Submitted by Micromashington t3_yhxodk in explainlikeimfive
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?
Damn you just answer everything lol. Thank you.
...and computers. That fuel/air ratio does not mix itself!
There few thing which should be adressed too
Better lubricating oils and steel quality allows engines to opperate on higher power without melting.
Better design of valves. Old valves had ton of space between them and engine walls. Thus lot of conbastion agent were escape prior burning, greatly reducing power. Big distance was important for 2 things. First manufacturing was on much lower level and offset could be big. Second steel quality resulted in high expansion of metal, so it was important to leave space to prevent stacking and wall break
I think your statement about push rods vs overhead cams, while mostly accurate isn't completely true. Push rod engines were still used by a lot of American manufacturers throughout the 1990s and I'm pretty sure Ford still has engines using push rods. I do believe Ford was able to get variable valve lift with their modern pushrod engine but I'm not totally sure on that.
A lot of (mainly American) manufacturers maintain that pushrod can be superior due to lower centre of gravity. i.e. the main cam is deep inside the engine.
It's also simpler and weighs less, especially a V8 with double overhead setup. The four cylinder overhead cam isn't as bad cause you just have two instead of any V config will have 4 cam shafts. Weight can effect fuel economy and simple (pushrods) always has its own benefits.
The GM LS-family of engines is exceptional, and they use pushrods. It was an attempt to see how much modern design could keep pushrods relevant, and the results were good enough to continue pushrods for quite a while.
The main benefit is they cost less than OHC, especially if you are only using 2-valves per cylinder. They also allow a shorter engine, but that's only a benefit for something like a Corvette, while millions of SUV's from GM didn't care if a pushrod engine was an inch shorter.
I would go so far as to say that if you are adding a turbo or a supercharger, you only need 2-valves per cylinder. For naturally aspirated, OHC and four valves per cylinder seem to be dominant, so there must be a benefit to that.
I think the most significant is higher RPM. pushrod engines have a tendency to fly apart at higher RPMs, whereas DOHC do not.
not at all true. the 289 in my 65 mercury would hit 9k no problem. and that car was from 1965. the biggest problem at that rpm is valve float. the biggest benefit ohc engines is better variable valve timing. its easier to independently control intake and exhaust timing with ohc engines. and it couldve been done with no cam if freevalve had taken off earlier. that couldve pushed ICE engines another decade if they got it out the door sooner.
What variety of that engine did you have? Since I read the stock Ford 289 redlines at 5500.
Is valve float the fact that the valves can't close fast enough?
To add to this, before the advent of computer chips, we could not adjust timing "on the fly" to avoid detonation (gasoline igniting before the spark event).
For instance, the GM LS engine family has an "anti-knock" sensor that can detect the beginnings of detonation before its audible to the human ear, and it will then retard the spark to allow the cylinder in question to cool down a hair.
Before that technology, the compression ratio had to be chosen to work for all engines across the entire country, using all grades of fuel, even fuel with variable quality from a low-quality brand.
Now, the LS family of engines can come from the factory with a relatively high compression ratio.
In the early 1970's, lowering the compression ratio a bit was the fastest and cheapest way to lower cylinder temperatures, and thus create less emissions of the type that was being measured.
Thanks, BlowjobPete!
Don't forget that the methods of measuring power are questionable at best... Even today.
Can take a car from ford, bmw, vw, Mercedes, and dodge and toss them on the same Dyno on the same day and there is a decent amount of variance between their self reported and actual...
Most notable the BMW 335 from the mid 2010s where it somehow was developing more power than claimed.
Where most usually develop 10-20% less due to drivetrain loses
Transmissions that have upwards of eight forward gears also help efficiency by keeping the engine in its most efficient rpm range longer.
There is so much wrong to this and miss information. First Carburetors make MORE power than fuel injection. Seems wrong but it’s not, that’s why a lot of your big power stuff uses them. Fuel injection is preferred because it doesn’t have to be adjusted as it adjusts itself and can give better fuel mileage. It’s much more convenient, but if youre looking for max power? Carbs are still king.
Not all cars run overhead cams and many of your big power vehicles dont. Look at your supercharged LS’s in your C7 ZR1 or your Dodge Demon with its Supercharged V8, bother run a single cam in the middle and make more power than people know what to do with. Having multiple overhead cams isn’t a necessity and it’s generally not even a major advantage. VVT doesn’t help for Max power and many vehicles with a single mid block cam still have it. VVT allows vehicles to adjust their cam profile to give more low end power. So rather than have a cam that makes big power from 4,000-6,500rpms they can adjust the valve timing to extend that range from 2,500-6,500 without losing maximum power.
