5-6 MPG
 

My 1974 C10.

350 with automatic. No overdrive. I think a 3-spd TH350? I'll have to find the rear axle ratio...maybe 3:55/3:73.

I STILL thought I would average 10 or so mpg. I ran completely out of gas today. It took 16 gallons and averaging what I drove it last week is how I came up with the 5-6 mpg.

Would no overdrive and that kind of gear ratio = those numbers? Would it take a 3:23 or so rear to get 10mpg? I think the lack of a overdrive is what's killing the mpg?

https://i.imgur.com/FhlTmce.jpg

My Mustang gets 8mpg.

3.55 with a six speed.

Right foot controls mileage.

Drive into the lake or to a democrat run town. That mileage demands you take final action.

Unless you have a really steep gear which you'd notice you may have a leak. I've driven those for decades and never had that bad of mileage unless a BB 4x4 3/4 ton.
I drove the shit out of last one, had 373 gears and wasn't nice to it still got 12 to 15.

My 77 gets into the single numbers with the same 350/350 combo.
My full size truck can get about 20 mpg on the highway has the 5.3 6spd auto with 3:42 gearing rolling on twenty's.

Our C6 Z had the instant mileage in the gauge, it was a challenge to see how low i could get it. Had it down to 2 MPG A couple times :D

And you're bragging about that? :shrug:

that is what my old beater 74 ford gets. I still love putting around close by with it.

Those old Chevys are cool AF. It’s not your daily I assume so who cares what it gets.

The 900hp is the actual cause and my right foot is the variabe.

Perxactly.

My '70 big block vette gets about 10 mpg around town, about 14 on the highway. It sounds to me like there is something wrong with your truck.

That's about what I was getting with my '74 454 coupe.

I did a lot of both street and drag strip running. Back in the 60s I had a highly modified 67 Dodge RT 440CI auto trans.

Among the many mods were a rear end ratio of 4.33 and a Holly 3 barrel carburetor on a Eldebrock high rise manifold and a Mopar experimental cam.. That car did not get mileage it got yardage.

When it was stock it got like 12 highway and 9 in the city if you did not push it too hard. When modified like above it got about 8 on the highway and 4 in the city. Step on it and it got about 1 in the city.

Car was quite fast but even though I worked construction the gas cost was killing me I finely put in a 3.91 rear end and a Holly 3310 carb and it stayed that way for the next two years I owned it. Got married in 1970 and had to get a different car.

Ram 2500 4x4 with Cummins Turbo Diesel..... city/highway avg is about 24mpg. Straight highway trips I get closer to 27-28.

thanks

5 or 6mpg is indicating a problem...have you checked vacuum or rebuilt the carb yet?

The cure is better heads, 3.03 gears in diff. (if not already there).

If you want even better:
aluminum intake
carb spacer (for heat dissipation)
better cam
better lifters
2.02 heads
4 speed auto trans
3.03 gears in diff. (if not already there)

My '90 Chevy dually with a 454 gets 10.5 mpg city, highway, bed empty or loaded and/or pulling a trailer.

No problem. I'm only here to provide nothing of value. :cheers:

So important, he typed it twice.

I'm pretty sure my 'vette has 3.08 gears out back. That should give better mileage than 3.55, but nowhere near double the mileage.