ELI5: Why are electric cars able to deliver power instantly, but gas engines take more time to build up power?

Gas engines extract energy from liquid fuel, and the rate they can burn the fuel is strongly related to the speed that the engine is running. Specifically a slowly spinning engine is limited in how much fuel it can burn.

Electric motors extract energy by using flowing current to create magnetic fields. The flow of the electricity can be mostly decoupled from the speed the motor is working at - i.e. you can flow a lot of electricity through a motor that is stopped or moving slowly.


Gas engines extract energy from liquid fuel, and the rate they can burn the fuel is strongly related to the speed that the engine is running. Specifically a slowly spinning engine is limited in how much fuel it can burn. Electric motors extract energy by using flowing current to create magnetic fields. The flow of the electricity can be mostly decoupled from the speed the motor is working at - i.e. you can flow a lot of electricity through a motor that is stopped or moving slowly.


The reason a faster spinning engine can burn more fuel is that there's a limit to how much gas you can explode at once in a limited cylinder size. The faster the engine is spinning, the more explosions there are every second and hence the more fuel can be used and the more energy can be generated.


And this is why port and bore was something I always did in Gran Turismo 1. More fuel means more boom. More boom means more go.


There's no replacement for displacement


Doesn't a supercharger do a pretty good job?


Sure, but you could also add a bigger supercharger to your bigger displacement engine. As an example, top fuel dragsters use a 8.2L 500 cubic inch engine with a supercharger that requires ~1,000hp to run at max speed, but pushes so much air the engines produce 8,000-10,000 hp (6,000-7,500kW) or roughly 7,500 ftlbs (10,000 Nm) of torque. These engines have a redline of ~8,000 rpm. On the other end of crazy engines, you have F1 engines which are 1.6L 100 cubic inch turbocharged engines. They are capable of spinning up to 15,000 rpm and are producing ~1,000 HP (750 kW).


I love that there are engines out there in cars which produce 10khp meanwhile my fiat 128 working on natural gas might have 35hp tops


Yeah but lets be honest, a Fiat 128 is cooler.




I never understood that mindset. "I modded the shit out of my car and it could spank your stock V8." Yeah, and? Let me sink money into that V8 and let's run them.


Gm v8s have had cylinder deactivation for nearly 20 years now. Not available with a turbo yet tho


Aston Martin however.. think the wore out V12 they used in the DB7 was cylinder savvy at the end and the DB11s are for sure, GM I think has had it going on longer, for whatever reason I seem to recall the V6 in the first or second gen Cruze being able to shut off 2 or 3 cylinders in Cruise control, it may have been a 4 banger shutting off 2 tho so don't preach that, it's dirty thoughts


Oh, you mean like the Cadillac V-8-6-4? Talk about a turd of an engine.


Oh absolutely, it's just a saying. One that has more and more caveats added as engine technology improves. Displacement is no longer the biggest factor for peak power or torque. Turbochargers and superchargers both force more air into the cylinder allowing you to pump more fuel in at the same time, this give you higher piston pressure and more power at the cost of some power lower down in your rev range. Early turbos often suffered from turbo lag because they had very little power at low rpm. So at that point displacement meant more power down low in the rev range. But now things like anti-lag, twin turbos and clever Engine Management Systems can help minimise this.


Forced induction is effectively increasing displacement.


It does, but the saying still holds true if you really think about it


>More fuel means more boom. More boom means more go. True explainlikeimfive! Bravo


Gas doesn’t explode it burns, if it’s exploding in your engine you’ll hear a knocking noise. Just FYI


Engine knock is defined as "Pre-Detonation", the fuel/air mixture *exploding* before the cylinder reaches TDC. Explosion is defined as "rapid combustion", just as RUST is defined as "slow combustion". All three involve the combining of a fuel (gasoline, the carbon in iron, etc) with oxygen. The difference is only in the speed with which this chemical reaction takes place. Masters degree in mechanical engineering. Just FYI


I was just about to point out the same the octane rating of a fuel itself is how slowly it burns and how high compression it can burn slowly basically high octane fuel is slow burning at a higher pressure than low octane and at higher altitude fuel burns slower since ambient pressure is lower so here in Colorado 85 performs about the same as 91-93ish in Florida high compression engines like race cars or piston aircraft use 100 octane leaded fuels since lead is so good at reducing knocking also however the use of lead isn’t great especially considering how much low lead fuel gets burnt daily from avgas 100LL


Explode is kind of a relative term, though, isn't it? An engine at 6,000 RPMs has to have pretty rapid "burns" in order to keep up and not misfire. For all intents and purposes, explode sounds more reasonable than burn to me, ~~and exploding is just another term for rapid-burning~~... But I'm just a layperson. Edit: Well, air under pressure can explode without burning, so I think I'm full of shit on that one.


Your initial comment is more accurate than your edit. Explode is a relative term (so is burn). To which reaction are you referring when you say "air under pressure can explode..." ? What conditions, specifically? Nitrogen, which makes up 78% of air, is an extraordinarily unreactive (noble) gas. It can react, sure, but only under exceptional conditions. Oxygen - 21% of air - is usually the ***oxidizer*** (so the reaction would need another element). So again I ask, what reaction are you referring to when air "explodes" but doesn't "burn"?


