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**Accelo** · 10-12-2022, 11:37 AM

On a stock 396 with 4:11 gears (3/4T) an overdrive changed my mileage from 10 to 13 on the highway. A 33% increase! No much difference in town. However the difference in the sound level in the cab made it worth it. I don't believe you could add enough insulation to make the same difference the reduced rpm of the motor made.

10-12-2022, 11:37 AM	#5
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,358	Re: 67 truck info stuff On a stock 396 with 4:11 gears (3/4T) an overdrive changed my mileage from 10 to 13 on the highway. A 33% increase! No much difference in town. However the difference in the sound level in the cab made it worth it. I don't believe you could add enough insulation to make the same difference the reduced rpm of the motor made.