hi all, I have a '69 with a stock goodwrench 350 and I am getting horrendously bad mileage. From my calculations over the last month or so, I'm averaging about 7 mpg city and 12 mpg on the freeway. I know my mileage will never be great, but this is just pathetic. The car runs fine, idles smooth at 800 rpm and revs with no problems. My car's specs are in my signiture, any suggestions as to what could be causing this terrible fuel economy?

Have you checked the dist. vacumn advance? If it is bad there goes your power & gas mileage out the window. smile.gif

That seems real low for your set up. This may sound obvious, but are you sure your speedometer/odometer are accurate?

What are your driving habits like? What rpm are you shifting at? What speed are you driving?

Your rear gears are playing against you as well... If you have 26" tall tires and are driving 65mph on the hwy you are turing 3000 rpm. My 383 get's best mileage at 2000 - 2300 rpm. Based on that you would need to be driving between 45 - 50mph (43 @ 2000 and 54 @ 2500) to get your best mileage.

If you had 2.56's with 26" tires you would be going 58 mph @ 2000 and 73 @ 2500.

generally I drive pretty conservatively, going about 45 around town and 70 on the freeway. you are right though, at 70 I average about 3100 RPMs. My speedometer is right on, I've checked that. I also checked the vacuum advance and that is working fine as well. My friend's theory on the poor mileage is that with my higher gears and the engines tame cam, my RPMs are higher than my engine's peak efficiency, and switching to maybe a 268H might help. I was also thinking, maybe my secondaries on the carb are opening way too early.

My car's original 350 with a 350hp/327 cam in it and totally stock otherwise got right at 16.5mpg or so on the road at 70mph with my M-20, 3.31's and 25.5" tall tires.

I never checked my mileage when I had the really tall 9.50/14, Mud&Snow tires on it, but do know they made my speedo like right at 12 mph low at 70!!!

My 406 got right at 15 with it's 280/230, .480" cam and 26.5" tall tires.

I figure my 496 will probably be darn lucky to get 10!!!

I will say that the best way to increase gas mileage is to drive like you are pushing the footfeed down with an egg between it and your foot!!! pdq67

PS., and coast up hill and accel. down hill too, helps... I run my corn-popper that way all the time.

during the gas crunch days many cars came with vacuum guages that showed where your optimal fuel economy was when driving. Try to find the lowest rpm where the engine doesn lug and ping in 4th when you step on it. That should be where you get your best mpg. The egg under the gas foot thought is a good one. So many us us have lead feet!!

My old 600 with a 700r4 and 3.73s at 60mph I was doing 1900 to 2000 rpm .My gas ml was 15 mpg on the hwy and 10 in the city.I just got a 670 Avenger and I hope my mileage gets better.I was told by holley tech that the old carbs were bad on gas.I had the old 1850-3 600cfm.I'll post back after I get some miles on it.Maybe tomorrow. Good luck.Nick

Nick - Holley just sold another carb!!! I run a old 780 vac sec (List 4346) on my 383 and with a 700r4, and 3.73's at the time got 23 and 24 mpg at 60 mph. If your engine isn't making some good torque at the cruise rpm you end up dumping extra fuel through it to keep the vehicle moving... If your old carb was in real good tune I doubt you see a big difference with the new carb. If you do the old carb may actually be shot. I'll pay the postage if you want to give the old one away though!!

Dennis HI! I spend alot of money on the old 1850.I changed the floats the pump cam to green 31 shouder a 61/2 p/v the quick change v/s spring changer. That carb was hauling a$$ but the gas was something else.A body down the street was to buy the old carb!You probably right they did sell another carb!!!I don't like taking over someone elses post so I better shut-up...Nick
P/S its raining cat&dogs here today graemlins/sad.gif so no road test graemlins/waving.gif

That sounds pretty poor. With 3.73s and an M-21, I was getting between 13 and 14 MPG on the highway with my 350. That's with a signle plane and Comp Cams 274-HR.

I suspect you are running the engine out of its RPM range. Engine's are most efficient at peak torque and I bet your engine's peak torque is well below the 3,100 RPMs you are turning on the highway.