[Kendall03]

I have a 1939 Chevy. I am running a 350/290 hp carburated engine. I have a 600 cfm Edelbrock carb, 350 trans and a 274 rearend. My question is if I put a 700R trans in with the current set up will it increase my gas mileage? I have been told that it would and I also have been told that the rearend is way to high and it will more than likely be worse. Does anyone have some ideas as to what is the best set up? I would like to try and get around 20mpg. Right now I can get about 15 to 16 at hwy speeds. I have talked to a lot of street rodders that drive as many miles as I do (15,000 a year) and they have told me that it is possible. But as you know and I know a lot of people don't always tell the truth. Thanks for your help.

[Blazin72]

The .70 overdrive in the 700R4 is going to give you a 1.92 final drive ratio, which is very high. I honestly don't know that I'd go with a final drive ratio any higher than what you already have.

If you swapped in 3.92 gears with the 700 you would have the same final drive ratio you have now but much better acceleration.

If you swapped in some 3.73s you would end up with a 2.61 final drive.

PM Berlinerbelair. He's been working on an old (58?) Bel Air with a 283 and he's getting pretty good mileage for a V8.

[SSedan64]

I agree, you don't want an O/D Trans with 2.74 rear gear.
You want to have the rpm high enough to prevent engine lugging, while in 4th/OD and keep the Carb out of the power enrichment circuit.
3.42 gear w/700R4's .70/4th may work better for mpg = 2.40
3.23 w/.70 = 2.26
How heavy & aerodynamic is the 39?
A QuadraJet carb would be best but, the Eddy may have some more mpg in it if properly tuned with a A/F rato meter.

[dalesy]

I'm kinda surprised you aren't gettign better mileage, with that rearend. Like said above, I'd suggest some more 'professional' tuning. Could be too big jets, wrong intake manifold...who knows?

I dont' think your car is real heavy and your engine isn't radical...try some research first.