72 votes
Accepted

What actually happens when there is not enough oil in a car engine?

Engine oil does much more for an engine than lubricate. It provides cooling, cleaning, and a bunch of other chores. You already know engine function is degraded when you run out of oil. Let's see if ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
58 votes
Accepted

Why aren't electric forms of heating used in internal combustion engines

Because it wouldn't be very efficient. The main advantage of internal combustion engines is that the energy density of their fuels (gasoline, diesel) is very good. You can go a long way on a ...
raydowe's user avatar
  • 3,012
54 votes

Is revving the engine to redline on idle at morning bad?

If your engine even has a problem carboning up, you don't clear it at cold start. Nor do you clear it by spinning the engine to redline. "Revving" isn't meaningful to diesel engine performance the ...
Harper - Reinstate Monica's user avatar
51 votes
Accepted

What is the point of the exhaust?

Safety, comfort, noise and space are the things that come to mind. Safety Exhaust gasses are hot as hell. Hot enough that we put heat shields all over the exhaust line. In engines, we are actively ...
Becuzz's user avatar
  • 666
50 votes
Accepted

What are the benefits of a lightweight flywheel and why aren't they lightweight already?

The main advantage to a lower flywheel mass on race cars is that the reduced mass allows the engine to rev more freely. The overall weight loss to the car is really not the key thing, it's letting the ...
cdunn's user avatar
  • 9,296
47 votes
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Is revving the engine to redline on idle at morning bad?

Yes, this may be bad. The oil is not yet at the operating temperature, and the same is true for engine parts as well. I wouldn't redline a cold engine with cold oil. Your intention to clear carbon ...
juhist's user avatar
  • 14.5k
46 votes
Accepted

Why is engine displacement frequently a few CCs below an exact number?

There are regional taxation and tariff issues associated with displacement Manufacturers will intentionally keep their displacement just under a limit that may increase their local/regional taxation ...
DucatiKiller's user avatar
  • 32.9k
44 votes

What is the point of the exhaust?

Well, we can have a pipe going out the front of a car as in this design here: or its heavier predecessor: Arguably, the aerodynamic properties are not optimal in both, but here is a similar approach ...
the-wabbit's user avatar
40 votes

Why are engines labeled as 2L or 3L?

When they put "3L", which stands for "3 litres", it is the approximate displacement of the engine. Displacement is the swept volume of all cylinders combined. Swept volume of the cylinder is if you ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
39 votes
Accepted

Why do manufacturers detune engines?

I'd be tempted to restate the question as "How do vehicle manufacturers decide what to tune for?" For the question as asked, there are a lot of possible reasons, and probably no way to know in a ...
dlu's user avatar
  • 14.5k
36 votes
Accepted

Do cars consume less fuel when in Neutral?

If the car is equipped with a modern fuel injection system, it will likely use less if left in gear and allowed to run against the transmission with no throttle as modern fuel injection systems can ...
Steve Matthews's user avatar
34 votes
Accepted

We have fuel injection, why not air injection?

Simple reason: volume. @ 14.7:1 stoich, your input into the cylinder would need to be 14.7x bigger (or push that much more) through a nozzle than you would the fluid which is fuel. You state it would ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
33 votes
Accepted

Why are the blades of car radiator fans unevenly spaced?

It isn't something restricted to old vehicles; my Lumina has fans like this, though not as irregular as the picture shown in the question. As far as I can recall, the chief reason cited for this by ...
Zaid's user avatar
  • 39.1k
32 votes
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Why does a gas engines torque and horsepower curve always meet at 5252 RPM?

It's just math, and is because horsepower is defined (in terms of torque) as 550 ft·lbs per second. A single HP is 33,000 pounds moved 1 foot in 1 minute (as per James Watt, that's the average of ...
Mark Brackett's user avatar
30 votes
Accepted

5-Stroke Engines - What are these things?

