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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.

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frakc t1_iuh672g wrote

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

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vferrero14 t1_iuh6uop wrote

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.

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DonaldTrumpTinyHands t1_iuhaq1a wrote

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.

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vferrero14 t1_iuhdfjw wrote

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.

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series_hybrid t1_iuhr5tq wrote

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.

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DonaldTrumpTinyHands t1_iuhamu0 wrote

I think the most significant is higher RPM. pushrod engines have a tendency to fly apart at higher RPMs, whereas DOHC do not.

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Kahless01 t1_iuhtp7l wrote

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.

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DonaldTrumpTinyHands t1_iuiek61 wrote

What variety of that engine did you have? Since I read the stock Ford 289 redlines at 5500.

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series_hybrid t1_iuhqlik wrote

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.

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OSRSTheRicer t1_iuiw9jd wrote

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

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Photodan24 t1_iuhv7f2 wrote

Transmissions that have upwards of eight forward gears also help efficiency by keeping the engine in its most efficient rpm range longer.

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Silvster88 t1_iugwmqb wrote

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.

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86BillionFireflies t1_iuhjyuj wrote

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?

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Silvster88 t1_iuhlmoi wrote

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.

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