I hear that a 10 speed (aka 10 gears) AT gives better fuel economy. Why can't they get the same fuel economy on a 4 speed AT like in my 02 Mustang GT? If it were possible I'd consider replacing my 4-speed AT with a 10 speed AT if there's a significant improvement. I would imagine that the AT electronics would need to be upgraded also. I wouldn't want to mess with a 10 speed manual transmission though. I have a 4-speed AT in my Xterra also.
The more gears, the better the transmission can keep the engine in the most efficient part of the power band.
I don't know that there are any aftermarket (or junkyard) 10-speeds that will fit your application, though maybe others are better able to comment on this. Even if there were, I am pretty sure that the cost would far outweigh the benefit in mileage. I think you'd be better served with the normal things to optimize economy (engine maintenance, good tires, right tire pressure, etc).
I am not aware of any 10-speed manuals for passenger cars, though some heavy trucks have them.
However a 10 speed automatic transmission is much more expensive to begin with and you can probably forget rebuilding it when it goes bad.
I prefer fewer speeds, 3 or 4 is ideal (all I've ever owned) but I wouldn't sneeze at a Powerglide (2-speed). Although there have been one-speed automatics like the Buick Dynaflow that's giving up a bit too much flexibility.
You won't get a modern 10-speed automatic into your Mustang. Odds are, it won't even bolt up to the flywheel/ crank assembly. Trying to do so would require you to fabricate custom parts, which is extremely expensive. Next, comes the problem of size. A 10-speed is much bulkier than a 4-speed, so the transmission tunnel under your shifter won't accommodate it. They're also longer, necessitating a shorter driveshaft, which is also expensive to fabricate. Tack on the added inconvenience of the output shaft flange likely not matching that of your existing transmission, and you're in for a real headache with just the driveshaft problem. That all needs to stay balanced. Even if you Frankenstein all of that to work, the most problematic part of all is engine /transmission interfacing. Modern engines and transmissions are controlled by the PCM via programming. The computer knows the shift points of your 4-speed and engine based on set parameters such as throttle position, RPMs, etc. They're not the fossilized hydraulic devices of the 1970s and before, which were self contained and would change gears on their own with no computer input, and worked with any engine it could bolt to. Your computer won't known when to change the gears on the 10-speed, and programming it would require a pro. You would need a complete overhauling of the PCM and wiring for the transmission.
Replacing a transmission in a late 90s/ early 2000s Ford Ranger for example, someone would need to watch what transmission they have. The 4R44E and 5R55E appear to be exactly the same transmission from the outside, but inside, some minor changes were made to make a 5-speed out of a 4-speed. A 4-speed PCM can't work with that tranny because of this problem, likewise with a 5-speed. Wiring and programming conflicts. It's extremely complex stuff these days.
More speeds, more efficient....did you ever own a mountain bike? Same situation....more speeds means easier to pedal up to speed.
It may be possible?? to transplant a 10 speed into your SN-95 chassis. (If you have a lot of $$$$)
The following youtube channel accomplished the swap into a Fox body chassis. Your SN-95 is basically a modified Fox body with additional bracing from the factory.
https://www.youtube.com/watch?v=R90eCFf-XSI
It makes me wish that I were rich.
A 10 speed transmission will get you better fuel economy when compared to a 4 speed.
I would not recommend doing a swap from 4 speed to a 10 speed transmission because of the size and making sure that it fits properly.
