SLANT 6 a GAS GUZZLER?
I have a 69 Barracuda convertible with a slant 6 and the following setup:
Compression is ~9.0:1 (I'd have to go look at my data book for exact)
TRW stock replacement cam (Again, data book for year application p/n)
OD 4 speed, aluminum case
2-1/4 exhaust - entire headpipe to muffler
Reproduction 340 A body muffler (a bit noisy)
Holley Economaster 1920 carburetor
Stock Aluminum 1 bbl intake
7-1/4 rear with 2.76 ratio and rebuilt, plate type sure grip
215/60-15 tires on stock steel 15 X 6.5 wheels; 4.5" bolt pattern
Chrysler Electronic ignition
Distributor recurved to provide 30 BTC max mechanical with 10 deg initial
Standard Ignition p/n VC 208 vacuum advance canister (lots of vac adv.; 24 max)
SPAL electric fans (necessary due to aftermarket A/C)
I just took a trip to Oregon from L.A. and got a best mileage of 29.4 mpg on highway 5.
Speedometer is dead on based on matches to radar speed warning signs, at speeds between 25 and 65 mph, at 6 different locations around L.A. and Santa Monica. Odometer not tested.
Driving along the coast on windy paved and dirt roads, and constantly varying speeds between 25 and 55 mph, I got a worst of 23.4 mpg. And that was with the top down.
Combined around town going to work each day, I average between 23 and 24 mpg. I haven't yet gotten below 23 since the last distributor recurve step. As a side note, I started with an NOS 1976 slant 6 distributor and only got about 18 mpg using it out of the box with the stock advance springs and vacuum canister.
All pieces are important, but the two keys are probably the distributor recurve and the OD 4 speed. I had a 68 fastback Barracuda, 318 w/360 heads, Thermoquad, and cam in between stock 318 and stock 340. Standard 4 speed, car got 19 mpg highway best. With only a change to an OD 4, mileage went to 25 mpg highway.
Hope this helps you.
Bob