Towing w/ 72 3/4 ton

[Mertz]

I have the 350 running as well as possible. I have a Cliff Performance Qjet on an Edelbrock intake with MSD ready to run ignition, 1.5 roller tip rockers with correct geometry on the push rods, ceramic headers with proflow dual exhaust with cross over pipe. Timing is at 36 initial plus mechanical all in at 2500. The 350 trans has a shift kit and was recently rebuilt. Tires are LT24575R16. I am pulling a 5000lb trailer and it pulls ok on the flat but has to really work hard to get it up a long 7% grade. I believe my rearend has 3:08 gears. Would going to 3:55 or 3:73 help without loosing too much gas mileage when not pulling. I am getting 15mpg now. I only pull the trailer twice a year.

[68350]

A steeper gear ratio will reduce your gas mileage, by how much I'm not sure. Are you sure you have 3.08 gears? They were not offered in a 3/4 ton in 72, the numerically lowest would have been 3.54's. 3.73 or 4.10 will help pulling, but I'm not sure the switch would be worth it considering you only pull your trailer twice per year.

[mrein3]

In my opinion the perfect set-up for your application would be a 700r4 transmission and 3.73 rear end gears. The two times a year you tow that big trailer leave the transmission in 3rd gear. The rest of the time you'll get similar mileage to what you are getting now.

Expect 10-13mpg with a th350 and 3.73 rear end gears.

[Rodk65]

Just my opinion but if it isn't broke why mess with it. It sounds like you have a good set up and are getting good fuel mileage. Any change you make is likely to drastically change your gas mileage for a trailer you only pull twice a year.

[Longhorn Man]

what rear end are you running to get that gear?

[BB72CHEVKT]

If I only towed twice a year I would leave it alone as well.

[Mertz]

Not sure about the 3.08. I will check the numbers to make sure.

Would lower tires help?

[capev86]

a 3.07/3.08 is great if you have a big engine, diesel, don't tow and use your truck for highway commuting only.


a 5,000 pound trailer is a pretty sizable load to be pulling up through the hills. a 350 is a pretty stout engine. if you did more towing a 383 would be an even better balance of torque and fuel economy. you are on the right track with the q-jet as they have good low end response and economy with high end peformance when needed. only thing better would be an aftermarket tbi style induction with mpi fuel rails. remember that a carb can not adjust to altitude like fuel injection can. that was the problem with a trip out to yellowstone with our 6000 pound camper. steep grades and high altitudes can make it very difficult, even when you have over 400 cubic inches of pumped up small block under the hood. remember that max tow ratings are optimal on relatively flat roads.

put an overdrive in your truck and you will love 60-70mph cruising and getting good gas mileage. the 700-r4 has a more aggressive first gear that is great for towing while the 200-4r has a slightly better overdrive ratio (.67 instead of .7). the 200 is a great general use, nearly bolt in swap for a t350 (just move the cross member back to the next hole?) and does not require you to shorten the drive shaft.

my bet is that you may have a 4.10 in your truck or 4.11 if it is a dana 60 as that is a small block and not a big block. you mileage can also be dependent on your driving habits. i was getting no better than 11 mpg in my 72 burb c20 w/ 307 3 on the tree (solid lock-up so no wasted rpm's) and 4.57 rear. with a 4.10 swap i now get 13mpg.

3.54 x .7 o/d = 2.48
4.10 x .7 o/d = 2.87
4.57 x .7 o/d = 3.20

my dad's trucks - highway mpg:
72 burb c10 305 q-jet t350 3.73 = 15mpg (77 305 w/ stock 72 carb, rv cam)
84 burb c10 350 q-jet 700r4 3.73 = 18mpg
84 burb c10 406 q-jet 700r4 3.73 = 17mpg (after engine swap)
87 burb c10 350 tbi 700r4 3.73 = 18mpg
99 burb c10 350 tbi 4l60e 3.42 = 22mpg