C1 Gas Mileage!

[Bob B.]

Hi all,

My 1960 has the original 283/230. It had never been apart and got 16+ MPG when I got it. It is now completely rebuilt, and the rear axle is now 3:08 (was 3:70) for highway driving, and the trans is wide ratio. My first check is showing 13 MPG! Any ideas on the cause of the drop but, more importantly, what to do to bring it back up?

Thanks,

Bob

[Jim K.]

Re: C1 Gas Mileage!

Just a quick thought, with the 308's, the speedo 9and odometer) are not reading accurately. Plus fresh rebuild is a tight motor that will "loosen up" in the next 1000 miles... just my quick $0.02

[Wayne K.]

Re: C1 Gas Mileage!

Bob,

As Jim has mentioned if you didn't correct the transmission gear for the rear axle gear change your speedo is reading slow and your odometer is short on actual distance traveled.

Wayne

[Doug Flaten]

Re: C1 Gas Mileage!

Did you change the speedometer drive gear to the correct ratio for the 3.08?
If not, I'm afraid that 16% difference in the rear axle ratio would not account for all of the 3+ mpg decrease. However, the speedometer gears are never dead on. And about all you can expect is to be within 5% accuracy. Tooth count of the speedo gear is around 18 to 22 if I recall and changing by 1 tooth increments results in changes of 5.5% to 4.5% respectively.
The other possibility is that your 3.70 axle setup may not have had the correct speedo gear to start with and you could be comparing against an invalid number.
Doug

[Verle R.]

Re: C1 Gas Mileage!

Bob,

You should consider what is said above as a start.

I would also take a look at the carburetor and ignition system.

Float setting, correct jets, proper operation, make sure the choke is retiring completely.

Proper function of the distributor and correct timing will have a lot to do with MPG.

You should be getting about 20 MPG or so with the 3.08 gear if everything is right.

Verle

[Jimmy G.]

Re: C1 Gas Mileage!

Tighter internal engine parts. My old 1960 270 HP engine after rebuilding from a turned rod bearing is much tighter and therefore more internal friction that robs power and milage. I suspect the same with yours. It should get better as the engine breaks in. I went a long way to that end by running 5000 - 6000 + RPM in third gear around Lowe's Speedway in April.

[John D.]

Re: C1 Gas Mileage!

Jimmy, Course u is pulling a heavier load. JD

[Bob B.]

Re: C1 Gas Mileage!

Thanks to all! I did over 2K miles to and from Boston and calculate my average as 19.11 mpg now for the whole trip, so it looks like things are probably about loosened up. Yes, I do have the right gears and all. MPH and odometer match almost exactly with my wife's Saturn. - Bob