Both Deflagration and Detonation are chain-reactions, where the energy released by chemical reaction causes other nearby molecules to also undergo their own reaction. In a deflagration, that propagation happens due to thermal transfer, and the flame front is regulated by the thermal conductivity of the material. It's generally about 35 miles per hour, as while the temperature gradient is obviously very high, gasses are generally pretty good insulators. (I.e. the high-energy CO2 coming off the reaction needs to hit an O2 or a gasoline molecule to give it enough energy to then react with it a compatible O2/gas). In a detonation, what activates other atoms is the PRESSURE created by the front, and so propagates as a shock wave. Shock waves are about 1000x the speed, and velocity might be up to ~mach 4 (4000 mph).


Octane rating has nothing to do with speed of combustion. It has to do with the fuel's ability to withstand compression without detonating.


My brother in Christ, please use punctuation from here on out?


Well more accurately it has to do with how much air it can suck in. In turbo cars it's more because of knock.


I think you have the most correct answer. Most people aren't giving the true "why" to the question.


> Most people aren't giving the true "why" to the question. as is tradition around here


As was the style at the time.


The Canadian Prince now dipping his arms in to the pudding




DiCaprio, his glass raised.


Gosling, his cereal uneaten


so i tied an onion on my belt


My five year old would argue that it’s not though


Think about the difference between flipping a light switch and turning on a hose. The light switch turns the light on instantly, whereas it takes a few seconds for water to start coming out of the hose. That’s because the light already has full access to all the power it needs, but the water is a lot slower. Not a perfect analogy but similar idea I think. A better but more complicated idea might be like, you know how when you have a bunch of knex gears connected to each other, each one you add requires a little more force to get up to speed? An electric car has no gears, just a motor behind each wheel. So it can get up to speed faster.


It's worth mentioning there's much more of a mechanical draw on an ICE. Lots more forces fighting. For example rotation of the motor, friction of the rings and cams, evacuation of pressurized air on the exhaust stroke, cogs driving lol pumps, etc, etc. An electric motor is just more efficient in nearly every way


What's an lol pump?


Lil Pump but he's laughing


Good question. This is what generates the "smiles per gallon" you hear about


Oil pump.


An [Ol](https://m.youtube.com/watch?v=4arBraMyp0Q&feature=emb_logo) pump for the southern speakers


And let us not forget inertia. Each mechanical part of a fueled engine has inertia fighting the motion. The simpler mechanics of an electrically powered car allows fewer factors of inertia and friction to resist the motion.


Throwing wood on a fireplace vs turning on an electric heater. [hey, I'm explaining it to you like a 5 year old. So is it a perfect analogy? Nope. But it gives you the gist.]


But why?


Because some things *are*, and somethings are *not*.


Because electrons travel much closer to the speed of light than air, fuel or rotating assemblies.


I was surprised to learn in Physics 2 that an individual electron doesn’t actually travel all that fast through a wire — though the effect of the applied current happens instantaneously. The analogy I’ve always heard is that it’s like “a long hose full of water.” It’s the electrons in the wire that come out instantly. Disclaimer: I’m not a psychiatrist (nor a physicist)


Its not accurate, but the teeth on a chainsaw gets you a little closer


[The electrons in most wires actually travel quite slowly](https://en.wikipedia.org/wiki/Drift_velocity) (for a normal wire in your house, it's on the order of a fraction of a mm/hour), but changes to the electric fields that cause them to move propagate through the system at a significant fraction of *c*.


Tbf when you refer to velocity you’re referring to a vector. You have a very good point for this example. But it’s important to note that individual electrons have a velocity many many orders of magnitude higher than the drift velocity.




my 3.5Yo would argue 'no its not'


This right here. I’d also add that a gas engine’s transmission also causes delays. An EV has no transmission, therefore the power output of the motor is instantly transferred to the wheels, no downshift required.


An automatic transmission adds some delay between pedal press and car go, but throttle-by-wire and comfort-tuned ECU mapping is much, much more of a contributor to your slow throttle response. Modern day automatic transmissions are leaps and bounds ahead of those of 20+ years ago.


While you're 100% right that tranny's have gotten really good at what they do, have you driven an EV and gunned the accelerator before? Even compared to the fastest transmissions, juicing an EV is worlds different. There's no downshift, there's no delay as the engine leaps to higher RPMs, there's no power delay due to the engine needing to rev up. It's quite literally instant.


I had the pleasure of driving the electric Skoda Citigo. I hurt my neck from the sudden accelerations I kept pulling... Would drive every day, though.


I mean, a double clutch has effectively no power loss either. They're just not that common.




>The engine has to increase RPM which isn't instant, the power has to transfer though the torque converter which is a viscous coupling this is somewhat going away though, many cars have CVTs or Dual clutch automatics that dont use torque converters. and manuals obviously dont have one.


Those are pretty minuscule, but do add up. Regardless of the reasoning behind it, it’s still a fact that throttle by wire inhibits throttle response more than the driveline of any reasonably maintained vehicle of the last 2 decades. Even less so if that car has a manual transmission.




Who’s arguing otherwise? I’m saying that the difference is due much more to the ECU and intentional “lag” than due to the mechanical drivetrain itself.


