The options for final drives in C60s are 3.941:1, 4.312:1, and 4.529:1 all US spec Celicas got the 4.529 from the factory. I would love to drop in the 3.941 gear set, my only concern is making it hard to take off in first. I have not yet found anyone making a lower first or a taller sixth for the C60.

Yea I know about it but they don't make the special gear puller anymore so it's really annoying and I'd have to pay someone to do it, and I would never be able to recoup the cost in gas savings. I'm just going to buy a C60 when this drivetrain gives out. The synchros are pretty much totally shot so it's only a matter of time.

I actually like the 4.529 with 0.725 6th gear setup, maybe my 1ZZ isn't so healthy (it is a 2000 model year afterall) but pulling from a stop it feels like it struggles a little, I think the slightly shorter 1st would be nice, and I would be pretty content to be able to cruise at 3000rpm without feeling like I'm going to be the victim of road rage.

[cRiPpLe_rOoStEr]

Originally Posted by Frank Lee

The act of shifting is itself quite inefficient: the flow of power and thus acceleration is interrupted, the throttle snaps shut and all the engine's whirly bits have to decel then "recel", similarly the flows in the engine's tracty bits have to slow then restart. Best to avoid that as much as possible, I think.

No wonder the AMTs, including DCTs, are usually based in a non-synchronized gearbox, thus allowing them to be shifted without the use of the clutch.