Compression is something we’ve always had (and compression was actually pretty high in the past) and how fast an engine can spin has little to do with anything as they don’t really spin engines much faster than previously.
It all boils down to your last paragraph which is like half right honestly. So I’ll give the actual explanation down below.
Cars from the 60’s and 70’s weren’t low on power. In 1968 Chevy released the Corvette ZR1 with an L88 engine that made over 550 horsepower with 610ftlb of torque and 12.5:1 compression. A fucking monster even by today’s standards. So no power and compression was certainly not the problem. Now not all of the engines of that time were so powerful most of them were in the 300-400hp range (for performance engines) but that’s not the full story. They had lower horsepower but much more torque. Back then it was about having that low end grunt that got you moving (torque) much rather than horsepower which is what’s helpful going 150+mph. They had different goals and we don’t see vehicles today naturally aspirated that come anywhere close to those levels of torque.
So what happened? Why did we see the power levels fall from the muscle car era? The first thing people point to is emissions, and sure that played a huge part. Smog was at record levels in the 70’s and they needed to bring it down, so they cracked down on emissions. Naturally emissions control makes vehicles have less power. There was also a second aspect which isn’t as often talked about, and that’s the gasoline. Back then they ran leaded gasoline which is not a thing anymore. Lead in gasoline raises the octane by a LOT. You can still get it but it’s for off road use only because of the health risks. The thing though is cars now have to survive on unleaded 91 octane instead of like back then when it had lead in it and was basically race gas. If you modify a vehicle today (especially a turbo car) to accept leaded gasoline, you can see improvements of a hundred horsepower easily on a stock vehicle. In my race car I get 600+ horsepower switching from 91 to C16 (116 octane leaded fuel).
Between those 2 things that how we ended up with vehicles like the Mustang that went from a 428 cubic inch cobra jet engine making insane amounts of power to a 4 cylinder in the 80’s. The one thing that came out of this was vehicle weight, in order to reduce emissions cars became lighter which was the muscle cars of the 60’s and 70’s biggest downfall. Lighter cars are faster. In addition to that after a lot of technology manufacturers have increased the flow rate of cylinder heads which give more air for more power. Look at a set of stock LS3 cylinder heads and they will outflow modified big block heads right out of the box. On top of that it’s cam profiles, balancing, and finding ways to increase compression back to the glory days without detonation due to the lower quality fuel. Still to this day though those old engine designs from the 60’s mixed with the learnings over the years are still the most powerful engines. A modern engine can’t even come close to the power output of a old big block Chevy when modified.
So in short fuel quality and emissions is the downfall of engine power, and engines didn’t have as high of horsepower in the old days because they were designed to give more torque. At the end of the day the old saying still runs true which is “there is no replacement for displacement”. The bigger the engine the more power it can make. Power adders like super chargers and turbos just add artificial displacement. Vehicle manufacturers today strive for high horsepower rather than torque which is why it seems like they make more power, but in reality they don’t. Look at the Honda S2000 for an example 237 horsepower seems nice but only 162 torque compared to that L88 which made 550+ horsepower and 600+ torque. It’s all in what they are building the engine to do. The only thing they have accomplished really is making engines more fuel efficient and not use leaded gasoline.
This is a sort of minor point, but just to make it clear what you're saying, it might help to define what you mean by power. At the end of your comment you draw a distinction between horsepower and power, so I'm assuming that when you say power, you're not using "power" in the physics sense of the word (amount of work done per unit of time, measured in Watts), since HP is a unit of power (one HP = around 750 Watts). I think, from the body of your comment, that by "power" you mean torque at low RPM, or maybe the minimum amount of torque available across the entire RPM range.
I'm not trying to disagree with anything you're saying (I'm nowhere near knowledgeable enough), just pointing out that the terminology used by people with automotive expertise may differ from the terminology commonly used in other areas (sciences, some fields of engineering) in a way that causes some confusion.
I'm also curious, what would you say is the reason why cars with lots of low-RPM torque were so popular? How much do factors like being able to produce very high HP or large amounts of torque actually affect people who just drive their cars to work / the grocery store?
So power was used intentionally because of the point I’m making as it’s a broad term referring to the capabilities of an engine. Realistically the only thing we measure on a vehicle to determine it’s “power” levels is torque. Torque is the amount force the engine produces. Horsepower isn’t a thing measured but a formula. Horsepower=Torque*RPM/5252. So when I say “power” Im referring to the amount of force an engine can put out without a specific measurement.
Why were cars back then so interested in low end torque has multiple reasons. The first reason is because it’s just a matter of design. The bigger the engine the higher the inherent torque. If you look at naturally aspirated engines there is a typical trend that larger engines have bigger more torque. It’s just physics at that point.