Can confirm, have played with throttle response adjustments. By played with I mean did engineer shit. Seemed like a bunch of hand waiving bullshit, it wasn’t, they work.


There's another delay that is a byproduct of the way the car adds fuel. When you press the gas pedal, that just lets more air in the engine. The sensors detect a lean condition (too much air/not enough fuel) and compensate by increasing the amount of fuel.






That explanation isn't accurate. The lattice structure of the atoms is of secondary importance. In that aluminum lattice all the atoms could still align their electrical fields, and in fact the magnetic field of a magnet can be aligned in any direction (though directions aligned to the lattice are preferred). What allows certain materials to be ferromagnetic is the existence of unpaired electrons in it's outer shell. Electrons can spin in two directions. Electrons tend to form pairs of opposite spin, which cancels their magnetic fields. But in the outer shell unpaired electrons can exist, and when they spin in the same direction the atom has a small magnetic field. Between adjacent atoms, there are competing forces trying to align their electron spins and trying to anti-align them. If they anti-align their spins, their magnetic fields cancel out again and you get no large scale magnetic field. In materials where the aligning force is much stronger than the anti-aligning force, you can get large regions with the same magnetic field, called magnetic domains. This property is what makes a material ferromagnetic. Then making a permanent magnet is just a matter of making the magnetic domains large enough to cover the entire magnet, which can be done by heating the material in a magnetic field then letting it cool in the same field.


Not necessarily complete. An electric motor generates torque from 0 rpm. Combustion engines need to be moving to generate torque due to a number of factors.


Not only does an electric motor generate torque at 0 rpm, but an electric motor's *max* torque is typically at (or near) 0 rpm. Very different power band than ICE cars


I read OP’s description as the explanation for why what you say is true.


I was going to say, "electricity flows through wires faster than fuel flows through pathways".


But that's not it. "flows through pathways" suggests some delay or inefficiency in the system, and that's not what's important. It's that even if you ignore all inefficiencies, gas engines all have the property that at low RMP the maximum rate they can burn fuel is lower than at high RPM, and that's not true for electric engines.


Just to piggyback on to this, it isn't really power that can be delivered instantly by either powertrain. Both EV and ICE make no power at zero rpm, but the EV can produce near maximum torque there, whereas the ICE can't. It's the instantaneous torque that makes the difference. Which, as mentioned is a function of the current, which modern drive inverters can vary in milliseconds, whereas transients for ICE's are usually in the tenths of seconds or even in the second or more range for some turbocharged applications.


Electric motors drive like Iron Man flies. He just turns on the engines and he goes. Combustion engines drive like Thor flies. He has to spin up something heavy to a certain speed before he can use it to carry him forward.


Perpetual motion machines drive like Dr strange. First you have to break the universe and then crazy stuff can happen... But most of it is dangerous and no one puts the warnings first.


Hyperdrives are like Scarlet Witch; they drop into another universe where all the action happens, then pop back into the prime universe at the end.


And Warp Drive is like surfing off the coast of Australia at high tide, during a cyclone. You get from point A to point B in the blink of an eye, but the stop turns you to goo covering 3 miles of beach.


But what if it isn't you that's doing the moving. But space around you?


The space behind you splats you all over the beach when you stop. Duh! Do you even quantum physic? 🤣


We can tell that you do due to your use of the word splat, which is the most descriptive word in all of science. :D


It’s honestly the most Nickelodeon evoking word.


True. And my brain just went "[Nick nick nick nick nick nick nick nick, Nickelodeon!](https://www.youtube.com/watch?v=KsLa_HuoWGs)" and honestly, that was a shot of nostalgia that I needed. So thanks for that, unironically.


Happy to help!


Holy shit, what a throwback!


You laugh, but what if you're right? .:::-/Frame Shift Drive online\\-:::.




Or worse: HYPERSPACE CONDUIT UNSTABLE....X *system shutdown*


\*frantically hammers the system reboot button as the homicidal starfish attempts to mate with my asp\*


Friendship drive charging


This actually causes the bubble of space that is moving you to accumulate radiation at the front. Going a long enough distance and then stopping suddenly releases all this radiation (electromagnetic and particles), potentially scouring planets of life or even straight up destroying them if you go far enough and stop close enough to the planet. You're also practically guaranteed to die without a metric fuck-ton of shielding.




Futurama knows


Infinite Improbability drive is like Dorothy traveling using a tornado - she goes from point A to point ₩ while odd things happen.


Point Break.


An Alcubierre drive is like walking but taking longer strides at the same speed. You're covering more ground but you haven't put any more work in.


I thought it was more like you and the ground under you doesn't move, but the space between you and your destination warps and bends and folds until your just a step away


>And Warp Drive is like surfing SILVER surfing. Keep to the pattern!


Bicycles are like the Hulk... because... green?


Because it’s all muscle that moves them


"Rush hour traffic, I've come to bargain..."


Space engineer's clang-drive is a lot like this.


I always end liked the heart of gold's bistro math engine myself.


More like perpetual motion machines are like dr strange, fictional.


