My 67 is getting about 10 mpg, its running with a 327(350 horse) mid cam 650 edelbrock , 700R4 trans (2200 stall)12 bolt posi 331 gears. I believe that I should be getting closer to 20mpg, can't seem to find the problem. Any help would be appreciated.

Thanks,
Ken

uummm...keep your foot out of it, lol.

the 350 cam isnt really a mild cam in a 327 btw.
check for dragging brakes.
or put a two barrel carb on to save gas

Tuning. Ignition advance curve. Carb jetting. There is a lot more there.

What do your plugs look like? Black I'll bet.

btw just bustin your nuts:D

With the new tranny and the rear gears are you sure your speedo is correct?

What method are you using to determine your MPG?

To All, plugs look good, timing is correct for engine, car runs like a top, brakes not dragging, and keeping my foot out of it. method of checking mpg; gallons used for actual miles drove. have correction for speedo, tire size and all.
Car has hedders and HEI system, plus nice sounding flowmasters,traction bars and old style cragers (15 in)
So, looks great, runs great has bad mpg, any other suggestions?

Thanks again,
Ken

alignment?
also smell your oil my buddy noticed a pronounce increase in fuel usage and found out the oil smelled like gas .
found out the rings were going.
car had blowby too.

Tire air pressure?
Extra weight not needed, in the trunk?
Front/whole car wheel alignment?
Front wheel bearing preload?
Slippage from high stall convertor?

As said, 350 HP cam is big in a 327.
Idle vacuum reading is ___?
Cruise vacuum reading is ___?

Have you had someone follow you in another car and track speed with 2way radios? You could be driving 40mph and really are going 50mph and that will mess up the mileage figures alot.

Assuming your speedo is callibrated I don't think 10mpg is what you should be getting unless you are talking about city driving not highway. I feel too many guys put together mis-matched combos and because they use an OD trans, high gears and a small carb they expect it to give them great fuel economy.

To utilize efficently the high gear (OD and rear gear ratio) your engine needs to make torque at the rpm you are cruising at. A 327 is not typically making a lot of torque below 2000 - 2500 rpm. If you are cruising @ 65 mph and taching 1500 rpm (just an example) you will be dumping the fuel in to keep your 3400lb car moving.

Something you can try is to make say a 100 mile hwy run at 65mph in OD and check your mileage. Then make the return trip at 65mph but leave it in drive (1:1) and compare your results. My money says you'll see better fuel mileage without the OD. If this proves out I'd suggest a 3.73:1 rear gear to get your rpm up a bit in OD.

To All, I will try all suggestions and get back when finished.

Thanks,
Ken

15" wheels! how wide are they? tire size? are they steel or aluminum?

Using vac advance? Lean your carb out till you get a stumble, the richen a touch to clear it up.

Still working on the problem, speedo is now corrected, tires/wheels are cragars (steel) 15x7, front bearings are good, wheel alignment is correct, no drag on brakes, car is running about 2100 rpm at 65mph, no gas smell in oil or anywhere, vac advance is working. I still have to make a long run with it, last tank of gas/milage was 10.55mpg. Still along ways to go. I will be checking out the carb this week and all vac lines again.
Anymore suggestions?

Thanks for all the help,
Ken

You might try a front set of 14X5 steelies for giggles. Fifteen by seven's have a shallow backspace placing the tire centerline beyond/outboard the intersection of an imaginery line through the ball joints and tire centerline at the road surface.

As an example, turn the front tires sitting still, then raise the front tire and check the rub spot on the tread. It should be in the middle of the tread.

Any part of the tire beyond/outboard the intersection of the imaginery line through the ball joints and the road surface makes for a longer lever on the tie rods and folds the wheels towards the rear axle and the tires scrub the road surface. Your alignment for toe-in is static, not dynamic.

More air in the tires?

Another factor would be your engine set-up; 350 HP 327. This is radial set-up for the street. Your operating rpm is below the designed rpm for the camshaft. Operating at a low rpm, OD plus 3.31:1, places the fuel coming from the idle transfer slots and not the main circuits.

Run the car in Drive and calculate the mpg. Might get better even with the high stall convertor. Might even put full manifold vacuum onto the vacuum advance cannister. Doesn't hurt to experiment.

The above suggestions are just my thoughts, except for the 15X7's to 14X5's I had a Dodge truck, came OE with 15X6 rims. I installed a set of 15X7 Keystone Klassics and lost 1.5 mpg in-town. Swapped 15X6 steelies and gained back mpg.

Hi Ken
i was only getting 10 mpg from my 307,till i found fuel leaking from the gaskets under the primary boosters . I run a carter AFB which is similar to your Edelbrock ,it now does 13mpg around town and 16/17 on a run.Iam sure you,ve checked every thing is tight , its just a problem i came across.
Pete.

i have a mild 350 with 270 cam 355 rears,15x12 tires,turbo 400 2500 stall .i only get 11mpg .im running a holley 650dp.

What part of Calif are you in?

Unless you have installed an O2 sensor (wideband preferred) in your exhaust or paid someone to tune it on a dyno (with an O2 sensor and or a 4-gas analyzer) and tuned your carb jets/metering rods then you havent "jetted" your carb to optimize mileage.

Tuning the dist advance curve and vac. adv. diaphram involves an advance timing light at the least so you can check when and how much advance is coming in on the dist. Vacume advance will have a dramatic effect on mileage. You cannot simply set your base timing to "spec" and assume the advance curve in the dist is accurate or functioning or that the vacume advance is tuned correctly either.

Installing a vacume guage and monitoring it while you drive will help you get it close and gives you an idea as to what kind of load the motor is under. (Higher vacume means less load, better efficiency, lower vacume means higher load/worse economy)

Chris:cool:

Am i wrong in thinking that switching to a 2 barrol carb would worsen his gas milage? I always thought that a 2 barrel had 2 bigger barrels than the first 2 on a four barrel. So as long as you kept the secondaries closed (Kept your foot out of it) then a four barrel was better on MPG.
Have i been wrong all these years thinking that?

Tom, if your thinking is wrong, so's mine.
And speaking of gas mileage, 34 years and counting. Yep, never checked the L88. That's not what it's for!:D

.......And speaking of gas mileage, 34 years and counting. Yep, never checked the L88. That's not what it's for!:D Exactly, my wife mentions something about it a while back and i told her if i was worried about gas milage i would have bought a toyota.