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**Accelo** · 12-21-2021, 01:27 PM

Good point on the fan. A none OEM fan can add a lot of noise.
As we all have become accustomed to modern cars the typical motor RPM of vehicles the old cars and trucks, without overdrive transmissions, seem noisy because they are. If you had installed a modern automatic with overdrive installed the motor rpm would be closer to 2100 rpm. The early motor speeds seem ridiculous now days. You could change the differential or look for a stock three speed with overdrive for your truck. Frankly I am a little surprised there weren't more of these ordered back when. I did add an automatic overdrive transmission to a 1971 3/4T 396 truck I had. Increased the highway millage from 10 to 13mpg. a 33% improvement with no other changes. It quieted down the interior of the truck immensely.

BTW you would have to have a 2:61 rear end ratio to get the motor rpm down to 2100rpm with the transmission you have. It would be impossible to get moving on a hill. Yes, the overdrive is one of the best upgrades you can do in our old vehicles to make drive better and quieter.

12-21-2021, 01:27 PM	#4
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,358	Re: 3 speed RPM question Good point on the fan. A none OEM fan can add a lot of noise. As we all have become accustomed to modern cars the typical motor RPM of vehicles the old cars and trucks, without overdrive transmissions, seem noisy because they are. If you had installed a modern automatic with overdrive installed the motor rpm would be closer to 2100 rpm. The early motor speeds seem ridiculous now days. You could change the differential or look for a stock three speed with overdrive for your truck. Frankly I am a little surprised there weren't more of these ordered back when. I did add an automatic overdrive transmission to a 1971 3/4T 396 truck I had. Increased the highway millage from 10 to 13mpg. a 33% improvement with no other changes. It quieted down the interior of the truck immensely. BTW you would have to have a 2:61 rear end ratio to get the motor rpm down to 2100rpm with the transmission you have. It would be impossible to get moving on a hill. Yes, the overdrive is one of the best upgrades you can do in our old vehicles to make drive better and quieter.