RPM & Gas Mileage: Effects on Overdrive Vehicles

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RPM significantly impacts gas mileage in vehicles with overdrive. An example is an '82 Buick Riviera, which achieved 26 MPG on the freeway at 1500 RPM while traveling at 70 MPH. In contrast, two 1968 Chevys with carburated 327s only managed about 17 MPG, with RPMs at 2400 for the model with a 2.73 rear end. The difference in rear end ratios also contributes to variations in fuel efficiency. Understanding these factors is crucial for optimizing gas mileage in overdrive vehicles.
Greg Larsen
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I was reading a post about the effects of RPM on gas mileage, It was from 2007 so I couldn't reply to it. RPM does make a difference on gas mileage when it comes to overdrives. I had an '82 Buick Riviera with a small block engine with an overdrive and a quadrajet that got 26 MPG on the freeway and about 21 in the city. I now have two 1968 Chevys with carburated 327s that only get about 17 MPG. One had a 2.73 rear end and the other a 3.08. The RPM on the Riviera going 70 MPH was only 1500. The '68 with the 2.73 was about 2400.
 
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