Ok, so I understand how gears work and how a transmission works. I get what a gear ratio is between two gears only. How do they come up with the gear ratios for a transmission. Like 4.11 or 3.73? What exactly does this mean and how does it practically translate for me. For example, I have a 1988 744 Turbo with and AW71. I don't know the gear ratio. I want to put in a m46 or m47 and I was wondering how this would affect gas milage, acceleration, etc. If you could explain all this, it would be great.
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'Where's your common sense?' 'It left me when I was 5'

The examples you give are for the rear axle (final drive), not the transmission. They are always written as a ratio of revolutions of the input gear (or shaft) compared to the number of revolutions of the output gear (or shaft). For consistency, it is almost universal that ONE revolution of the output gear is used.

So... a rear axle with a 3.73:1 gearset will require 3.73 turns of the drivehaft for one full turn of the rear wheels (on the ground so they turn as one unit). You could also say that for every 100 wheel revolutions, the driveshaft will turn 373 times. Substitute a four-eleven rear, and the driveshaft will turn 411 revolutions for the same 100 revolutions of the wheels. More torque multiplication, more noise, more fuel, less efficiency.

AW71 equipped turbo 700s came with a rear axle ratio of 3.73. M46 turbo 700s came with a rear axle ratio of 3.54. If you convert your AW71 equipped car to M46, you will find that first gear is a little short.

Converting to M46 will give slightly better highway economy. The AW71 is very rugged and less likely to give trouble than the M46/OD. The only shortcoming of the AW71 is the tailshaft bushing and seal, which need to be replaced every 150,000 miles or so.

I prefer the M46/OD, but the AW71 in our 220,000+ mile 760T shifts perfectly.
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john

4.11 and 3.73 are usually final drive gear ratios, the gearset in the differential. the gear ratios in a transmision are found the same way. There is a gear ratio for each gear in the transmission, for example a five speed transmission will apply five different gear ratios to the output shaft of the transmission: first gear 2.315:1, second gear 1.568:1, third gear 1.195:1, fourth gear 1.000:1 and fifth gear 0.915:1. basically when you shift into a gear you are connecting the input shaft of the transmission to the output shaft of the transmission, this is how you get your gear ratios in the transmission, two different size gears in contact with each other. unfortunatly I don't know the gear ratios of any of the volvo trannys.If I knew the gear ratios for these transmissions I could answer your question a little better. If the transmission you put in your car has lower gear ratios throughout all the gears than the one in it now, you should get a quicker acceleration(shifting gears sooner)and you might notice an increase in fuel consumption but with the same final drive ratio you may lose some top speed or be at a much higher RPM say doing 65 or 70 MPH than you where before, it will be just the opposite for a transmission with a higher gear ratio than the tranny in your car now. All in all it really boils down to your final drive gear ratio witch is the gearset in the differential. It is real easy to get yourself into a bit of trouble when changing final drives, nothing like doing 70 MPH in fifth gear with your tach redlined. well, I hope this helped you a little good luck with your transmission swap.