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aardvarcus · 10-29-2013, 11:21 AM

So would my original idea work like what you're saying, where you would have short closely spaced gears in 1-4 with a tall FDR, then you would still have peppiness with higher efficiency? Would having the last gear (say 6th) be way out there help or hinder, since that would make the range wider? Or would it just make more sense to have an extra gear in between 5th and 6th?

Regarding the TC, would that be when it is locked or unlocked? I would imagine if it is while locked, and having taller gears like you say, that would be more efficient or equal to a manual?

Yes, as long as the first few gears are low enough a tall final drive would make the most of peppiness and efficiency. The spacing is more a function of how big your engines sweet spot of BSFC is, if you have a big wide area you don't need them spaced as close, versus if you have a narrower peak you would want them closer. For example, looking at your 1ZZ FE chart, your BSFC is pretty darn good from 2500 to 4000 rpm. Ideally the spacing on your transmission should be such that if you shifted in any of your first few gears at 4000 you would land at 2500 or more, so to still be in your BSFC sweet spot. Different engines will have different requirements.

For mainly open highway driving done with the cruise control set (not P&G), having 6th gear way far out is fine. It is not that bad to be out of your ideal range for a few seconds revving up the engine a little higher in the previous gear before you shift to your overdrive gear. For example, on my car for highways I typically accelerate first through fourth and will get going the speed I want in fourth and then shift it into sixth and set my cruise. No fifth involved unless I am getting on the interstate. When I need to make a pass or accelerate back up to speed, I pull the car out of sixth down into a lower gear 2nd-4th, complete my pass or acceleration, and then put it back into sixth. My car barely ever sees 5th gear, it just isn’t in a usable range for acceleration and my gears are so low that 5th isn’t good for cruising unless I am doing 40mph or less.

That is with the torque converter unlocked, when it is locked up it is basically like a direct drive just like a manual, but in most cases even with the torque converter locked up there is more internal friction in an automatic. That being said, with present gearing choices you can see in the EPA estimated numbers the punishment for the extra friction of the automatic is less than the punishment on the manuals of the super low gears when driven normally. The real advantage of the manual is the controllability, the ability to react and plan ahead when and how to accelerate and the ability to put it in neutral and just coast along. Pair that with “correct” gearing and you have a recipe for success.

10-29-2013, 11:21 AM	#10 (permalink)
aardvarcus Master EcoModder Join Date: Apr 2012 Location: Evensville, TN Posts: 676 Deep Blue - '94 GMC Suburban K2500 SLE 90 day: 23.75 mpg (US) Griffin (T4R) - '99 Toyota 4Runner SR5 90 day: 25.43 mpg (US) Thanks: 237 Thanked 580 Times in 322 Posts	So would my original idea work like what you're saying, where you would have short closely spaced gears in 1-4 with a tall FDR, then you would still have peppiness with higher efficiency? Would having the last gear (say 6th) be way out there help or hinder, since that would make the range wider? Or would it just make more sense to have an extra gear in between 5th and 6th? Regarding the TC, would that be when it is locked or unlocked? I would imagine if it is while locked, and having taller gears like you say, that would be more efficient or equal to a manual? Yes, as long as the first few gears are low enough a tall final drive would make the most of peppiness and efficiency. The spacing is more a function of how big your engines sweet spot of BSFC is, if you have a big wide area you don't need them spaced as close, versus if you have a narrower peak you would want them closer. For example, looking at your 1ZZ FE chart, your BSFC is pretty darn good from 2500 to 4000 rpm. Ideally the spacing on your transmission should be such that if you shifted in any of your first few gears at 4000 you would land at 2500 or more, so to still be in your BSFC sweet spot. Different engines will have different requirements. For mainly open highway driving done with the cruise control set (not P&G), having 6th gear way far out is fine. It is not that bad to be out of your ideal range for a few seconds revving up the engine a little higher in the previous gear before you shift to your overdrive gear. For example, on my car for highways I typically accelerate first through fourth and will get going the speed I want in fourth and then shift it into sixth and set my cruise. No fifth involved unless I am getting on the interstate. When I need to make a pass or accelerate back up to speed, I pull the car out of sixth down into a lower gear 2nd-4th, complete my pass or acceleration, and then put it back into sixth. My car barely ever sees 5th gear, it just isn’t in a usable range for acceleration and my gears are so low that 5th isn’t good for cruising unless I am doing 40mph or less. That is with the torque converter unlocked, when it is locked up it is basically like a direct drive just like a manual, but in most cases even with the torque converter locked up there is more internal friction in an automatic. That being said, with present gearing choices you can see in the EPA estimated numbers the punishment for the extra friction of the automatic is less than the punishment on the manuals of the super low gears when driven normally. The real advantage of the manual is the controllability, the ability to react and plan ahead when and how to accelerate and the ability to put it in neutral and just coast along. Pair that with “correct” gearing and you have a recipe for success.