I am running 4 grand at 65mph?????

Hello i have a 1971 nova with a 350 and a turbo 350 trans with 1.50 gears in the rear end. when i am crusing at about 65 miles per hour the tach reads 4000 rpm, and its not the tachs fault because it sounds really wound up. i can't figure this out. i need your help.

I'll assume the transmission is going into 3rd gear for now. Is this a new combination or a new ride for you? There is no such thing as a 1.5:1 ratio rear.

If you want to see what ratio you have, jack up the rear end, put the transmission in neutral. (Use jackstands!) Put a chalk mark on the driveshaft, close to the rear yoke. Put another chalk mark on the inside of the tire where you can see it from under the car.

See how many rotations of the drive shaft it takes to get one rotation of the tire (rotate it by hand with the engine off). For example, if it takes 4 turns of the shaft to get one turn of the tire, your rear is a 4:1 ratio. There are also online calculators that will help you, measure the circumference and or diameter of a tire, you'll need it.

Bob