I took my ’76 Trans Am out yesterday; I needed a reboot – and it needed exercise. Drove the orange-painted, screaming chickened “gas guzzler” around for about an hour, taking my usual route out and back. Full tank when I left. When I got done, I refilled at my local Marathon. I used about 4 gallons to travel about 60 miles, so about 15 miles per gallon given the car’s 21 gallon fuel capacity.
The 2021 Hyundai Veloster N press car I’ve been driving around all week (reviewed here) averaged 24.3 MPG, according to its computer.
Forty-five years is a long time. But it’s not that much of a difference – particularly when one takes into account everything that has changed over the 45 years that separate a car like my old “gas guzzler” from a new car like the Veloster.
My Trans-Am’s V8 has twice as many cylinders as the Veloster’s four cylinder engine – and is nearly four times the displacement (7.5 liters vs. 2.0 liters).
The Trans-Am’s V8 has a big four barrel carburetor that literally drips fuel – on purpose – into the engine, uncontrolled by any computer.
The Veloster’s engine – like almost all new engines – is fed fuel with great precision under extremely high pressure by a computer that controls four injectors, each of them screwed directly into one of the engine’s four cylinders. The fuel doesn’t drip into a warren of runners in a manifold and get sucked into the cylinders – eventually and not all of it – by negative air pressure, as is the case within my Trans-Am’s engine.
The Veloster has a state-of-the-art dual clutch automated manual transmission with eight forward speeds, three of them being overdrive gears specifically there to improve fuel economy by reducing engine operating speed at highway speeds.
My Trans-Am has been upgraded with a four speed automatic transmission with one overdrive gear.
The old Pontiac weighs about 3,800 pounds – or nearly two tons – chiefly due to the fact that its V8 is made of heavy cast iron and sits on a bolted-in steel subframe very similar to what you’d find underneath a 4×4 pick-up truck.
None of the front suspension parts are made of aluminum.
There is a cast iron rear axle out back, perched on steel leaf springs, also like a 4×4 truck’s. The hood and all of the exterior body panels are made of heavy metal – literally. Taking off the hood requires at least two strong men – and a pair of stamped steel hinges with big coil springs to support it when installed.
All four wheels are steel, too.
The Veloster – a much smaller car – weighs 2,987 pounds, almost 1,000 pounds less. As it should, given its engine is a fourth the physical size and made of aluminum; given it hasn’t got a rear axle at all (being front-wheel-drive) and given that many of its suspension components are also made of aluminum – as are all four of its ultra-lightweight wheels.
It does not have a bolted-on subframe. It has an integrated unibody specifically designed to eliminate the weight of the bolted-on subframe that used to be commonplace in cars (at least, American cars). Its hood is so thin and light a man – just one – could literally bend it with his bare hands. It is so light that all that’s needed to support its weight is a pencil-thin prop rod – as is commonplace in almost all new cars.
The point here is that in spite of all of these advantages – much lighter weight, much less engine and much more in the way of technology, including an engine management system that micromanages fuel/spark and every other parameter to maximize the MPGs – the 45-years-newer car only manages to deliver about 10 miles-per-gallon better than a literal antique car without any of those advantages.
It makes one wonder what a car such as the Trans-Am might be capable of if it had some of those advantages – and not even all the way. For example, a basic fuel injection system such as those that can be easily retrofitted to old cars like mine. Not direct injection like the Veloster’s – which is a hugely complex system that would require redesigning the old Pontiac’s engine in order to install it. Just a simple, bolt-on throttle body-type system.
The MPG difference would likely decrease to about 8 miles-per-gallon and maybe even less.
Which makes one wonder why new cars like the Veloster use so much gas – relative to the gas used by old gas guzzlers like my Trans-Am.
The answer isn’t mysterious. It’s physics.
My Trans-Am’s engine makes horsepower the old-fashioned way, via displacement. Originally, it made just 200 horsepower. I made some upgrades – a performance camshaft being the major difference – that increased its output to around 275 and perhaps even 300 horsepower, which just happens to be about the same as the Veloster N’s 2.0 liter turbocharged engine makes.
In order for a small engine like the Veloster’s to make the power of a big engine, its effective displacement must be made comparable to that of a physically larger-displacement engine. My Trans-Am’s big-displacement V8 can draw in a lot of air – and there is a lot of room inside its coffee-can-sized cylinders. The Veloster’s little four is force-fed air, which is stuffed into its much smaller cylinders via the pressure of 20-something pounds of turbocharged boost.
This makes them bigger – or rather, it enables them to take in more air (and fuel).
No matter how you make your horsepower, in other words, it takes the same energy (fuel and air) to make it.
Hypothetically, the turbocharged little engine can deliver more than a 10 MPG difference vs. a much bigger engine like my Trans-Am’s engine, which is always a big-displacement engine.
The Veloster can get as much as 33 or so MPGs on the highway – provided it’s not on boost. But that requires a light foot. As soon as you dial up the boost, down go the MPGs. Which means the mileage potential is more hypothetical than actual. The Trans-Am’s guzzling is more honest in this respect.
It is also more relaxed.
That big engine doesn’t have to work as hard to make horsepower and it is without question under a lot less pressure – literally. Its pistons, connecting rods, bearings and so on aren’t being stressed nearly as much – and not just because they aren’t under as much pressure. The smaller engine’s smaller parts have less material – including surface area – to absorb all of the stress imparted by all that boost.
My Trans-Am’s engine has had one rebuild in 45 years. How will these heavily turbocharged engines fare over the next 45 years?
One wonders whether any real gains have been made.
. . .
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