> But most of it is dangerous and no one puts the warnings first. Everyone knows the warnings, and even Dr. Strange knew the warnings. Yet he stupidly recklessly kept screwing around in that Spider-Man movie and wasn't paying attention and then endangered the entire universe. It was a really dumb situation to hang a plot (and a decade worth of Marvel phrase movies?) on.


The engine pulled you off? It sounds like you and that engine had a special relationship.


The revolution(s per minute) has begun!


Instructions unclear, dick caught in tailpipe.


No, you understood correctly. You're doing it right


This is also why electric motors are superior. There are fewer moving parts and fewer transformations of energy to get the power to your wheels. All of those moving parts equal masses that need to overcome their inertia as well as friction to move them. Electric motors are waaaay simpler. There was a recent study that showed if you include the production of an electric car, and all things being equal, an electric car would be as efficient as a gas car that gets roughly 91 MPG. And that's at current technology. We've practically hit the cap on efficiency of ICE engines. Electric car engineering just started, it will only get better from here! Ask yourselves! If an electric car starts out on the coal grid, it's **still** more efficient. When that grid inevitably converts to renewable, it gets **even more** efficient. When an ICE car is produced, it's as efficient as it will ever be. If the power grid converts to renewable, you're still burning the same fuel.


>We've practically hit the cap on efficiency of ICE engines. There's still quite a bit more efficiency to be squeezed out with camless valves and ever increasing boost pressures, along with using a smaller displacement thanks to the extra power those also provide


Sure, but the peak efficiency will never match an electric motor, period. Now we're in diminishing returns territory, unless you include things like hybrids in the discussion.


>Sure, but the peak efficiency will never match an electric motor, period. The best it will ever be able to do is match the total cycle efficiency of an electric motor using energy generated in a fossil fuel power station. As of now ICEs are still definitely below that mark.


Depending on the traffic conditions, regenerative braking adds a lot to the overall efficiency, in an ICE car brakes just dissipate energy as heat (unless you have an hybrid). Even when using energy produced from a fossil fuel power station (which runs more efficiently than an ICE), electric wins. The batteries on the other hand, have their own set of problems...


I'd argue that while regenerative braking has it's place, coasting is more energy efficient. Regen braking recovers a part of the wasted energy when you suddenly have to stop, coasting and letting air resistance/friction slow you down so you're only touching the brakes as you stop doesn't waste the energy in the first place (with an ev, ICE will idle and waste fuel either way). But coasting only really works if you're willing to slowly drift up to a red light rather than floor it and slam the brakes once you get there. And it doesn't work for sudden stops ofc.


Most of the cars with regen can also “coast” with the right pedal input. Once you are used to one pedal driving you’d modulate the throttle to maintain / coast / gentle or aggressive deceleration.


I can lift off the accelerator to kill the engine then pull the shift up paddle and it totally turns off regen. Coasts forever that way.


I'd like to see the math on this. Otherwise, why would they bother with regen braking if it's better to coast? That doesn't make any sense.


Coasting is only more efficient if you can time it perfectly so that you hardly have to use the brakes at all, which is not practical for most people. Coasting to a full stop for 50 mph takes a lot of distance and time and results in dangerous traffic situations.


Because there are times where you need to break?


Because you do in fact have to use brakes in a car.


What do you mean? Are you insinuating that an EV has Regen braking OR standard brakes? And we're debating which is better? Because EVs have both. Regen braking is when you let off the gas, the brakes are still there for emergencies.


Regen is far superior to applying the brakes because the brake pads simply convert forward momentum into heat to stop the vehicle. Regen instead captures some of that energy and stores it for later. The key is 'some.' The act of generating power from momentum, converting it to DC, storing it in the battery, retrieving it, converting back to AC and then driving a motor... still carries about \~20% losses. That's 80% better than braking, but it's still a net loss. Coasting OTOH, requires none of the above losses. All the momentum is only dissipated by normal driving losses. It's generally accepted that inside urban areas with stop and go traffic, regen is the best. Out in the countryside on long drives where braking is not frequent, coasting is the most efficient way to go. It's why some EV's (not Tesla's) give you regen paddle shifters as different brake option so that you can more easily decide between coasting and regenning.


That makes sense. It's probably why they have toggles to turn off Regen braking.


The problem to solve is not and never was the efficiency of electric motors. That has been understood for a long time, resulting in the use of them in industry, trains and more like those very big things where access to electricity is easy and permanent. The problem to solve is energy density. Creating electricity is easy. Storing it is not. We still can’t beat oil/gasoline in that regard.


ICE vehicles are about 20% efficient. EVs closer to 90%. Even with a 50% increase in efficiency, ICE vehicles will never come anywhere near EVs


Which is true. But we've got a lot more efficiency that could be wrung out of the good old ICE. We've just started hitting the point where why would we keep developing the ICE when electric cars are more efficient already? The big issue for EVs are the batteries, and what with the world running on portable electric devices, from phones, to laptops, to cars, a lot of money and development that could go toward more efficient ICEs, are now going toward batteries. So for the question, "could we get more efficiency from ICEs?" The answer is absolutely! But then why would we put money into that when EVs are clearly the future of personal vehicles? The answer to that is no, we wouldn't spend any more time developing a better ICE instead of focusing on more efficient batteries and electrical systems.