The other reason is because it’s more enjoyable to drive. There’s not a lot of places you can go to crack open that horsepower and push the car up to 150+mph. By prioritizing low end torque you get that super quick acceleration while not having to push the vehicle to unsafe speeds.
Incremental improvements to every individual part of the engine, accelerated by computer assisted design and physics modeling.
Also, metallurgy has improved greatly over the last 50 years or so. This allows engines to be built from better stuff, which can be machined to closer tolerances. Back in the 60s, you expected to do a top end rebuild inside of 100k miles. Now we frequently see engines go 250-300k or more without any major maintenance. Computer aided design allows better modeling of fluid flows. Lots of electronics inc cars these days, controlling every aspect of the vehicle. They will even tell you what's wrong with the car, something the 60s mechanic could only dream about.
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.
Modern cars should have a mode that keeps the intake and exhaust open at idle so you can keep the burble lol. Thanks for the answer very easy to understand
That would make them drive like shit at low RPMs. Cars essentially do something similar by pumping in fake noise through the speakers.
Yeah but I hate that fake stuff lol. They wouldn’t be able to make it so that as soon as you press the gas it goes back to normal fuel mapping?
It'd be pretty complicated and be bad for emissions. It's just easier to pump in fake engine noise to whisper sweet nothings into your ears about how massive your cock is through the speakers. Or you can buy aftermarket cams and exhaust for your car.
😂😂😂😂😂
You might want to go a bit further back. They were using turbos and getting massive power from airplane engines in WWII
The Allison V-1710 aka the engine in the p38 lighting, thats a airplane from WWII, makes about 1600hp with 28 liters of displacement and two huge superchargers. The Bugatti Chiron does the same with a 8 liter engine.
By today's standards WWII airplane engines are incredibly weak for their displacement.
There's a big difference between how airplane engines and automobile engines are rated for power output. Airplanes have to be able to put out their full rated power for extended periods of time, without suffering any ill effects. Cars only put out peak power for a few seconds at a time while accelerating. Once the car reaches cruising speed, it may only be using a tiny fraction of the peak power output the engine is capable of.
While the Chiron's engine is undoubtedly more efficient then the Allison, there are some more considerations. The vast majority of piston engine aircraft are rpm limited to 3000rpm or so to prevent the propeller tips from entering the trans/supersonic region.
Automotive engine designers often increase rev limits as a strategy for increasing horsepower - in the Chiron's case it redlines around 6k and generates peak HP, if I had to guess, at around 5300 or so. The Allison would have been limited to about 3k, and as the other poster has said, would be expected to run near peak rpms for longer durations.
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What the he will what?
Ducking autocorrect
The Merlin engine in the Spitfire initially used it's twenty-seven litre displacement to achieve...1000hp.
*sad trombone noise*
I don't suppose many cars could drive at their full BHP until their tank was empty, though, so it's sort of comparing apples to oranges.
I dont know about many cars, but in 1990 they ran a mostly stock Corvette ZR1 for 24 hours averaging >170MPH, setting some auto endurance records. And the car was so worn out at that point, that they continued on for almost 5 more hours
I think I’ve heard that Bugatti ran a veyron at top speed and it drank itself empty in about 8 minutes
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..
HP = Torque * RPM / 5252.
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!
Running water for what, cooling?
A little history, in piston airplanes of old, they discovered that by injecting some water in with the fuel/air mixture you get a denser charge and more power in the combustion. This is important in high flying pistons where you need a fuel with a lot of octane.
https://www.carthrottle.com/post/water-injection-how-does-it-work/
The other way to do this is with tetryl lead, one of the reasons why engines made big power in 1967 and that engine made terrible power in 1980. We solved all of the issues with making big power with unleaded fuel by using electronics and injection.
Water injection is the one tool we didn't use. We still run lead in AvGas even though we have known for generations that you could use water injection as a substitute for lead.
Very interesting. Thanks for the info. But if this system is so good, why has it not been a regular things in use for cars?
Wouldn't want to inconvenience anyone by making them fill up with gas AND water.
Similarly, you can eliminate much of the nitric oxide and other damaging chemicals by mixing diesel with a bit of propane. Propane injection has been used by tuners for years to make their diesels go really fast.
https://www.sae.org/publications/technical-papers/content/872095/
So why don't we do that? Well, because it is more convenient to replace diesel exhaust controls (the blue liquid) every 6 months than it is to add propane every fill-up, despite it being a better for the environment and better for the engine.
Because it's a other thing to break and if the engine is expecting water and methanol to be injected and it fails to do so you will shoot engine parts out the side of your engine.
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.
BlowjobPete t1_iug8cxw wrote
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.