Here is the engine in the Duster that I'm building for a series in Car Craft. This engine makes 700 hp on the dyno but it should run down the road just fine. The idle might be a little aggressive since I don't have variable cam timing but it won't be bad. It will idle better than 90% of the hot rods out there that have a carb and it will get better fuel economy. Very, very few guys know how to tune an engine better than the feedback loop on an EFI computer.

It will get about 4 mpg. DOUBLE what I get in my Dart with a 4150. The old cars were great because they were topped off daily with cheap primo before going home from work. The gas stations were always full of bull, especially when you drove in to the isle, driving a striped, muscle car with high impact paint. At night, under the lights, was even cooler. Stopping for a cold beverage wasn't unheard of. So my take on this is that if you are going to daily drive an old car, with any "performance" mods at all, get ready to pay the piper. Even the newer, high powered cars burn GAS! Big time! You might get 20 idling down the road in overdrive in a new Corvette. Only because I think it would be the lightest of the bunch. I know nothing about foreign cars and their engines.

This thread and its posts touches on another important question:

How much are EPA regulations on automobiles alone actually costing the typical citizen?

How much $ would be saved by the typical citizen if their vehicle's engine was optimized for fuel economy?

Another related question:

How much UP
would NOx, CO, and HC go
if all engines were optimized for fuel economy?

It might be a small percentage increase like 10% to 20%
and that might be only for NOx..

Hidden things are bad for Democracy.
This is a general principle.
( there can be exceptions for Military Security)

When you buy fuel it is hidden from you how much extra you had to buy due to the EPA.

When you buy a product or service it is hidden from you how much of the price was due to the 35% Corporate Income Tax.

I think the variable valve timing, efi, variable tuned length intake runners and overdrive transmissions all help keep the modern engine near it's peak efficiency during normal driving and peak power production at full throttle. Newer engines have a less internal drag, are smaller displacement and make less power in the bottom end that our old big blocks. But the gearing and transmissions in the newer cars do a lot to keep the rpm up when you put your foot into it.

Well, efficiency is relative. Here are two heavy hitters.

My father has a 99' K2500 4x4 Suburban. Gen VI 454 BBC. It's rated at 290hp @ 4,000 RPM & 410 lb/ft @ 3,200 RPM. Vehicle weight - 5,600#. 4.10 gears with 31" tires. 4l80e transmission (4 speed).

I have my 15' Ram Power Wagon. 6.4/392 Hemi. It's rated at 410hp @ 5,600 RPM & 429 lb/ft @ 4,000 RPM. Vehicle weight - 7,000#. 4.10 gears with 35" tires. 66rfe transmission (6 speed).

BOTH of these trucks get 10mpg around town. Both get nearly identical fuel economy on the interstate. One weighs 1,400# more than the other, and makes 120 more HP and 19 lb/ft of TQ. Cylinder deactivation rarely if ever occurs, as I leave my truck in tow-haul mode. This shows how efficient newer drive lines truly are, even a watered down 392 Hemi with eagle heads (not Apache) is relatively efficient, for the most part, due to having 6-gears versus 4-gears.