Car Tech 101: Variable valve timing explained

Few innovations under the hood have become as ubiquitous as variable valve timing. Automakers brag about it all the time, but seldom explain it. So Brian Cooley's here to do just that.

[Homer]

This guy does an excellent job of explaining VVT in this video.

[notallthatbad]

This is exactly what I was looking for. No complex explanations or assumptions of what I know and what I don't - just very simple, conceptual and visual explanation. Thank you!

[isaac-zsyz]

I like when someone explains it. especially as good as the man in the video

[Ejeby]

0:36 four valves per cylinder common these days (more area to let the engine breathe in and out)
0:40 problem: a strictly mechanical system operates the same at all RPMs and all engine loads; that is not ideal for mpg, horsepower or emissions ; you want to vary behavior at different points of the engine's rev range ; that's why we have variable valve timing
3:40 solution: variable valve timing dramatically improves how engines raise MPG, increases horsepower, and lowers emissions ; one of the great revolutions in car engineering
1:00 changes three parameters (varies three valve events):
valve timing - at what point in the engine's rotation do the valves open and close
valve duration - how long the valve stays open,
valve lift - how far a valve moves off its seat when the valve opens
1:30 if you leave exhaust valve open longer on one stroke, you blow all the exhaust out, leaving a fully open and clean cylinder to take in the maximum gas and air on the next gulp, giving maximum power
1:44 if you close the exhaust valve a little sooner on one stroke, you leave some exhaust in the cylinder and therefore you take in less air and fuel the next time ; that kind of creates a virtually smaller engine for a moment, and that could give you better MPG
1:58 mechanisms that allow valves to change their behavior 3:28 every carmaker has their own brand of variable valve timing (is this bc patent law makes it too expensive to use a few best practices, or are there good reasons for such variation?) e.g.
2:06 multiple sets of lobes on the camshaft; different lobes of different shapes are used at different points in the engine's operation -- how are the lobes switched?
2:16 change the relationship between the rotation of the crank and the rotation of the camshaft so they're not always locked 1:1
2:25 eccentric cam drives: the engines turning at a certain RPM but eccentric drives on the ends of the cams allow them to accelerate and decelerate their rotation; that gives you a degree of control
2:40 invention - Fiat is credited with first mainstream production-ready system dating to 1969; known today as multiair, seen in the new Jeep Cherokee, now owned by Fiat
2:57 their version of changing valve events using hydraulic pressure out of the oil system (?)
3:05 the most famous form of valve timing is Honda's VTEC

[dogwalk]

damn. don't normally expect to learn that much from cnet. but having this explanation & visual made concepts i've heard about for years make complete sense. thanks!

[Afrocanuk]

Nobody is better qualified to explain this topic than the designers of the 5th. generation Honda Civic powertrain.

[kgardner]

And that's why it's extremely important to keep your oil clean.

[ErusNotitia]

Mr. Cooley, I have watched many of your videos, and I would have to say that you are one of the best individuals at explaining complicated technology in simple terms. Thank you!

[MonteOlsen]

Really enjoy how Brian explains things. Porsche was one of the first to take this to all of its engines with Variocam back in 1992 with the 968. And it works great.

[balisongman]

This is hands down the best explanation ive seen yet. thank you. Ive seen fancy ass 3D videos with excellent graphics and presentation. but i was still left with about as much knowledge as i had before hand

[balisongman]

I can not express how thankful I am for this video. When I got my 1GR FE no one could explain how it worked. The only detailed videos were in Russian so I was completely lost but wanting to understand.

[nestr]

Damn that was informative as hell! Thank you

[NoBody-nukx]

One of the best mechanical explanations ive ever seen. Bravo Bravo...well done

[mubafaw]

Very clear explanation. Straight to the point no BS! Appreciated

[ayvaovaygmail]

This gentleman is very enthusiastic about explaining the idea! Thanks mister! I've learned something new!

[geraldfordman]

Wow! You really explain things well. Crystal clear! Thanks.

[Unclenate]

Fantastic presentation. I own a 95 Lexus LS400 and noticed that a few years later they started adding these to their engines which apparently made the vehicle go up 30 HP. After hearing the term i had to look up what it is and how it works

[citizenplane]

Just by the name i knew what vvt was but i wanted to look up exactly how they change the timing bc im just weird like that. And this guy did a great job explaing it. Wanna see one of the engines with multiple lobes thay shift over work.

[wreidlife]

Quality! Well done! Bravo! Succinctly informative and comedic too. Brilliant. Simply brilliant! Today I learned what in hell v-tech is.

[kevinmcgrath]

Marvellous explanation....great teacher of mechanics and tech