I am wondering what maximum mileage/lt and speed I may have with my 71 240z with 5-Speed (82-83) transmission ?.

Many things vary for this answer , condition of the power plant and tuneing as well as rear end gearing and wheel and tire size. I would say though that the max mileage will be about 23 MPG give or take a mile or two. With a L-24 engine top speed at about 100 MPH . Your top speed will be dictated by the HP of the engine and gearing. If your gearing is to low the engine will be past it's power rainge at a lower MPH . If the overall gearing is too high the engine will not be able to attain the enough RPMs to reach the power range. With the proper gearing for the horse power of your engine all this will be in ballance and on the level , I still think 100 to 105 MPH. Gary I hope to visit your country soon . My Wife and her Sister toured there a few years ago and had a wonderfull time. All the best to you and yours.

I made 105 mph several times,however,that was for testing only and I try not to drive above 90.The funny thing is other drivers looking with a look of expectation of higher performance from such a car since there is no other 240Z that I know around here.

It looks like my mileage is 12 mpg,which is very low.I know that my carbs are running rich but I have to work on them more for better tuning.

Let me know about if you decide to visit .

Thanks