Highest MPG V8?

[theholycow]

Originally Posted by dkjones96

You know you'd want one!

I'd consider it, but I don't think they exist. Was that a flight of fancy, or do you know something about a new RWD model?

[BeerDaddy]

Help, I am restoring a 85 GMC C3500 1-ton Bob Tail Flatbed Dually, with a HD 350 V8 four bolt main, 400 Turbo Automatic Trans with overdrive, 4 bbl Rochester Quadajet no computer. It is currently only getting 10 mpg in city, 12 mpg on highway while empty with no trailer or load. Replaced distributor with a high performance HEI distributor, new fuel pump, new fuel lines, rebuilt radiator(s), and new tires. I am looking to get mileage up to 20+ Highway, will replacing Roch Quadajet carb with a more fuel efficent carb work or should i just buy a rebuilt Rochester Quadajet and change the rear end gears and a different Overdrive in transmission?

[theholycow]

The Quadrajet, if it's not the most efficient, is one of the most efficient carburetors ever to hit the mass market.

I always support efforts to improve fuel economy in any vehicle and try not to be a naysayer but I don't think it is realistic to look for 20+ highway in a 1-ton dually 1985 model. I doubt you could manage it even with a modern small turbo diesel and a manual transmission, let alone a carbureted 350 gasser and an automatic. There are probably things you can do to improve it but I'd be surprised (and happy!) to see you hit 20.

Since you're asking about gears, how's highway RPM and power? If it's already downshifting to get up hills then it's probably as tall-geared as it can use.

[Jay2TheRescue]

If you get that to 20+ on the highway, it will be geared too tall to load that vehicle to capacity. I have owned several trucks of that style/vintage and only one of them gave me over 20 MPG highway. It was a 1974 Chevy C10 1/2 ton 2wd. It had a small block 350 TH350 3 speed automatic transmission with locking torque converter. I had replaced the points type distributor with an electronic distributor I got out of a junked 1975 van. I used to get about 25 highway in that truck, but it was light, and I drove it with a light foot. The best I ever got on the highway in my 86 Chevy C10 (which has a small block 305, T700R4 4 speed automatic with locking torque converter) is about 18 highway. My 1998 GMC K1500 extended cab has a 350, fuel injection, 4 speed automatic with lockup, and 4wd. The best I ever got out of it was 18 MPG, and that was on ethanol free fuel, going 70 MPH fully loaded on the highway. My 2000 GMC Savanna 3500 gets me about 16 highway, and that's a 1 ton with fuel injection, 4 speed automatic, etc.

To have any hope of getting a 1985 1 ton to hit those numbers, you will probably have to convert it to a 1/2 ton truck (you can't haul the heavy weight anymore). Take the E rated tires off, change the transmission, rear end, shocks, springs, and lower it to the 1/2 ton height.

Brand new 1 ton trucks don't hit those numbers unless you're looking at diesels. IMHO, with what you're gonna have to spend, (and then have a truck that won't haul the weight) it would be cheaper to just find a nice used 1 ton with a turbo diesel.

[sk6strng]

My commuter car for work is an 86 Honda Civic si hatchback (1.5 w 5-speed manual trans, 200,000 miles on the odometer). I drive this car light and dont wind up the revs, also have plans to swap out my 5th gear to the 85-88 crx hf 5th gear (taller) to drop the overdrive rpms for better fuel economy.

Going for high efficiency in this car is to compensate for my 56 Belair 9 passenger wagon.

The wagon is a brick. It runs a 1970 vintage Corvette 5.7 litre v8 and 700 r4 overdrive trans into a 2.73 rear gear. (Headers and dual exhaust)
I am running Michelin Primacy x 245 series tires meticulously kept at 35 psi.
I guess that this 57 year old car gets quite poor fuel economy...dont know for sure since the speedometer is inoperative. The engine turns just under 2000 at 70 mph.
But check this out...The car is generally used with three or more occupants in it, often upwards of 6 people with my two 9 year olds and their friends.

It does merit mentioning that if this car did not have three rows of seating many of my weekend car trips would require two vehicles and two drivers.

Any tips for saving fuel on the wagon are always welcome (comedy appreciated)..
Thanks and have a great day!

[Jay2TheRescue]

Originally Posted by sk6strng

My commuter car for work is an 86 Honda Civic si hatchback (1.5 w 5-speed manual trans, 200,000 miles on the odometer). I drive this car light and dont wind up the revs, also have plans to swap out my 5th gear to the 85-88 crx hf 5th gear (taller) to drop the overdrive rpms for better fuel economy.

Going for high efficiency in this car is to compensate for my 56 Belair 9 passenger wagon.

The wagon is a brick. It runs a 1970 vintage Corvette 5.7 litre v8 and 700 r4 overdrive trans into a 2.73 rear gear. (Headers and dual exhaust)
I am running Michelin Primacy x 245 series tires meticulously kept at 35 psi.
I guess that this 57 year old car gets quite poor fuel economy...dont know for sure since the speedometer is inoperative. The engine turns just under 2000 at 70 mph.
But check this out...The car is generally used with three or more occupants in it, often upwards of 6 people with my two 9 year olds and their friends.

It does merit mentioning that if this car did not have three rows of seating many of my weekend car trips would require two vehicles and two drivers.

Any tips for saving fuel on the wagon are always welcome (comedy appreciated)..
Thanks and have a great day!

Welcome! I'd say if you have a 350 V8 that's turning 2,000 RPM @ 70 you're probably doing 18-20 MPG. Considering what the car is, I'd say that's pretty good.

[theholycow]

The best thing you can do is fix that speedometer/odometer or start using a GPS to keep track of distance so that you can measure and track your fuel economy. Only once you know and track your fuel economy can you begin to improve it.

[sk6strng]

Thanks thisholycow...My wife wants the speedo to work also.....I personally like being in the dark....'specially about my mpg's

[theholycow]