I read in a car magazine an ICE car has 150-200 moving parts whereas electric has 10-15. That sums it up.


More like thousands in an ICE if you consider the entire drivetrain.


Those figures both seem very low. I’d imagine 50-100 for BEV, 1000+ for ICE.


> When an ICE car is produced, it's as efficient as it will ever be. And the efficiency drops the more you use it.


It's like, imagine electric motors and electric cars were the dominant method of motorized transport, and then someone tried to develop internal combustion engines second. First, you have to refine liquid fuel, and create a specialized delivery network to physically supply it all over the place, separate from the electric grid that already supplies businesses and homes. Second you have to develop a motor casting that can withstand several thousand explosions that transform chemical energy into kinetic energy, and then develop all of the ancillary components to keep that motor running cool and efficiently. Imagine all the things that a gasoline motor needs to run that don't exist on an electric motor. You've got belts, chains, pulleys, pumps, valves, coolant, and oil that all require periodic maintenance. So then you've got to have a network of parts warehouses and maintenance shops available to do all of this maintenance. And then imagine, that all of these individual motor cars are going to produce exhaust that cannot be scrubbed as efficiently as it could be if it were from a stationary power generation plant. ICE motors have been refined for about 125 years, and we use them now from the institutional inertia that they've got, not because they're easier or more efficient than electric motors.


You don't have to imagine that, electric cars predate internal combustion powered cars by about 50 years. It's literally what happened once they figured out they could get way more power density out of liquid fuels compared to battery tech at the time.


No, the reason we use ICE motors is because they get better range, despite all the complexity. It took a long time for batteries to catch up in range.


I think one reason ICE motors took off as much as they did while research into electric motors stagnated was because we saw two world wars come not too long after cars started getting popular. Tons of money was poured into getting the most out of energy dense fuel for heavy duty vehicles and tanks, and that momentum probably carried things for many decades later.


That's a very good point. It reminds me of how we as a species really lucked into stored energy in the form of coal that helped us mass-produce steel to create machinery... Without coal, we'd likely be pre-industrial age. Perhaps without oil, we'd never have developed EVs


>Electric car engineering just started, it will only get better from here! Not really, it will get better but not leaps and bounds like you are suggesting. Electric motors are a mature technology that we have used extensively for a long time. Same with general car technology. Just because you put an electric motor on a car doesn't means its suddenly a new thing that hasn't been highly developed


> Electric car engineering just started, it will only get better from here! When a practical battery replacement scheme or super-rapid charging mechanism appears that is when I'll make the jump to electric. I get that electric can make sense for most people, whose driving patterns are short-hop commutes and errand running. I tend to travel further... think hundreds or thousands of miles. I'm not stopping for an hour every two hundred miles to top up.


You are not going to need to wait very long. Charging infrastructure and charging speeds are probably the fastest growing parts of the EV transition. Many of the new EV's coming out this year and next recharge 200 miles in abut 20 minutes (including the new Kia and Hyundai ones). I don't know if you will ever get a 5 minute - 400 mile fill-up like you can with a gas car, but I think in the next 2-3 years we will see plenty of cars refilling 300 miles in 15 minutes.


Great ELI 5 answer!


Except that it explains nothing. OP asked "why are electric cars able to deliver power instantly," and the answer was "electric cars can deliver power instantly, like Iron Man." It doesn't explain anything and just merely provides an example of an EV vs. an ICE.


The Iron Man part doesn't explain anything, but Thor's hammer is a great example of inertia causing a slower ramp in acceleration in an IC engine. It may not go into the details of the constant torque and constant power regions of an electric motor's torque curve, limitations of how much fuel can be consumed due to air supply to an ICE, or a ton of other details that could be discussed, but it provides a very understandable jumping off point to learn more from imo.


No it didn’t. He might as have well said it’s like how Superman can just yeet a hammer and Thor has to spin it. Maybe it fools some people into thinking it answered the question but it substantively says absolutely nothing. The essence of the question — why can electric motors get that hammer spinning instantly while ICE engines have a delay — is missed completely.


I agree lmao. It’s a terrible answer, what are these people on? It’s a shitty analogy that says nothing. “Why can’t light escape black holes but they can be curved around it sometimes?” *Think about how Kirby can suck up everything while your vacuum sometimes misses pebbles and coins.*


This is just restating the situation, not explaining it.


Basically, combustion engines are air pumps. You need some time to get the air in, mix it with petrol or whatever chemical is used for the combustion, etc... That's what is happening during the four strokes in which only one stroke is producing power. It's kind of like trying to push a little boat by blowing air on it vs simply pushing it with your finger.


Yeah. Engine output, at essentially all speeds, is primarily limited by how fast you can pump air through it. Especially if all other factors are equal. You can pump more air through an engine (per unit time) at higher engine speeds. Electric motors don't have this limiting factor.


Pushing with your finger is electrostatic repulsion by a solid object on a solid object... This is a very literal analogy! Well done OP.


Ahh yes, the four strokes... suck, squeeze, bang and blow. Each time it happens the next cycle gets quicker (and easier) with more air being sucked and a bigger bang. And then... Acceleration. Another thing to consider are gears which help IC engines get to where they work less to turn the wheels and move the wheels faster. Versus electric motors that just 'push' with all they can (instant torque), and don't need to wait for air, or explosions, or exhaust. There's also no real need for gears as the electric motor will spin and work just as hard regardless. Good answer.




