gas milage

[cowman]

Was wondering what kind of milage could you get with a stock 283,stock saginaw tranny, and 3.73 gears. I want to keep my '67 as stock as I can so I;ll be running regular 7.00-15 tires.It's a lwb stepside. Also, where is that going to put me at RPM's at,say, 70 mph? 'prechate it.

[extd56]

Here is a good site to get an estimate. It looks like 3300 RPMS at 70

http://www.differentials.com/calc.html

[19673ontree]

that's the only thing about a 3.73 they run to high an RPM at highway speed
(70) as you said , my 67 is a 3.73 posi and about 55 is OK but 70 is buzzing my little six banger (LOL)

[piecesparts]

I put a 700R4 in front of my 3.73s (I also am running a smaller diameter tire than you guys--it is 27") and I am running 2500 RPM at 70 MPH. The tranny makes definite difference in RPMs.

[mnunn454]

In the early 70's I had 3.90 gears in my 283 powered manual tranny 1961 Apache stepside.

I once got 25MPG by keeping it under 55 MPH on the highway and taking off real slow at any traffic lights. Two biggest factors were the 16" military style tires that I had filled to 40 PSI (they were approx 36" tall and rolled like english racer tires), and the 283 had a tiny, early 60's Rochester 4-barrel carb (which for this trip at least only utilized the primaries). The 25% taller tires reduced the final drive ratio to about 3.0:1 and the tiny primaries did a great job at metering the fuel like a miser. Most of the time though I got around 15MPG with it "in-town".

I'd think 15 to 17 MPG is a reasonable expectation with yours if you'll go easy on the gas at stoplights, run the tallest reasonable tire, and pay close attention to carb jetting to keep your average air/fuel ratio in the 14.5 to 14.7:1 range using an O2 sensor and an A/F ratio gauge.

Hope it helps.

[gkolmatycki]

Just to give you an idea.....Right now I have a basically stock 283 with a quadrajet, rebuilt TH350 tranny, 235/75/R15's & a 4.56 gear ratio in my rear end. I get about 12-13 MPG. And it revs at about 3850 RPM's at 70 MPH.

[cowman]

Thank ya'll for the info. I've been around these old trucks all my life,but I've got a lot to learn about the machanics. But, now ,if any of ya'll have trouble getting your cow to milk, just drop me a line.