I'm getting about 12-13 mpg, with a pretty much stock 283 with a 500cfm 4bbl, 3:55 gears 32 " tall tires. Would a 2 bbl help with this?
kind of depends if you drive around with the secondaries on the carb open? (like, your foot is always to the floor) If not, then going to a 2bbl won't help.
Everything is good. Low mileage rebuild, new carb, distributor, spark plugs, timing is good. It has double hump heads. Runs great but gas mileage is crap, and I don't drive it hard. This is on the highway too.
3.55 gears are probably a factor. Unless you drive like I did when I was 17, the front half of a 500 cfm 4 bbl should get better mileage than a 2 bbl would.
With the 32 inch tall tire, 3.55 Rear and a 1 to 1 high gear at the output in the trans you should be turning 2609 rpm at 70. A 70% overdrive would drop that down to 1830 Still total state of tune and driving habits have a lot to do with gas mileage. Even tire pressure especially if you 32 inch tall tires are 8 ply or more light truck tires and you are running low pressure to soften the ride.
If this is your highway MPG what is your city? Same or different? What is your average speed on the highway? How are you calculating the MPG?
I had a 265 with a cast iron powerglide in a 56 9 passenger wagon that got 14-16 in town and 18-19 on the highway with 3.36 gears. Rochester 4Gc carb. My 35 has a 350/200 4R tranny and a 3.55 gear. 600 Edelbrock carb. It gets 18 consistently. Just for reference.
I can get 2 mpg - 3 mpg better mileage then my wife can get from the same car, on the same day, on the same drive, at the same distance. Driver style has a lot to do with gas mileage. Traffic flow has a big effect on driving as does the speed, the road surface, and the terrain your driving around in. The 318 in my truck gets 10-12 mpg right now. Its suppose to snow tomorrow, in 4x4 around town it might get 8 mpg, but next summer it will get 15 around town and near 20 on the highway. Shouldn't I be getting better mileage? Based on last summers numbers, yes, but it isn't summer, the gas isn't formulated the same as it was last summer, and the truck isn't getting used the same way it was then. Install a vacuum gauge attached to manifold vacuum, and drive it without the vacuum reading dropping below 14, then tell us the mileage.
big question is, what does it run in the 1/4 mile? If that number is respectable, who cares what the mpg number is....
What transmission are you running? I've always found those cast iron Powerglides to be a power robbing piece of crap. I had a '55 Chevy with a fresh 265 and powerglide. It was working fine except it didn't have the power I expected to get up long steep hills. I bought a '57 wagon for 150 bucks to get the 3 speed stick conversion parts. After setting that up it would go up the same hills easily and gain speed doing it. Gas mileage improved, too. I don't like 'em and never did. Thus sayeth the old grouch.
Bought from a friend, whom I trust he told me a known engine builder in the Twin Cities rebuilt it. When I got it home I pulled the heads, the cross hatch was like new. 350 trans. 500 cfm Edelbrock carb. About the only time it sees in town driving is to get to the highway. I think I'll have a local guy tune it to see if that's the problem.
sounds to me like incorrect calibration on the carb. you need to tune it with jets and metering rods. I think all of those carbs come new with calibrations like it is going on a 350
That’s probably about what it got when it was new. I have a 350 lockup in mine and it gets about the same. Mine it 4:10s with 35 inch tires.
When I had a 327 365 in my 30 A 29 tire 3:42 gear 1:1 350 trains 2,200 converter 16-18 mpg, 100 miles half stop & go ,& hyw 427 over 650hp normal drive 14ish mpg 427 on same drive with 4 pulls in 1/8 , 10mpg
The 32" tall tires reduce the gear a bit. I have a 31" tall tire on the rear of my truck with a 3.42, turbo 400, and a Buick 455 in a 3,300 lb truck and I'm getting better mileage than this guy is even though I recently had an exhaust valve hanging open . Scoop, I'd be willing to bet that your timing and carb tune are off. Have you run a compression test? Do you have a valve hanging open or anything? A well-tuned fairly stock SBC should get better mileage than that in a light car with a 32" tall rear tire. Something is amiss.
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