i know muscle cars benifite from a new rear end ratio but what about 240's? do we not have enogh power to change our ratio and make it run right?

any car that has enough power would benifite from a new rear end ratio, i dont think it would do much on a stock 240, but if the car has decent power sure it would

yea i got a lower gear ratio....so my top speed is harder to get to....

how can you change it? is there a kit?

just replace the rear diff not really a kit. you can use a 300ztt lsd to drop down the ratio or others I'm not sure.

it is the gear ratio in the rear "pumpkin"...

will it be okay with an auto trannie? or will i mess it up really bad? is it worth the work also?

shorter gears would help out quite a bit with an auto, since you cant really slam it into a lower gear when you need power... basically the shorter rear end gears will take you through each transmission gear faster, so with a stick you are shifting a lot more, but with an auto it will do all the work. if you have added HP, id say it would be maybe .5 sec quicker in the 1/4...just a guess. on my friends old saleen it had real short gears like 3.55 i think and that was a huge difference over other mustangs.

You need power to keep numerically lower diff ratios, if your diff is 3.55, that means your crank/pinion gear goes 3.55 to the ring gear of the diff. So for powerful cars the ratio is numerically smaller, but actually, the gearing is taller, this helps you stay in that gear longer, and result is less shifts.
The diff ratio is the drive shaft to the big ring gear that is spinned by the pinion gear. That is why if you have alot of power, like the small block powered bikes, they only need two gears.
shorter gears would help out quite a bit with an auto, since you cant really slam it into a lower gear when you need power... basically the shorter rear end gears will take you through each transmission gear faster, so with a stick you are shifting a lot more, but with an auto it will do all the work
I can't seem to understand what he means.

simply put, power has nothing to do with rear gear ratios

if you get one with a higher number, or a lower gear as they say... you will accelerate faster, no matter what power you have. If you go with a 10% increase in gear ratio numbers, you will see a 10% increase in acceleration....also a 10% decrease in top speed.....

they work with auto's, manuals, herses, ambulances, and even ice cream trucks

just replace the rear diff not really a kit. you can use a 300ztt lsd to drop down the ratio or others I'm not sure.

A Non-turbo 90-96 300ZX has the same 4.083 gearing as a 240SX, so you aren't going to get lower gearing, however, the 300ZX dif is a VLSD. Its basically a limited slip differential that uses pressure from heated fluid to lock the force the two axles to turn rather then a clutch pack. Its not instant like other LSDs but doesn't try to push the car straight when you're going around a corner like a spring loaded clutch LSD does and it does work surprisingly fast. You can find good condition 300ZX difs for $150-200.

If you get a rear dif out of a Twin Turbo 300ZX, you'll be increasing the overall drive ratio because the turbo gears are 3.692.

Here is a good place to screw around with different gear ratios. (http://www.geocities.com/z_design_studio/transmission_300zx_tt.html)

And just for FYI.

240SX 5spd
1st 3.321
2nd 1.902
3rd 1.308
4th 1.000
5th .759

240SX Auto
1st 2.785
2nd 1.545
3rd 1.000
OD .694

^^^are used lsds really that cheap???

hmmm...that gets me thinking

Check wholesale wharehouses and wrecking yards. The only problem with the 300ZX is you need different flanges to hook up to the axles so it may be cheaper to find one from a 240SX that had a factory LSD.

Here is a more complete reference (http://www.240sx.org/links/installs/lsd/lsd.htm)