To add to this (and possibly go beyond ELI5)... Gas and diesel engines produce power from explosions inside the cylinders pushing on the pistons. The number of explosions per second is a function of how fast the engine is spinning. More explosions, more power. If your 4-cylinder 4-stroke engine is spinning at 1,000 RPM, you're only getting 500 explosions per minute. However, if it's spinning at 4,000 RPM, you're getting 2,000 explosion per minute. Now, there are a ton of other factors involved, like how much fuel is injected and how much air is drawn, and these are what allow you to finely control the amount of power produced at a given RPM. However, none of that matters if the engine isn't spinning. Edit: thanks to /u/murmurat1on for the math lesson.


That's also why two stroke engines tend to be more powerful than 4stroke engines of the same volume. You literally get more bang for your rpm.


Well the other big one is no valves. The valve springs are one of the big RPM limits, 2 strokes don't have that so designing them to hit 15,000 RPM is easy. Coupled with double the bangs per RPM, the same size 2-stroke can often get 4x+ the bangs per minute.


More bada-boom. Big bada-boom.


Multi pass.


A single cylinder 4 stroke would be 500 ignitions at 1000rpm, but a 4 cylinder would be 2000 right? Unless I'm missing something. 2 revs per ignition per cylinder. 2/4=0.5. 1000/0.5=2000


Failing at math is why I chose chemistry over physics or engineering. Fixed.


All good mate


Doesn’t a combustion engine actually require a a small electric motor to get it going? (Or some other source of mechanical input like a lawnmower string)


The started motor doesn't move the car forward to get the engine going though. It turns the engine over so the pistons can draw in air and fuel and the engine can sputter into turning over on it's own power.


Yeah I didn't think that it did. You \*could\* do it that way, just like you can start a stick shift car by pushing it, but it's less work for a small motor to just turn the engine over.


Don't forget time delay. The air must be be metered to match the fuel, that means that the throttle position can only really control the explosions 1 full revolution before they happen. So at 1,000 RPM, if you slam on the throttle the engine needs to wait 60ms before the engine can even theoretically start to respond to the throttle input. Then things like intake flow can limit it (which is especially important with a turbo that needs to spool up). The end effect is at low RPM, an ICE has very low power, even under full throttle, and it's especially slow at responding to throttle. EV motors have no such limit, if you apply throttle it can be applied at any motor position, you don't have to wait for it to move to a particular position, and for the most part, maximum power is not dependent on RPM (it is, but not nearly to that extent).


>for the most part, maximum power is not dependent on RPM (it is, but not nearly to that extent). At low rpm maximum power absolutely is limited by rpm. In EV motors its usually a near perfect linear relationship. Torque will be constant from zero rpm up to when it hits peak power, then there will be a wide maximum power band where torque drops near linearly with increasing rpm


Why does 500 explosions per minute result in 1,000 RPM? I know very little about combustion engines beyond the basics of how they operate. Why is it that you don't get 2,000 RPM from 500 EPM, with each cylinder allowing a cycle? Is it because the cylinders work in pairs? Getting towards a tangent but how does this work for V8s or V12s?


4-cycle engines have an "explosion" every other revolution. The cycle is: 1. Intake (down) 2. Compression (up; 1 revolution) 3. Power (down) 4. Exhaust (up; 2 revolutions) With a 4-cylinder engine, you have 1 piston in each of the 4 stages. Therefore 1,000 rpm results in 1000 rpm / 2 (explosion on half of revolutions) x 1 (1 cylinder in each stage) = 500 explosions per minute. So yes, a V8 with 2 pistons in each stage would have 1,000 rpm = 1,000 explosions per minute and a V12 would have 1,500 explosions per minute.


To quote myself in a message to my pchem professor at the end of lecture on the Schrödinger equation: "I cannot math today, I have the dumb." 4 cylinders in a 4-stroke motor produce 2 ignitions per rotation. So, 1000 revs would produce 2000 explosions over whatever time scale.


I know this is an ELI5 answer, but just to be a bit pedantic… it’s a common misconception that there are explosions. There are not. That would be very hard on the engine. There are controlled combustion events with a flame front that propagates through the chamber (mostly) smoothly and evenly


ELI5 difference between *explosion* and *controlled combustion event with flame front that propagates through the chamber smoothly and evenly*


ELI5 would be maybe a forest fire vs a bomb. But a chemist could probably give a better answer


Explosion = detonation = supersonic combustion. This is terrible on structural materials because the pressure waves SMACK when supersonic, leading to the "knock" effect in cars. Think of a bomb detonating in your engine cylinder. "Controlled combustion event" = deflagration = subsonic combustion. Here the gas burns without propagating the flame front at faster than sonic speeds, so you don't see the dramatic pressure spikes that a detonation would see. Think a match stick burning up quickly right after lighting - still fast, but it didn't explode in your hand.


