Steve,

Thats a good question I have the same problem myself on my 240z it seems like the tach is in accurate. If you get the answer drop me an e-mail please

Eric 73 240z

 

I drive my 83 Turbo automatic at 75 mph (which is the speed limit on I-10 in Arizona) 110 miles round trip to work 5 days a week. It revs 4000rpm at that speed. The car is completely original and stock. The tires are the original size (205/60hr15) on the original 15x6 wheels.

The tach is correct. The car is geared fairly low because it weighs 3200 pounds and if it were geared higher, even the turbo model would not accelerate fast enough. I have never driven a 5 speed, but I would think that it has an overdriven 5th gear.

The auto really needs an overdrive, but 4000 rpm is not extreme for this engine. The biggest problem is gas mileage. I get about 20 mpg back and forth to work.(Not too bad for a car that will surprise V-8s) On a trip from Oregon to Arizona averaging 55-60 I did 26 mpg. (Takes a lot more horsepower to move the car up to 75).