Trans Decision

[BigDan3131]

So here is my dilemma, I have a 1965 GMC long bed fleetside 3/4 ton that after removing unneeded weight and going to a glass hood. I plan to run a tire near the stock height of 31.5" but with 18" rims, I think I have talked myself into going with a TH350 instead of the TH200R4 because based on how much it would cost to build the OD trans plus the cost of the new convertor I can do a ring & pinion swap to 3.54 gears and keep the 31.5" tires. Since I'm trading my bodywork skills for an engine build I figure that a 6.0L with a cam swap and the usual speed goodies my lack of gear will be made up for it with the power I make at my cruising speed [70] down the freeway.

Comments?

6.0L with Dual 450 Carbs.

[Shorty63]

2600 rpm at 70mph, seems like a decent set up!

[kieth]

A rear gear swap is easier than a transmission but the fuel economy of a OD transmission sure make one stop and think about which way to go. If you are going to use your 3/4 ton to pull trailers etc you might look for a 4L80e transmission. this would give you lower rpms while driving normally cruising at 70, and then you could shift to direct and have loads of pulling power. The gear we see most often with this combo with a really tall tire is 3:73 but your 3:54s would also work. Send me a private message on this board and give me the following items:

1. engine hp, model etc.

2. tire diamater 31.5"

3. E MAIL ADDRESS

and I will send you a spread sheet that shows usable torque to the ground and speeds at 1500, 2000, 3000, and 4000 rpm. With this info you will be able to see how much torque you will be putting to the ground with most transmission and rear end combinations. (Torque within a usable range of speeds)

AND SEE MORE CLEARLY THE IMPLICATIONS OF THE CHANGES YOU ARE MAKING. i.e. keep from having a truck that will not get out of its own way or one that does not get good fuel mileage.