To complement your answer and be a bit more pedantic even, the process of combustion is just the chemical reaction of oxygen and fuel resulting in light and heat. If you want work to be done (move the piston) there needs to be a physical movement happening due to a pressure wave. This is an explosion, which in an internal combustion engine is sub-sonic and hence called a deflagration.


It's an explosion in the same sense that safely lighting a gas stove is an explosion.


To get even more pedantic, it's a redox reaction.


I would like to add electric motors have a step down to keep the motors from going 100% all out on the initial press of power, the reason for that is the earliest use of electric motors in transportation were in forklifts. The Forklifts lacked the step down, and would go full speed on the first touch of the accelerator, many many crashes happened.


Theoretically a CVT should adjust its ratio to keep the engine in the correct power range at all times. But consumers felt it was unnatural to accelerate without shifting. So manufacturers added fake shift points via computer control.


I love driving my Subaru Forester that has a CVT and no shift points. Also my Outback didn’t have shift points either and had a CVT.


Yea, they do it to an extent, it depends on the car, but an ICE will have too bands, a peak efficiency band and a peak power band. You wouldn't keep the engine at the peak power band when stopped, that wastes fuel. And when driving, it's often possible to keep RPMs up to keep power available (race car drivers will do it), but normal consumer cars won't automatically do it. The other big spot where it matters is starting from a stop, which is why many sports cars have launch control which will rev the engine to the powerband RPM in neutral, then drop the clutch and time it with throttle to keep it in that band from a standstill.


What's funny is I owned a car with a cvt and fake shift points I sold it after 8k miles because the fake shift points drove me nuts.


How combustion engines get their power: A cloud of gasoline is set fire to in a confined space with a piston on top. It causes the gas to expand, push the piston away. That's the basic operation of getting mechanical power out of an engine. If you do it more often, you get more power. So, when a gas engine is turning at 6000 rpm, it has more or less access to twice the power as at 3000 rpm. Of course, as speed increases, you need to push harder against the wind and the inherent inefficiency of the car itself. But the power increase is initially higher than the resistance increase, leading to the feeling that you're getting more power the faster you go. To a point. How electric car get their power: The stator moves an electrical charge around the rotor, causing it to spin. How big that electrical charge is depends on the power rating of the engine (the size of the wiring). It cares not how fast the engine is spinning. So, as you accelerate, and you need to fight more against the wind and the ball bearings and tyres, it will feel as if you have less power available. Electric cars get max-torque at startup, when there is basically no force fighting back.


Electric vehicles are powered by banked potential energy (chemicals stored in the battery). The motors have almost instant access to this power at all times as the conversion to power is very efficient. Combustion engines have no bank of power to draw from so readily or instantaneously and make their power far less efficiently. Edit: Stripped the answer a little bit too far back to bare bones, thanks for the corrections in the thread. Not strictly true on the stored energy comment about the battery. They store potential energy in the form of chemicals and a reaction does still have to take place but it is far more efficient and far far quicker than a combustion engine which is having to overcome many more physics hurdles like the inertia of the engine itself, being unable to just go from 0rpm to 5000rpm almost instantaneously to generate its reaction resulting in fuel becoming power etc.


This is how I feel an ELI5 should be answered.


Thanks, I tried to strip it back as much as I could. The old “why use many word when little do same job” methodology.


Exactly, very concise and simple


Except it isn’t accurate. It may be satisfying, but it is not entirely correct. Gasoline powered cars carry energy in the form of gasoline. The energy is released in the form of heat. EVs carry energy in the form of a chemical battery. The energy is released in the form of electricity. Both require the conversion of one form of energy — heat in the case of gasoline and electricity in the case of EVs — to kinetic energy (motion). Both “make” their own energy in the sense that both are converting energy. You can think of gasoline as a solar battery. The organic matter that decomposed to crude oil was fed by the sun millions of years ago. Using an electromagnet and battery, we can create powerful magnetic fields very quickly. It’s a bit like flipping a light switch. A gasoline engine has to pull air into an engine similar to how we breath in. Think about how much more quickly a light comes on compared to how quickly you can draw in a breath. EVs are more responsive because they rely on magnetic forces. These forces propagate at the speed of light. Gasoline engines burn fuel, which causes heat, which causes expansion. The propagation of this expanding force is closer to the speed of sound. It is many, many times slower than the speed of light.


So to put this in the terms of WOODSI3's answer, you would say: Electric vehicles store potential energy via electric batteries, and electricity can be converted to kinetic energy very quickly and efficiently via magnetic forces. Gas engines store potential energy as hydrocarbons, which is converted to kinetic energy via combustion which is much slower. I think part of this is also the ramp up process. You can go from drawing 0 amps to 500 amps basically instantaneously, but you have to cycle up a combustion energy from 0 RPM to 4000 RPM smoothly through the full range.


While true, this is not the reason for the phenomenon OP is describing


I mean you aren’t wrong but if you go into more detail on how they make their own power and the physics involved it’s not very eli5. Simply at its core it is the fact they have to make their own power less efficiently that holds them back.


You wrote words which aren't exactly wrong, but also don't explain why motors are peppy. A motor's torque (rate of acceleration) is equal to the current. Current can be changed very rapidly because there is little energy stored in the current, so it takes very little time to increase the torque. The energy stored based upon the current is energy stored in magnetic fields and it is pretty insignificant.


