Improve gas mileage on a 427 so ?

[MKS427]

Short of tearing it out and using for a coffee table, it's going to use generous amounts of fuel (about 740 cfm air/fuel @ 6000 rpm). The only things that come to mind are a smaller cam and possibly an EFI. The cam will impact power and the EFI benefits depend on how well your carb is working. Running the engine lean is not recommended, so there are limits to what you can actually save.
I'd recommend evaluating initial cost vs long term savings vs fun factor sacrificed vs how much you drive. The price of fuel may be the least bitter pill.
Good luck,
Mark

[Dwight]

Ok I'm going to give you the short story

A few years back I installed a dyno-ed 530 hp 408 in a Cobra for Mike. He drove it 130 miles home and called me about the gas mileage. 6.7 MPG.
I told him to bring it back and I would let Coach tune the carb.
We called the shop that had build the motor and they told us they only tune for wide open throttle because they did not know what air filter, alternator, headers, exhausts system, etc that we would use.
Mike brought the car back and Coach tuned the carb. Trip back home he got about 13 mpg.
The next year I drove it to the London Cobra Show. Round trip 1150 miles and I got 16.7 or 17. something, don't remember for sure.
Moral of the story is check the power valve and get the carb. tuned. There is more to tuning than adjusting the idle screw. Jet size, air fuel ratio, cam plays a big part.
Air Filter is a big issue on fuel consumption.
I had a 351 W one time that would not rev over 4300 rpms in any gear. Stopped on the side of the road and removed the 8" air filter and the motor would rev to 6,000 in any gear.
I'm with Eric on this gas mileage thing. If I can change something to get another mile out of a gallon of gas, I'll do it.

[1795]

In addition to the above mentioned things, take look at the differential and go with something in the 3:54, 3:31 to3:27 range.

If you keep the rpms down you will get better gas milage. A 427 running at around 2,000 rpms will have more than enough power move a cobra. Do not run the car at 5-6,000 rpms, no real need to on the road.