Gas mileage

[DdowC20]

Right now I have a c20 with a rebuilt 350 and a 2 barrel factory carb. I pull trailers fairly regularly and was hauling two horses in a steel bodied trailer the other day and really didn't have a lot of problems. The thing pulls like a champ. However, I was running secondary roads and it did dog down in the hills. I dropped from about 60 down to about 47-48 going up a couple of hills. I know that if and when I go on the highways, there are some hills that would just cause problems. My question is going to a 4 barrel carb to increase power. I have thought about regearing the rear end but don't want to lose any low end. The truck has a four speed with a granny gear. The tag for the rear end is missing so I am not exactly sure what it has for gears. So my question is, given that I have supplied limited amount of information, how would a four barrel affect gas mileage? Right now empty I am getting around 14, sometimes 15 mpg. Hauling the trailer I got about 11. I also haul a 6x12 box trailer a lot and get about 13 mpg with that. I guess my real question is am I going to lose mileage, as I think I will, and will the additional power be worth losing mileage? Thank for any thoughts.
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[Swar]

I'd say leave the engine alone as long as it's running good. Your mpg is decent for what you're doing with it. A 4 barrel is going to suck down a lot more gas.
You should try to find out what ratio you have now, and look into swapping for a lower one. 4.11 is great for hauling/towing, as long as the transmission's top gear allows for highway speeds.

[MagmaJct]

AFAIK I have a bone stock 350 on my C10 with the exception of the Edelbrock 1405 (Carter AFB) with automatic choke upgrade. I have yet to break 10 MPG. Uphill, downhill, loaded, unloaded, pulling a trailer, not pulling a trailer.

But my engine has chronic low vacuum at idle. In drive the vacuum is 10 in/mg. I have upcoming plans to pull the timing cover and inspect the timing gear for wear and a possible jump. I wish I could get 14 MPG!

Once I get the low vacuum resolved I can try and get that Quadrajet I got off eBay working.

Regards,
Mike

[In The Ten Ring]

Originally Posted by Swar

I'd say leave the engine alone as long as it's running good. Your mpg is decent for what you're doing with it. A 4 barrel is going to suck down a lot more gas.
You should try to find out what ratio you have now, and look into swapping for a lower one. 4.11 is great for hauling/towing, as long as the transmission's top gear allows for highway speeds.

Based on what your last sentence states, how would a 4.11 with 3OTT fair towing?

My truck has a tow hitch but has never towed anything in its 42 years on Earth. I do plan to use the hitch at some point and I'm curious how that will go. It's a 1972 with the 250 I6. (4.11 with 3OTT).

[special-K]

A 4bbl will give you better mileage when cruising on the primaries. It will give more power and suck more fuel when taking on those hills. Worse mileage when you need the added power/better mileage the rest of the time. I am talking spread-bore 4bbl, such as came on these trucks.

[Grumpy old man]

I have a few extra stock small block 4 bbl intakes and quadra jet carbs if anyone needs them cheap.

[Swar]

Originally Posted by In The Ten Ring

Based on what your last sentence states, how would a 4.11 with 3OTT fair towing?

My truck has a tow hitch but has never towed anything in its 42 years on Earth. I do plan to use the hitch at some point and I'm curious how that will go. It's a 1972 with the 250 I6. (4.11 with 3OTT).

Sounds like it could haul and tow no problem. Inline 6 cylinders are known for decent low end torque. 4.11 is low for a 3 speed, I'm guessing it screams at 65 mph and likes to do 40?
My truck was originally a 250 6 cyl with a 3OTT (short bed) and even with a higher ratio in the rear, it could haul no problem. I don't even know what my ratio is, probably 3.42, at 60 mph, the rpm is at 3k.