VTEC: How It Works | Science Garage

– VTEC just kicked in, yo! – Oh, God! – In the late 90s and early 2000s, the import scene was super hot. And it seemed like Civic, S2000, and Integra GSR drivers all wanted to make sure everybody knew that their cars had VTEC. So what are they even talking about? What’s kickin in when? VTEC stands for variable valve timing and
lift electronic control. It was invented by Honda engineer Ikuo Kajitani in the late 80s, and it’s an ingenious
way to make an engine more fuel efficient and more powerful. (clapping) But those are opposites. How does VTEC do that? Let’s brush up on some engine basics about how air gets in
and out of the cylinders. So there’s a head sitting
on top of the engine block. And all of the air needs
to flow through it. As the piston goes up and down, it sucks air in and pushes it out through intake and
exhaust ports in the head. There’s these valves opening
and closing those ports, like tiny lids constantly popping off and slamming back down again. In an engine running at 4000 RPM, the valves open and close
2000 times a minute. A spinning camshaft controls the action and timing of the valve. There’s cam lobes all along
the length of the shaft. When we say cams, what we’re really talking about are the lobe. As the shaft rotates,
the cams bump into things that bump into the valve. Different engines use
different things for that. Sometimes push rods, rocker arms, or hydraulic lifters. Some engines use a single camshaft to control all of the
intake and exhaust valves, while others use separate camshafts for each set of valves. Single cam vs. dual cam. The exact shape of the cam determines when the valves open, how much they open, and when they close. For lots of complicated
reasons, that camshaft can totally change the
personality of an engine. Imagine we’re running an
engine extremely slowly, like 10 or 20 revolutions a minute. – That’s impossible. – But, at this slow speed,
we’d want cam lobes shaped so that, just as the piston
starts moving downward in the intake stroke, the intake valve would open. Then, the intake valve would close, right as the piston bottoms out, when the cylinder’s full of air. The compression stroke would happen, and at the end of this, the
exhaust valve would open, with the piston at bottom dead center. And it would close after
the exhaust stroke. But that’s not what happens in an engine ’cause the RPMs are in the thousands. The air’s got momentum, and there’s a lotta other things going on that screw with the air
coming in and getting out to help the engine run. Leaving valves open
longer, helps them maximize the intake of fresh air and
the expulsion of exhaust. In earlier days, there’s really only one possible cam profile. They threw in a camshaft with a certain size cam lobes on it. That got driven by the crankshaft, and that was that. But the cams that make the
best valve timing and lift for slow speed driving
and good fuel economy, well, they’re horrible
for making horsepower and going fast. Specially designed racing cams are big. They open these valves
sooner, close them later than small cams would. We saw in the turbo and nitrous episodes that getting more oxygen in the engine makes more power. That little bit of extra hang time gets in as much air as possible and allows the cylinders to burn more gas and make more power. So big cams work really well at high RPM. But they run like crap at slow speeds. The tricks used to shove
lots of air and fuel in at high RPM are
counterproductive at low RPM. That causes messy, inconsistent
air and fuel delivery. You know that lopey idle
that you hear from cool cars? (engine idling) That’s because that car’s got big cams. (whistling) Fuel efficient engine has small cams. So the valves open just long enough to get adequate power
to get the car going. – That sounds disgusting. – They’re limiting the amount
of air into the cylinder. So they also limit how
much gas it needs to burn. This is all fine at low rev. But when the RPMs start to rise, you’re not able to get a whole lotta air. So that’s why cars built for
good fuel economy are slow. Ha, pfft. Slow. Most people aren’t racing anyway, so car makers usually settle on cam sizes somewhere in the middle. You can call that a campromise. (laughing) Okay. This is where VTEC kicks in. Honda figured out how to run
a second cam lobe profile. Basically, it’s a fancy set of cams that gives you the best of both worlds. Fuel efficiency and power
from the same engine. If cams determine an engine’s personality, VTEC has a multiple personality disorder. The Japanese market Integra came out with VTEC in 1989. And it first appeared in the US in 1991, on the Acura NSX. Japan taxes engines based on displacement, so it made sense in Japan for automakers to think of new ways to make
efficient little engines that could still pack horsepower. Here’s how it works. Honda uses dual overhead cams. And in a VTEC engine, larger cam lobes sit between the normal-sized
ones on the intake cam shaft. Rocker arms are the middlemen between the cams and the valve. As the camshaft rotates,
all the cams are bumping up the rocker arms. At low and mid-range RPM,
the rockers that pair with the standard cams are the only ones actually moving the valve. The bigger cam’s rockers aren’t connected to any valves. They’re basically flapping in the wind. So as you’re cruising
at 25 in a school zone, the engine runs frugally, using the moderate valve timing set by standard cam. When you hit the freeway on-ramp and your right foot starts feeling heavy, you want bigger cams and more horsepower. The car’s computer’s been
keeping tabs on everything. And when it sees the right combination of engine oil pressure, engine temperature, engine speed, and throttle position, it decides to grant your wish. VTEC is go! – Aaaah! – The ECU shoots a signal
to a solenoid control valve that pushes the hydraulic pin through normal cam’s rockers and into the big cam’s rocker. These locks those previously
independent rockers together, and, when the big cams hit,
they push all the rockers down and take over the valve control. Now, the normal cams are
the do nothing slackers, while the bigger cams start
opening the intake valves sooner, opening them further,
and closing them later. Suddenly, you’ve got
more air and more power. When you let off the gas a bit, and the computer decides you don’t need the extra grunt anymore, the hydraulic pins retract
to let the rockers uncouple, and the engine goes back
to running on the small cam and just sipping fuel. And now they have i-VTEC, which combines multiple cam sizes with
continuously variable valve timing for even more performance. Amazing. – I was sleeping down there. I’m a bunny. – Guys, dudes, guys, dudes, smash the subscribe button. Thanks to Skillshare for
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link in the description get the first two months for free. So go to skl.sh/sciencegarage2 or click on the link in the description. Go get skilled: Skillshare. The more people who subscribe to Donut, the more cool videos we get to do. You can follow me @BidsBarto. You can follow Donut @DonutMedia. You wanna learn more about
getting air in an engine, check out this video on turbos. You like VTEC, check out the up to speed on the S2000. Don’t tell my wife about cam timing.

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