How is it possible with the Chevy’s and Caddy’s with their pure American 6 litre V8’s didn’t get past 300 horsepower.
It seems so implausible that such a massive engine was so inefficient.
In: Engineering
All in the name of fuel economy and emissions control. Big engines don’t make big power if you don’t give them lots of fuel and let them breathe well. ELI5.
Electronic fuel injection increased the efficiency or internal combustion engines by a lot. So did 50+ years of other improvements and innovations. Computerized engine control units do many things with much higher precision than the mechanical feedback systems they had back then.
Efficiency (ie hp per cylinder liters) is only one of the aspects of the problem.
By going to a bigger motor you get a more flexible motor that can handle well low rpm without the need for downshifting. That’s why these cars sometimes had only a 4 speed automatic gearbox, you don’t care about being on the right gear.
Also the quest for higher efficiency (using turbo) also degrades reliability, for example the old Volvos are uber solid because they achieve low HP compared to their motor.
Lastly, carmakers and customers didn’t care because fuel was super cheap.
In addition to better efficiency via emission controls and more precise ECMs (electronic control modules I.e. computers), modern engines are machined with incredibly tight tolerances. In other words, very, VERY small gaps between pistons and rings inside engine cylinders. Tighter spaces and smaller gaps don’t allow for the escape of expanding gasses during the combustion process result in more of the fuel/air ratio to completely do their fine tuned job. This means that there is much less energy loss.
Finally, even the engine oil used today is formulated to last longer and work harder at keeping the engine clean, lubricated, and cooler, which all reduces mechanical wear and drag. Less wear and drag = less loss of energy.
Find me a 70’s V8 and I will find you the smell unburnt petrol being dumped out the exhaust.
Modern cars are able to burn more of the fuel being sent into the cylinder before it gets pushed into the exhaust.
More fuel burned means more power for a smaller volume.
Also as others have said, tighter tolerances and better designed engine mechanisms mean that less energy is lost in friction and on parasitic drains like a badly designed fan belt or cam belt.
Computer control also helps increase the fuel burning by dynamically controlling the timing of ignition to optimise it.
You can get big power out of most of those large displacement malaise era engines, they were just “choked” due to the laws during the fuel crisis. Most of them simply need to be fed more fuel and allowed to breathe in more air and their power can be increased significantly. Changing out their cams to change when ignition happens with how much fuel at what compression also makes a big difference but sadly most of them were also built with cast heads and rods to be cheaper because they were never intended to be subjected to the kind of power their pure displacement is technically capable of producing and unless they’re upgraded to forged, they’re likely to break under high RPMs and a broken rod can be shot right through the block.
ELI5-ish, but less exactly how it is and more analogous:
Imagine you’re trying to run around your backyard while breathing through a straw because that was the only quick solution your parents (the government and carmakers) could come up with at the time to keep you from over-exerting yourself.
Eventually, your parents figured out better methods as technology progressed and you could breathe as normal.
The malaise era engines had awful compression ratios which didn’t allow them to extract all that much energy from the gas.
As a side note, the engines also were “large” in the sense of quite ample displacement, but with certain manufacturers, such as GM, the over physical size of the engine was quite small relative to their displacement.
There’s a *bunch* of factors that all make those V8s bad. The core concept of an internal combustion engine is to push old air out of the cylinder, replace it with fresh new air/fuel mixture, compress and blow it up, and use the energy from that to push the car forward. Those engines have issues at every step of the process:
– They don’t really manage to push all the air out of the engine. There’s a concept in engines known as volumetric efficiency, which is the ratio between your displacement and how much air you actually get rid of to replace with new air. For a variety of reasons, they aren’t great at this.
– Coupled with that, they aren’t able to feed more air to the engine at “high” RPMs. By around 5000 RPMs, a Chevy L58 (5.7L engine in many performance applications, also known as a 350 Small Block) will be perceived as out of breath, failing to deliver enough fuel/air mixture to the engine.
– Between the low volumetric efficiency and the fact that it gets worse at high RPMs, your 6L engine doesn’t *actually* bring a lot of fuel/air mixture in per second. A higher-revving, more efficient modern engine can move a lot more air and fuel despite being smaller – because it’s better at replacing old air and able to deliver enough air as the engine keeps revving higher.
– Once the fuel/air mixture gets into the engine, it needs to actually be combusted. We have gotten a lot better at this, and old engines were just not as good at combusting all the fuel and getting it to release energy. Fuel injection and modern engine control units are largely there to make it combust *really* well, and these engines have neither.
– Then, we need to actually turn all this heat into useful work – but there’s a bunch of things stopping us. Most notably, there’s friction in the way – friction in the valvetrain, friction between the pistons and the cylinder walls, friction on the way down to the crankshaft and so on. That friction steals power from us, and we have gotten better at reducing it.
TLDR: Newer engines bring more fuel and air into the cylinders, get that fuel to release more energy when it’s ignited and lose less energy to friction.
To add onto a lot of the other comments here about efficiency, ECMs, etc, the big difference was the oil crisis of the 70s combined with the emissions regulations implemented since 1975 (put into place in 1970.
ELI5: We make gasoline from oil, and during the 1970s the prices of oil not only started to go up a lot but also became more and more unreliable, leading to people even waiting in line just to put gas in their cars, or only being able to get some on certain days. The U.S. also put into place a plan to help stop the pollution from cars, especially because they were still using gasoline with lead in it. Part of how those emissions laws would work was making manufacturers install catalytic converters onto cars, which did not work with leaded gasoline. At the same time, Americans were beginning to look for cars that got better mileage because of how expensive it was getting.
Car manufacturers knew that they had to do what these laws said, but also they had all these engines sitting around, and the tools to make them, and decided to just put the new emissions required catalytic converters onto the same engines that they were using before, and also making them run on unleaded gasoline, both of which reduce the power output of an engine and system designed to not use those. This meant the engine couldn’t breathe as well, didn’t make as much power from the fuel, and it would be a long time for the big American car manufacturers to design new engines and systems that were following the new laws, and that would get better mileage. From there the engines got smaller and more efficient (for the most part).
Little addition maybe outside ELI5:
“For one thing, there’s the issue of the actual rating process. Before 1971, engines were factory rated using a process defined by the Society of Automotive Engineers as ‘Gross’ horsepower. This figure was calculated on a test stand with no intake, exhaust or power-robbing accessories attached. After 1971, power levels dropped as manufacturers re-rated engines using the SAE’s ‘Net’ process, which added intake and exhaust restrictions and the load of engine accessories, like the alternator and power-steering pump. ” [Source](https://www.autoblog.com/2013/08/15/modern-vs-vintage-horsepower-through-the-years/)
Not answering the “why” of this question but just some more context I always found interesting when people talk about the big numbers.
Am I the only one who thought OP was talking about the drink V8? It’s too early for me 😔
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