How VTEC Works - A Simple Explanation

hello everyone and welcome I am currently surrounded by VTech there's VTech in this s2000 in this Honda Accord and in this Honda Civic type-r engine in front of me so in this video we're gonna be getting into what is VTEC and how does it work now in order to understand VTEC we need to understand engines and engines need at least three things to function they need air they need fuel they need compression and in the case of gasoline engines like this Civic type-r engine you also need a spark now VTEC deals with the air portion of this equation of those four things that the engine needs so now we know what an engine needs and it operates on four strokes so the first stroke is intake where the piston moves down and it pulls in air and fuel the second stroke is compression where that piston moves up and it compresses that air & fuel mixture the third stroke is the power stroke where a spark plug ignites that air in fuel mixture pushing the piston down and then the final stroke is the exhaust stroke where the piston moves up pushing out those spent exhaust gases now VTEC can optimize airflow during those strokes so both during the intake stroke as well as during the exhaust stroke you can use VTEC to maximize and optimize the airflow that you get going through the engine now before we look inside of the type or engine let's look at a simplified example so here we have a cylinder head and we have valves to allow air to come in and out of the cylinder so here we have the intake valve which allows for air to go in and then here we have the exhaust valve which allows for air to go out now how much these valves actually open is dependent on the camshaft so the camshaft is going to be responsible for opening and closing those valves so you can see these cam lobes on the camshaft right here so this is rotating and as it rotates it will force that valve open now the greater the height on this lobe right here that forces that valve open the more it's going to lift and so the more that valve lifts open you can see the more airflow it will allow to come in or out of the engine now if you can put more air into an engine you can put more fuel into that engine and then you can make more power so now let's take a look at how the elves work on the type or engine so here we can see two different camshafts this rod running along right here and right here and a traditional camshaft will look like this one right here where you have just a single cam profile that is used to open and close the valves versus a VTEC camshaft which you have right here which has multiple profiles of different heights and different lengths that will open and close those valves so here we can see the VTEC camshaft and here are the two valves that this camshaft is responsible for opening and closing and as you can see it has two different cam profiles to choose between so it can use this inner cam profile which has a higher lift on it or it can use this lower cam profile here on the outside it'll use both of these simultaneously to open these two valves so it can switch between these two profiles so why might you want this lower profile well you'll use the lower profiles at lower rpm so at lower rpm you don't need as much air and so because of that you use a lower profile and that means that the air is coming in faster by restricting the air flow the air is forced to speed up and by speeding up that air it mixes with the fuel better and because it's mixed with the fuel better you get more efficient combustion now at high rpm you want to make as much power as possible so you want as much air coming in the engine as possible so you use the higher lift cam profile and that allows that valve to open up more and you can force more air into the engine and thus use more fuel and make more power so how does VTEC actually work well at lower rpm this outer profile as mentioned will be responsible for opening and closing the valves and it does that by pushing these outer rocker arms down this Center rocker arm is disconnected from these two outer rockers and so this center cam profile is moving this Center rocker up and down but because it's not attached to the outer rockers which are attached to the valves it's not actually influencing the lift of the valves so they're lifted with the lower cam profile now once the engine starts spinning up faster you're going to want to start to use this higher lift cam profile and so what happens is oil pressure at those higher engine RPMs will force a piston to Lock these rocker arms together and so where previously this camp profile was just moving this rocker arm up and down and it wasn't doing anything now it is locked to these rocker arms which are of course attached to the valves so now this center cam profile is responsible for opening and closing the valves and because it has a higher lift the valves will then have a higher lift and you can continue to use oil pressure to change if that piston has locked or unlocked these rocker arms to choose which cam profile you want to use now if you've been paying close attention you'll have noticed that VTEC only exists on this engine on the exhaust side so only for operating the exhaust valves versus the intake valves up top which just have a single cam profile different from many of Honda's previous performance engines which have VTEC on both the intake and the exhaust so why in this case is there VTEC only on the exhaust side well the reason is that this engine is turbocharged as you can see right here so the turbocharger makes it really easy to force air into the engine it's easy to get that air in without using that extra lift profile but then once you've had combustion occur and those gases have expanded you have a really high pressure in that cylinder and so by using the higher lift profile it's easier to force those exhaust gases out and the other thing you have to work against not only do you have that higher pressure after combustion you also have to force that air through a turbocharger so by using the higher lift profile it's easier for that airflow to move out move through the turbocharger and out the exhaust thank you all so much for watching and if you have any questions or comments of course feel free to leave those below you

Channel: Engineering Explained

Views: 1,755,124

Rating: 4.943316 out of 5

Keywords: vtec, honda civic type r, honda s2000, honda accord, type r engine, type r crate engine, how VTEC works, how iVTEC works, what is vtec, horsepower, torque, boost, turbo, honda civic, honda civic si, engineering explained, f20c, k20c1, DOHC, camshaft, engineering

Id: tSCuRXnfLuI

Length: 6min 20sec (380 seconds)

Published: Sun Sep 16 2018

Reddit Comments

[u/Georgeofthebunghole]

At least if Beto O'Rourke's bid for Senate doesn't work out, he's got this YouTube channel to fall back on.

[u/hawesome45]

After all these years I now actually understand how V-tech works! Top tier video, thanks for sharing 🤙

[u/[deleted]]

I like Honda four cylinder engines I have always found them to sound more refined versus the competition (looking at you Toyota).

[u/SsgGotato]

No, VTEC works by having a sticker on your dash and/or having any Japanese vehicle, then is followed by preemptively saving "wait for VTEC". Only when all these requirements are met u successfully activate VTEC

[u/Rippthrough]

Simpler explanation:
"NEEEEEEEEEEOOOOOOOOOWNNNNNNNNN"

[u/godofthesserengeti]

Yeah donut media did a great job of explaining how

[u/smittydust]

Salt and pepa is here.

[u/roboticWanderor]

I always wondered how they get the different cam profiles to switch. It explains its some oil piston, but how does that mechanism on the bigger cam follower work?

[u/hussainc4s]

Didn't understand but thank u the vid