I know in the last 30 years turbos and superchargers have made it easier to make power, but I always hear about huge 7 or 8 liter engines made in the 70s or earlier, that will make like 200 hp at best. How is it possible to get so little out of so much displacement?
In: 37
You might want to go a bit further back. They were using turbos and getting massive power from airplane engines in WWII
There are a few reasons, but it mainly comes down to increased efficiencies at mixing air and fuel.
Older engines had carburetors. These were mechanical devices that mixed air and fuel for the engine to burn. Carburetors were not nearly as efficient as fuel injection, which is the technology cars use today. Fuel injection gets a near-perfect air-to-fuel ratio delivered into the engine.
Older cars had pushrods for their air intake and air exhaust systems. Modern cars have overhead cams with Variable Valve Timing (VVT). The way old cars let air into their engines was completely static – now, cars can control how much air the send into the engine *and* change the amount of air sent into the engine at different engine speeds to create more efficient fuel burning.
Due to advances in manufacturing, engines now also have higher compression and can withstand higher speeds.
Finally, in regards to the 70s specifically, environmental legislation that came in at that time caused some American manufacturers to detune existing engines (made before the environmental regulations) and make them weak from the factory to meet emissions requirements, instead of designing new engines right away.
The science of building engines has advanced significantly. Engines are mass produced at nigh higher tolerances these day. If an engineer wants a hole with a diameter of 4 inches today you get a hole with a diameter of 4 inches +/- a few thousandths of an inch. This means pistons of the cheapest mass produced engines today seal up much tighter than those built 40 years ago leading to less exhaust gasses escaping the combustion chamber that reduces efficiency. These tighter tolerances also allow you to run lower viscosity oil which is easier to pump.
Cars are now all fuel injected instead of carburated which means a computer can precisely deliver the exact amount of fuel into an engine, measure how much excess fuel is in the exhaust, how much air is going through the intake and make adjustments depending on throttle position and engine load. Engines also can make adjustments to advance or retard timing of the spark do adjust and when the intake and exhaust valves open in relation to each other. While at low RPMs the air flows slowly through your engine which doesn’t promote swirling of the air fuel mixture leading to a less efficient burn. Modern engines can open the intake valve later or open them less to speed up the movement of the air then at higher RPMs it will gradually open the intake valve more and earlier when the air flowing through it is moving faster. The same principle applies to the exhaust side to harness the inertia of the exhaust gasses flowing through your pipes in order to clear out more air from the cylinders through a process called scavenging. At high RPMs you can leave the exhaust valve open during part of the the intake stroke and open the intake valve earlier. This means both valves are open at the same time which allows the inertia of the exhaust gasses to help draw in fresh air through the intake valve into the cylinder allowing the cylinders to have more air and fuel in it. Early muscle cars operated in this mode all the time leading to the distinctive burbling sound at idle which was basically the engine having trouble getting enough air to keep running make it inefficient at low RPMs. Modern cars can adjust valve timing so they operate efficiently at all engine speeds.
More like 40-50 years, and a lot of this also has to do with how easy/cheap things are too manufacture. But in two words: Volumetric Efficiency. Engines are just giant air pumps. You cram more air in each cylinder per cycle, and you’ve effectively driven more air through the pump. Air moving = energy (because air has mass and thermal properties).
The higher the cylinder pressure, the more fuel & air you’ve crammed into the cylinder, the more power you make per ignition.
The biggest factor in our ability to manufacture cheap, high-pressure engines is: Metallurgy. Metals have made leaps and bounds in the past 30 years, and where once you needed expensive iron closed-deck blocks to eke out big cylinder pressure, you can now more easily do with carefully-designed, precision-machined aluminum blocks that weigh less, have better thermal properties, more homogeneous crystalline structure (stiffer), and thus can manage higher cylinder pressures (more boost).
Short answer: Better combustion efficiency, airflow, fuel control and lots more RPM.
HP = (Torque(lb/ft) * RPM)/5280
The original horse power was one horse lifting 1 pound 1 mile (5280 feet) in one minute
So a motorcycle example, BMW R1000rr ~1 liter displacement 205hp @ 13,000 rpm is over 200hp / liter naturally aspirated. The bike still makes ~83 lb/ft of torque at 13,000 rpm. Enough fuel and air into the engine though the injectors. Then the correct compression, ignition and power stroke. Then the whole motor is designed to be optimal for this power.
Nothing off of a race track was spinning 13,000 RPM in the 1970’s..
Incremental improvements to every individual part of the engine, accelerated by computer assisted design and physics modeling.
Also keep in mind that internal combustion engines aren’t very efficient overall at converting the energy stored in the gasoline into kinetic energy. (aka a lot of the energy from gasoline is converted into heat instead.)
My favorite recent real-world example is that a current model Ford F150 Lightning with the largest-capacity battery is only capable of carrying the energy equivalent of 4 gallons of gasoline.
The ECU.
The fuel mapping is something that just wasn’t possible to the same degree with carburetors. We can really control the combustion to create that nice even burn (I forgot the term for it, wavefront, I think) that pushes the piston down with even power.
Add variable valve timing, smart turbochargers, 4 valve designs (2 intake, 2 exhaust), direct injection (shoot the fuel directly into the combustion chamber), and you can wring a lot of power out of smaller engines. Eventually we will talk about running water injection!
2 of the 3 biggest advances in power in automotive engines today compared to those of the mid 20th century are efficiency changes. Fuel injection has gotten better, whether compared to earlier fuel injection or to carburetors. It can atomize fuel into smaller, more uniform particles and disperse them with more precision during the proper part of the cycle. Stronger, lighter materials and lubricants with less friction have become standard, losing less power to parasitic power loss, and the third thing is less efficiency related, but tighter tolerances, more precise control of fuel delivery and valve timing, and stronger materials have led to the compression ratio of a regular passenger vehicle today exceeding that of performance cars back in the previous century, while staying on the same grade of fuel.
Latest Answers