From the original owners manual for a 1972 240Z, it indicates that first gear max. mph is 38, second gear is 60 mph, and 3rd gear is 95 mph. My Z's first gear is winding out at about 15mph, my second is 33 mph, and third is probably around 55 0r 60 mph. It's at the point where I don't use the first gear. What kind of gear speed range are others experiencing?

Are you running a standard 4 speed box and 3.54 diff?

Yes, it is the standard four speed transmission. I'm not sure about the differential except that it is limited slip.

Well, if you have a limited slip in your car, then the differential is definately not the original. It would be an open 3.36 if it were the original. It's possible you know have either a 3.90 or a 4.11.

You can check it out on the gear calculator if you know the RPM's you are turning.

Try this: www.geocities.com/z_design_studio/

As I understand it, the higher the gear number, the more teeth and thus larger gear diameter. So the limited slip has a larger gear diameter than stock differential?

After further investigation, I believe that I have a 4.11 differential ratio. I plan to use this car as an everyday driver, so I am thinking about changing the ratio back to a 3.364. Currently, I am not using first gear for normal street driving. If I swapped out the differential to a 3.364, I believe that I would start using first gear again, making up for any acceleration lost with a 4.11 diff. in second gear. Does anyone have an opinion?

If you aren't worried about killer performance off the line, the 3.36 is a fine ratio. And you will get better MPG and lower RPM while cruising. Is your 4.11 a limited slip? If so, would you like to part with it? Do you have a 3.36 to replace it with?

Thanks,

Rick

It is a limited slip, and I think I'll hold on to it. My plan is to keep the limited slip and replace the differential gears.

After checking on the parts cost to swap out the 4.11 to a 3.364, I think I'll go to a junkyard that has a 71 240Z and see if it has the 3.364 rearend. If it does, then I would be interested in selling the 4.11 limited slip rearend.