kansas123

I am somewhat disappointed in the gas mileage I am getting. Not looking for 25 mpg, but would love to get 15, in my '72 350 Automatic. And I don't drive it hard at all, just cruising. Newly rebuilt distributor, new plugs and wires, and timing. It could be idling a bit fast, will know in a few days when the tach is reconnected. I am ordering a rebuild kit for the Q-Jet, after that I am at a loss. I am guessing the rear end could be influencing the mileage but don't wanna change that really. Probably the 3 speed also? Did they have 4 speed automatics back then?

400hp427vette

advanced timing or the carb running rich could be the cause of this.

Glass Act

Our 72 with a 350ci stock 200hp / 4speed / 3.36.1 stock rear gears gets about 18 mpg.

Our 79, far from stock 400hp / auto / 4.56.1 rear gear gets about 10 mpg on a good day

And no there is no 4 speed automatic trans.

kansas123

Wow, there's hope after all...........thanks for the glimmer....

RIJVETTES

Finish the Q Jet rebuild and recheck your milage. Accellerate like there's an egg under the throttle- but that will eliminate the fun. The addition of a 200 4R or 700R4 trans will definitely improve your milage- thats why GM did it in 82, and its my next major improvement. I expect about 19 MPG with a rebuilt 355.

Five-spot

What are you running for plugs? Better plugs tend to run more efficiently and improve your milege at least some.

rihwoods

I got 14.7 running 70-75 mph Sunday...212 miles...78 L82 4 speed 3.70 gears...

SuprJames

Time for a 700R4. You will enjoy your cruising much more

enkeivette

OD is great. I get less than 10 in the city with easily over 500hp, but more than 20 on the highway.

Ron R

Hold up guys, you really need to do some math here before recommending a tranny swap.

First, what are you going to pick up MPG wise by changing to a 700 R4 ... 5 MPG? Maybe six? Think this through, because what you're basically about to do is drop a couple grand (figure $1,100+ for a rebuilt tranny, then you need the drive shaft, tach gear, and if you can't do it yourself you gotta pay someone to do it for you.

Check the formula - upgrades typically cost more money than you'll save on gas.

http://forums.corvetteforum.com/show...post1565027431

GrandSportC3

If you are looking for fuel efficiency, I'd recommend a edelbrock carb and a 200R4 transmission.. I bet that you can get close to 20 mpg on the highway.. I used to have a 383 with 465 HP with a Holley HP 750 carb and a Tremec TKO 5-speed and got about 17 - 18 mpg on the highway..

TedH

With my '80 L48 tuned for performance (timing advanced), I get about 15mpg with my 700R4 and 3.54 spicer gears. I suspect I could get 18mpg... but I'd have to back out my agressive recurve and retard the timing... not gonna happen. It's not driven daily so I prefer the spirited performance.

Backstop

True, but you could recoup some of that in resale value. A few years down the road when gas is $10 a gallon and there's a guzzler tax that mod will look very nice.

Ron R

Here ya go, I put the formula up on a web page:

http://www.corvettelink.com/fuel_savings_calculator.asp

pbcanney

somethings going flookey with my pc today.

I SEE the Corvette at the top but I swear I'm trapped in the Prius-Hippie-Forum

Greg73convertible

If it's a daily driver do a 700r swap I had one in my 76 and it was great (lower first gear too !!!!! ) can't wait to see how my 73 does with tpi and 700r I think Im 2 mos away

kansas123

Running AC Delco R44T, this is stock for engine and year.....

tigers123

Mine has a stock 350 with headers, aluminum intake weiand 8004,edelbrock 650, th400 headers, and flow through exhaust and will get an honest 18 mpg on trips. Maybe that will help.

milo30

I would guess that your biggest killer on your car is your gears. Change those for mileage and you'll lose the performance feel. I don't think I ever got more than 14 MPG tops.

Is it a daily driver? I threw some numbers into the calculator that Ron posted. It looks like around 24,000 miles to break even. Bump the price up .63 cents and it drops to around 20,000 miles. The better price that could be found on a used tranny would help in the savings.

I don't know how to calculate the wear and tear on the engine. I have 3:70 gears and my RPMs seem to be way up there. I'm sure that using an OD would increase the life of the engine which would also save $$$ a few years down the road.

For a DD, I think that you could justify the cost. I'll put over 20k miles on my car in 2 or 3 years. I live in a state that enables me to use the car year round. A weekender car only, then it doesn't make much sense for mileage only.

enkeivette

5-6 mpg, that's a lot! Junkyard 5 speed for a couple hundred, fab whatever you need to make it work yourself. I did for my 6 speed (without a welder). Cut your existing driveshaft. Boom.