Thing about those old engines is you can tune them to do what you need. The new vehicles have a factory computerized tune that is optimized to meet some arbitrary spec, and you cannot legally change it. And since the fedgov is now going after manufacturers that maker tune kits and shops that install them, it's getting so you cannot change it; legally or not.
Back in the '80s, Hot Rod Magazine set out to prove that you actually can have both performance and fuel economy and do it in a non-aerodynamic vehicle. So they built a small block Chevy V8 with a mild performance cam, 4 barrel carb, etc. and mated it to an automatic transmission; then stuffed it in a 1938 Chevy 4-door sedan. They gave the engine a really good tune and tested it. The result? 25 mpg in normal driving, and it would run the quarter in the 13s in street trim!
Aluminum beer-can crash protection.
Bad aero. Limited interior space, etc.
Up to 400 cid can just crack 20 hwy (60-mph) in a post-1965 sedan (dual master disc brakes) with an auto. 2.7-2.9 gears (no O/D).
Highway MPG is about highest relative AVERAGE Mph to a given set speed. (Research MOBIL Fuel Economy Runs of the 1960s. Inside stories).
Spreadbore (PERFECT choke). 195F thermostat and work on ignition mech & vac advance (a lot of work). Cool fuel and hot intake (105F; except at WOT). Fuel injection is superior to a spreadbore pretty much only for cold start and altitude change.
Cam is high vacuum (not highest) and VERY fast opening (back cut valves). Total lift not impressive, it’s what happened at .050. Tight quench. (Reduction of internal friction is the more expensive aid).
Crossover behind Tri-Y headers. Chambered mufflers. 2.5” mandrel-bent aluminuzed to muffler; 1.75” to tailpipe (keep heat highest). Use Chrysler upturn before dump. Angie dumps slightly towards each other.
Tuned for throttle response.the real action is from 30-mph, or, a few MPH after auto-shift to Direct.
Part-throttle knockdown is
highly desirable. Can do a lot with that using Second
briefly to change the vacuum signal. (Better “holeshot” than T350/400 in a two-laner pass
plus used less fuel. (Rod/bell crank control of throttle & trans same advantage.
Extra Care in Engineering.
Highway cruise rpm just below peak TQ. Start with tire height & rear gears before figuring stall speed & cam/compression specifics.
As 60-Mph Is the fuel economy brick wall, that is the marker.
Not going to be a 14-sec car (fit all your family comfortably), but it won’t run out of breath on the big road. Flatten hills and pass on two-lanes with ease.
Basically, a factory car
slanted towards steady-state highway. (Worked the details to emphasize it
without losing town-driving pleasure).
MPG 30% above what most folks got back in the 1970s if serious (advantage with radial tires, gas shocks and suspension upgrades has to be foundation; rack & pinion steering would be a HUGE helpful upgrade).
Assume Auto, PDB, Posi, A/C, and some cab comfort electrics. Decent sound insulation. Try to keep TARE close to 4K. All-weather, all-day comfort is king.
Some underbody aero would be a real help.
The
OLDSMOBILE Turnpike Cruiser on the 1967 Cutlass Platform is the research model. 1970s model cars of all brands had bulk & weight gain issues.
Got my 4,800-lb ‘71 bigger Chrysler up to near 19 with above and driving skill. (Practice). Aero means more than total weight.
Never idle and never stop.
The short version would be to have
high cylinder compression. All E-Z after that. As we don’t have but cat-piss for gasoline (it’s not just octane missing) ALL ELSE is a workaround to limit pre-ignition/detonation. Early 1960s big-block Chrysler cars with only a swap to radial tires can hit high teens (all else as-new).
A turboed Slant Six would be king given the right trans gearing. Always in the sweet spot. Wind it up around town and let it loaf at cruise.
But computer-control of ignition & fuel would be the best way.
A 63-64 Newport coupe is big inside & small outside with 124” wheelbase. Of the four automakers, it had best suspension/steering/handling already in place. Best drivetrain, as well. Like all others, needs 4-whl disc.
Youngsters who think half-tons ride nice have no idea of what is “comfort”. Ease into a turn and shoot away. No lumbering about. (And you are not speed-limited as in a farm vehicle. The Letter 300 version of this car was stable at 130-mph for as long as you kept it there).
WOT up shift to Direct is at 92-mph (factory). Starts accelerating again and pulls past 110-mph. Ford 390 and Chevy 396 were gasping past 90. (
Never let a Mopar catch you, call the race early).
80% tank capacity highway fuel economy
range would be to shoot for 400-miles on 18.5/gl with a built V8-383 4V and no-slop A727. Rock-steady crisp idle. 240-HP my guess (RWHP corrected; cam partly the key and head work most of the rest); still well above 300-TQ.
V8-440 done this way is more 300/400, but it won’t break past 16-mpg. Won’t wind up as fast either. So, needs 3.23 gears and now you’re at 14-mpg most days (60-mph).
IOW, the 440 won’t matter till you’re well past legal highway cruise speed.
And that’s the game.
The A38 Dodge Polara Police Pursuit was the T-Rex of the American highway.
Nothing could outrun it . . .
except the car I’ve just described. As a savvy driver
you just have to out-last his higher fuel burn as no one is going to try a slow pass when both are already at 120-mph. (Moonshiner tactic).
In Texas DPS didn’t use the radio to call ahead. Might not be another unit for 150-miles.,
You were man enough . . or you kept your mouth shut.
When the small craft warning buoys are at the harbors entrance, the muscle car kiddies go home.
The Big Iron heads out into the night.
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