What is a 5 stroke engine? They tend to consist of only three cylinders rather than the more traditional 4 stroke, 4 cylinder engines that many people are using today. There are two small small high-...
Max Goodridge's user avatar
29 votes

What are the benefits of a lightweight flywheel and why aren't they lightweight already?

cdunn's answer is spot on. To add a bit (especially for cars), in a race car you often want to be dropping from something like 7000 rpm to maybe 5500 rpm (or an even higher band, depending on the ...
J...'s user avatar
  • 692
27 votes

Why do we mostly use fossil fuel instead of a more reliable and larger sum fuel?

What you really want to look into is Energy Density. So called "Fossil Fuels" have a very high energy density, which is very important for a vehicle fuel since you have to load it and carry it around ...
JPhi1618's user avatar
  • 13.2k
26 votes

We have fuel injection, why not air injection?

You have almost but not quite described the operation of either a Turbocharger or Supercharger. The idea of the air under pressure being injected from a common fuel rail would likely not work as it ...
Steve Matthews's user avatar
24 votes
Accepted

What is a head?

tl dr: Cylinder heads (commonly just called "heads") are the big piece of metal which caps and seals the end of the cylinder bore. Types of Cylinder Heads: There are three basic types of cylinder ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
24 votes
Accepted

What is crankshaft grinding and why is it done?

Grinding a crankshaft is a process of removing material from the journals in an effort to refurbish and reuse an expensive, yet vital component of an engine. It is usually done during the process of ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
23 votes
Accepted

Why or why not increase engine efficiency by running the car "fuel-lean" (using a turbo or supercharger)?

Lean ≠ More Air I believe the source of the misunderstanding is in how the term "lean" is being interpreted. A lean mixture doesn't indicate the presence of more air. It indicates the ...
Zaid's user avatar
  • 39.1k
23 votes

Why do we mostly use fossil fuel instead of a more reliable and larger sum fuel?

While energy density is a rather nice property of gasoline and diesel, it's not the primary driver of their use. Instead, the primary driver is a rather practical one: they're cheaper. On the ...
R.M.'s user avatar
  • 331
22 votes
Accepted

What mechanical revolution is measured in "RPM"?

Ok, let's start from the same picture so we're on the same page: These engines are four stroke engines, which means the piston goes up and down a total of 4 times, twice up, and twice down for each ...
cdunn's user avatar
  • 9,296
20 votes
Accepted

What are the benefits of a dry sump?

You Asked What are the benefits of a dry sump? Simply put a wet sump crankcase has oil sitting in the bottom of the crankcase. It's affected by various forces as the car or motorcycle is driven. ...
DucatiKiller's user avatar
  • 32.9k
20 votes

Will higher octane fuel improve towing power?

That is a great question. I believe the true answer here is "it depends". Like so many other things you can do with your vehicle, if your vehicle cannot use the higher octane fuel, it won't benefit ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
20 votes

Why do manufacturers detune engines?

Great answers, but there is also one more reason for manufacturers to detune engines: can the vehicle take the torque? A van isn't built like a sedan, and it's frame is built to handle weight (...
tlhIngan's user avatar
  • 12.2k
19 votes
Accepted

What is regenerative braking and why don't we use it?

tl;dr: We do. It's just expensive. One of the differences between electric and chemical energy motors is that the electric systems make it much more convenient to capture and retain energy (e.g., a ...
Bob Cross's user avatar
  • 24.4k
19 votes

What actually happens when there is not enough oil in a car engine?

In most engines, when you fill the oil, it drains into a reservoir on the bottom of the engine known as the oil pan. The tube for the dipstick goes right down into this reservoir to measure the level ...
JPhi1618's user avatar
  • 13.2k
19 votes
Accepted

Aluminium engine vs Cast Iron engine

You've already stated the main reason for the aluminum blocks which is the weight reduction. It is the same reasoning which has led Ford to produce their F-Series trucks with an aluminum body: weight ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
19 votes
Accepted

Does stopping the engine while it is still moving/turning damage my car?

What will happen is dependent on the configuration of your vehicle. Automatic transmission - Due to the torque converter, the engine will just stop. This is bad for the transmission, because the ...
rpmerf's user avatar
  • 8,403

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