2.73 to 3.42 swap, Fuel milage? Please help

Here's a couple of calculators.

http://www.wallaceracing.com/gear-speed.php

http://www.race-cars.net/calculator...calculator.html


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__________________
''Life's tough, Pilgrim, and it's even tougher if you're stupid.''---John Wayne

Midnight Sun Street Rod Association

Thanks again for all the help guys! i apreciate all of your input! I think what i may end up doing is putting a set of 3.36's in, and if its revving too high for me on the highway, later in the year i could find an overdrive to stick in to compensate. What would be an easier swap? a 700 or a 200?

I had a similar question awhile back and went with 3.42s based on responses I got here. This is a 10 bolt posi I was rebuilding to replace a 2.41 10 bolt posi I had under my 54 Chevy truck with a 355/TH350.

I drive the truck daily and found that while the performance was much improved off the line the cruising RPM turned out to be higher than I am happy with. I was getting 18-20 MPG previous and now am lucky to average 15 MPG in daily commuting.

If I were to do it again I would choose 3.08 gears for a street driven setup unless you change to an OD transmission. Then the 3.42 would be fine in my opinion.

I'd keep your current gears and do the trans swap first.

If you want to do an OD trans and gears then going with a 3.73 rear gear and either a 200r4 or a 700r4 will be fine. Without the OD the gears will be a pain in the ***, and with your current gears the OD will make your engine lug alongnad can create a lot of problems. a TH350 and 2.73 rear gears is fine for cruising on the highway and if its a healthy engine you will have no problem around town. You can also step the stall up a little (not too much though with 2.73 gears) if you want more pep off of a stop light.

much cheaper to put in a th350. And would yield much better results

first gear in a th350 is 2.52:1

first gear is a 2 speed is 1.70.

so installing a th350 would be like putting in 4.04 gears in with the 2 speed (in first gear).


2.52 x 2.73 = 6.8796:1 would be the 1st overall ratio for the th350 with a 2.73 gear.

1.70 x 4.04 = 6.868:1 would be the ratio with 2 speed and a 4.04 gear in 1st gear.

top gear would remain the same.

2nd gear in the th350 is 1.5:1 (almost like 1st gear in the guide)

Actually, someone posted the chart online, so i just link to it:

http://www.wallaceracing.com/reargear.htm


It's copywrited stuff, so i have mixed feelings.............