The following information is based on my 54 truck which is driven every day....in fact, I just returned from the Turkey Run in Daytona, a round trip of about 300 miles. I am running a low torque cam, bored .060, a little head work, Fentons into 1-7/8 pipes, dual Carter/Webers and a stock distributor. The engine has been fully rotationally balanced, which I HIGHLY recommend. The transmission is an "85" T5 with a .72 OD and the differential is a Camaro 3.42 and the tire height is 28.5"
My 1960 235, makes it's power in this configuration between 1500-2400 rpm's. It cruises at 70 mph at 2100 rpm's and in 5th gear you can drop down to 45 mph in 5th and accelerate with traffic with no lugging. However, if you wanted to drop down to 4th gear it will comfortably wind to 65 mph at under 3000 rpm's. The truck will easily run 80 mph but has a sweet spot at 70 mph. Average mpg is 17.5 for both city and open road driving. My truck is still running a straight axle and 65-70 mph is the most comfortable cruising speed. At 80 mph the 4 wheel non-independent suspension becomes acutely obvious.
I tried a 3.08 diff which was totally unsatisfactory with my .72 combo. It made for a good 4 speed but lugged in OD at 55 mph and didn't "feel" right until you were at 70-75mph....too fast for comfortable cruising. The 3.42 is as tall as I would go with a .72 OD and a 28" tire. I would recommend a 3.42 as the tallest choice, with a 3.55 being a good option and a 3.73 if you live in a hilly region or plan on cruising at lower speeds.
Your first task is to determine your T5 OD ratio....the TAG on the front bolts will ID the year and a "search" will lock in your numbers. If your tag is missing, put the transmission in 5th gear, mark both front and rear shafts and rotate the rear output shaft 360 degrees. If the front shaft spins less than 270 degrees you've got a .72, if it spins more than 270 degrees you've got a .86 OD. If you by chance, have a .86 OD gear, you might be able to run the 3.08. I find the following site helpful:
http://csgnetwork.com/multirpmcalc.htmlThe lower calculator has proven to be very accurate.
My rationale, when building my engine and drivetrain was to maximize the original design potential of the 235. I saw no reason to try to spin a 4 main engine above and beyond it's capabilities and opted for a combo that lets the 235 breath and spin effortlessly, without a lot of unnecessary revs. I realize that pumping out horsepower and revs on a 235 is possible, but torque, economy and getting max. benefit for my bucks, made more sense to me. After all, the real joy of owning an AD is in driving it!!!! I hope this helps you sort out your options.
Dave