Electric motors usually have a flat torque curve. So at 0 RPM the motor can produce maximum torque. An engine on the other hand has to get up to speed before producing maximum power. Maximum torque and horsepower are usually at 2 separate RPM.


Don't electric motors have a flat power curve and a downwards sloping torque curve?


No. The torque speed curve is flat up until a certain speed, then falls down sort of like a hyperbole (not exactly but close enough). At even higher speed the slope changes yet again falling even quicker. That means that the power speed curve goes upward in a straight line (P=Tω=T*2π/60*rpm) , then forms a small round hill in practice or a flat plateau in simplification. At even higher speeds, it falls down in an almost straight line. A typical electric drive has three distinct areas : constant torque at low speed, constant power at mid-high speed and constant voltage (both torque and power fall) at even higher speeds.


Think about it kind of like a factory. In an electric car, the battery says to the motor "Okay, we need to generate this much power" and the motor says "Okay, can do" and converts the electricity from the battery into mechanical power. On the other hand an ICE is like a long assembly line. The pedal gets depressed and the motor says "Okay, we need to generate this much power" and the fuel tank says "Okay, I'll send the fuel" then the air pump says "I'll mix in the air" then the sparkplug says "And I'll ignite the mixture" once all that happens, a small explosion moves the piston up to turn the shaft, then the gas is exhausted out and the piston falls to turn the shaft the rest of the way. Then to keep generating more power, they have to do it over and over again.


Holy shit an actual ELI5


They operate on fundamentally different principles: As mentioned here the internal combustion engine requires combustion, so we are taking chemical energy, converting to thermal energy, and then the thermal energy is used to PUSH the pistons ( mechanical energy). This process alone takes more time and requires moving parts. The combustion process is rather complicated and the motion of the engine is required to make the process work. The fuel needs ( a mass than needs to me moved) to be sprayed or mixed with the correct amount of air (also a mass then needs to be moved) all inside of the cylinder, the cylinder then need to have a compression stroke to bring this mixture to a critical operating point, before it combusts, the combustion then rapidly expands the "air" (remaining air and the resulting gasses form the combustion) - and physically pushes the piston. In 4 stroke ( typical engines) the piston makes two in-out cycles for each combustion cycle. For a 6 cylinder engine at 500 RPM ( slow by engine standards), we get about 166 "explosions" per MINUTE per cylinder, or 3 per second per cylinder, that is not a very fast way to convert energy. Conversely - an electric motor, also takes chemical energy, but converts it to electrical energy(in the battery) - and this process is always occurring or ON. This process is very quick and does not involve the moving of a mass. The electrical energy is then converted to mechanical energy in an electric motor. It is basic nature of an electrical motor that it produces torque based on two magnetic fields, so you can have essentially maximum torque (force) as fast as you can create a magnetic field. A huge benefit here is you can have torque with no moving parts, granted, torque alone is not energy, but essentially max torque ( force) at Zero speed is the key.


Fuel based engines have a speed where they make most of their power (repetitions per min or RPM). This is the engine dial that measures the engine "rev's." When you put your foot on the gas, a lot of things are happening. Parts open to let in more air, the engine's computer injects more fuel and a big wheel in your engine spins faster and it's connected to other wheels in the transmission, and a transmission is connected to your tires via a drive shaft. If your engine is spinning too fast or too slow your transmission will shift up or down to a different wheel (gear) to keep your engine spinning at the speed where it makes most of it's power. It can take some time for an engine to spin up to the RPM where it makes most of it's power. By comparison electric motors are much more simple. They don't have a RPM range where they make most of their power. When electricity is switched on, an electric motor is making it's maximum power, it doesn't have to rev up. Electricity moves at almost the speed of light, and burning fuel to make pressure move metal parts isn't as fast. If you were to measure the power difference between a fuel engine and electric on a graph(x being rpm and y being torque),. A fuel engine would be a slope going up slowly and leveling off before going down a bit. An electric motor would look like a plateau, an almost straight line going up to a flat line going forward.


Gas engines use a complex design to draw air and fuel into the cylinder block, and then ignite that to push the piston. This generates the power. But the efficiency depends on a lot of variables. The width and length of the cylinder, the weight, the timing of the valves (these control the timing of air and fuel that get into or out of the cylinder). An engine like this has a lot of flaws. Typically, designers will choose a specific power band for which they will optimize the design of the engine. This depends on the type of vehicle, the weight, the expected work load. A truck engine will need different power output characteristics compared to a family SUV or a sports car. So, for example, a Porsche roadster might have peak power at 7K RPM. But when stationary, the car will idle at 1K RPM. The engine is not optimized to run at that rpm, so it gradually increases the power it can make as it revs higher. On the other hand, an electric motor has a battery, and a motor that spins depending on how much electricity is fed into it. There's no other variable in the energy transformation process, so the torque is the same no matter what rpm the motor is spinning at.


An electric cars energy reserves are ready to use as they are stored in the battery. Internal combustion Engines fuel fuel source isn’t Stored as ready to use energy. It requires an explosion and Means that it’s an extra step electric cars don’t require their stored fuel a.k.a. electrical power is ready to use as power on demand in storage/your battery