Quote:
Originally Posted by Thenorm
well in theory, if you were to have the BSFC map for your engine you would be able to see how wide, in rpm, the "island" is where you acheive your lowest BSFC. on my Ford Focus zetec it is from 1500 to 3000rpm.
So the minimum ideal closeness is gear spacing would be where when you upshift at 3000 you dont drop below 1500 for the next gear. Of course the closer your ratios, you can stay closer the centre of that sweet spot.
as a rule of thumb i think more gears are better. That why there are 7, 8, and 9 gear transmisison coming out, so you can always be in the BSFC sweet spot.
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I see what you're saying. The best gear set is whatever keeps it in the 'sweet spot' of the BSFC map. For this exercise, I was more trying to determine a generic rule of thumb for the best gears. But I am a visual and kinetic learner, so let's say we use the BSFC map of my Corolla.
I started a thread about that already.
Decoding & Breaking Down the 1ZZ-FE Engine BSFC
Also, I've heard there are issues with having more gears, especially with efficiency. I guess that can be offset by keeping the engine in the best range, right?
Quote:
Originally Posted by RobertISaar
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Thanks for that link. I'll play around with it some more. I already tried aardvarcus' gear ratio numbers and messed with it, but for consistency I will try my Corolla's numbers when I get a chance.
Quote:
Originally Posted by aardvarcus
The super low final drive makes takeoff quick and peppy, but it bites me when my crusing RPMs are high. I plan on regearing the final drive on my car to a 3.9 when the transaxle needs rebuilt, but I will lose the peppiness on takeoff to gain my better cruising rpms. If my car had 5th at .725 and 6th at 0.50 or if 1-4 were lower and I had a taller final drive would also be pretty ideal for my car, but in the world of just picking between drop in parts you have to make compromises . Different cars with different RPM ranges, power bands, weights, etcetera will require different transmission options. If I was starting with a blank sheet of paper and could have any transmission I wanted, I would get one with the widest range between first and last gears, and then adjust the final drive to suit the car and driving style.
The automatic transmissions have a torque converter, which basically acts like a lower gear on high torque loads, thus you can get away with a lot taller gears and still have some of the peppiness down low. The disadvantage is that automatics have more losses, so you are giving up HP to get that better gearing.
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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?
@Old Mechanic, I'm not sure what those numbers are or what you mean, can you explain further? Thanks!