Join Date: Feb 2003
Location: Nashville, Tennessee
You are correct, at 70 MPH with a 2.56 rearend gear in 5th at 1 to 1 ratio you would run 1825 RPM with a 33 inch tall tire according to the calculator on this site. Poor memory on my part.
At 70 MPH you will ONLY run 2150 RPM with a 2.56 rearend gear in 5th at 1 to 1 ratio with a 28 inch tall tire. This is still as good as many overdrive options available out there. None of the "new" overdrive transmission options are as economical as a good used 5 speed Nash install to replace the stock 4 speed.
Most modern overdrive options require a 3.42 or lower rear gear to make them happy in overdrive and not lug the engine. Therefore you may have to change the rear end gear. I have personally seen far more 3.08 or higher rear gears in Chevelles than I have seen 3.42 or lower gears in stock rearends. Either way, a rear gear change may be needed. 2.56 rear gear 10/12 bolts are a whole lot cheaper than 3.73 rear gear 10/12 bolts in you are buying a rearend to swap in your car. Changing just gears in the rearend will cost the same if buying new gears for the swap. I have personally purchased complete rearends with 2.56/2.73 gears because they were cheap as "most" folks have no need for those gears.
Again, just another way to make your Chevelle more drivable for less money in comparison to "Gear Vendor" overdrives and their install problems, Keisler Tremec 5 speed Transmissions and their cost,, T-56 cost and other alternatives. Most of these options require floorboard surgery to make them fit your car.
Is a Nash the best option avaiable? NO! If the end result driveability, less expense and less install hassle are part of the equation, it certainly is something to consider. It's not glamourous and will not make the magazine write-ups, but that's never been important to me. Ride and drive is what's important!
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Remember, "Drive Fast, Turn Heads, Break Hearts"!