different gears or bigger tires?

[Family Truckster]

I have an 88 1 ton dually bonus cab (older style), 454 TBI, T400 Trans and 4.10 Gears. 215/75/16 tires in the back.
I'm pulling a 3500 lb boat a few times a year and a 28' fifth wheel camper twice a year. I was thinking of pulling them both at the same time. I also might be hauling some dirt and gravel from time to time.

Don't laugh but I'm looking for a little more efficiency, I average 7MPG right now. Would taller tires such as 265s or 285s be a better option than switching to 3.73 gears? What about doing both tires and gears?

[gchemist]

Welcome to the site. Torque peak on the motor is important. Different gears and tires may not matter if peak torque is not used properly. Even deeper gears may be you getter gas milage!! Do you know the cam torque curve?

[Family Truckster]

Unfortunately no, but I've read about certain pickups needing that higher RPM to maintain ultimate efficiency. I don't have a tach but i found a calculator, http://www.markwilliams.com/calculators.aspx, that allows me to plug in different tires and gears. Thats what got me thinking.

[gchemist]

Yes, BB like higher RPMs for torque. Other changes may help. Headers, cooler thermostat, carb tuning, and good tune up are good things that help efficiency.

[Family Truckster]

Thanks!
I'm sure my pickup is running right where it should but where can I find my peak torque?

[gchemist]

You need a factory spec book or info on that year model. HP is low from the factory. HP is up in the RPM range. Max torque peak is at 5200 RPMs. Most starting point charts for torque is 1500 RPMs.

[Edahall]

Originally Posted by Family Truckster

I have an 88 1 ton dually bonus cab (older style), 454 TBI, T400 Trans and 4.10 Gears. 215/75/16 tires in the back.
I'm pulling a 3500 lb boat a few times a year and a 28' fifth wheel camper twice a year. I was thinking of pulling them both at the same time. I also might be hauling some dirt and gravel from time to time.

Don't laugh but I'm looking for a little more efficiency, I average 7MPG right now. Would taller tires such as 265s or 285s be a better option than switching to 3.73 gears? What about doing both tires and gears?

Your greatest loss in efficiency is the T400 transmission in your truck. It's a tough transmission but the parasitic loss is quite high mainly because the lack of a lock up torque converter. If you want to fix that, there are several options. The best would be to install a NV4500 5 speed manual or an automatic transmission such as a 4L80E. The other option is to install a low stall torque converter in your T400. It would decrease the parasitic loss but at the expense of some power. It would also lack having an overdrive.

[donut]

I really haven't looked into the mileage, but with a BB you can't really expect much.
Free flowing duals would help, if it come equipped that way.
Cam change? Don't know what would be computer friendly.
My '86 does run with 235/85-16 tires, as far as I can tell it's been a tow mule most of its life. What I did find out is the stock replacement torque converter was rated for about 1300 stall (low). Truck hasn't been on the road enough to clock the mileage.

[andrewmp6]

Tires won't give enough change i would look in to a diesel swap and trans to see the most mpg.