Transmission upgrade and Drive line Advice

[JohnnyPopper]

You guys with numbers at the ready just kill me

Thanks EJ! Very Helpful!

From the time I had my first truck, I was told that your fuel efficiency was best at your max torque RPM point. Any truth to that?

I know there are variables that affect each outcome, just wondering if is true or urban legend?

[ehjorten]

Johnny;

Lowest Brake Specific Fuel Consumption (BSFC) occurs at or around peak-torque. That is where the engine is the most efficient with the use of fuel, but usually this does not coincide with the best fuel economy for the total vehicle because of variables outside of the engine like aero drag and rolling drag.

Typically for best fuel efficiency you want to aim for the lowest RPM that keeps the converter locked-up.

[JohnnyPopper]

EJ that makes the most sense to date. Thx!

My gut told me that if your RPM is at its highest torque level, then ebbs and flows of torque demand would be in a sweet spot. I mean, your engine is offering the most it can in that range.

Having said that, I guess it's simply a math equation that determines mass/RPM of any given engine spec.

My first truck, "57 Apache 3100 had a 235 CID that developed max torque at 2000 RPM. Pretty slow in the late '70s. OD made quite a difference...

With your calculations in this tread, I will try to determine the max torque of my motor, and try to pin the gearing to stay in that range in my 65 mph cruising.

[ehjorten]

Johnny;

I would say 35's and 4.11s, but that means having both front and rear gears re-done, which isn't inexpensive. Couple that with switching over to an overdrive transmission and mating it to your transfer case. It is gonna cost you a pretty penny and it will never pay for itself, but it will make it a much more enjoyable truck to drive and you might be able to recoup some of the investment later down the road, selling it.