Saturday, February 25, 2017

VVT-i Explained

VVT-i, or Variable Valve Timing with Intelligence is Toyota's name for the subject at hand. Other manufacturers have other names for it.

Now, what's really fun, is that all modern cars having timing advanced adjustments on the fly, but being able to adjust the timing of when valves actually open and close is revolutionary for the time if you ask me.

Timing advanced, more fully explained, then what's in the video: spark timing, or timing advanced, can be changed at the flick of PCM's choice to generate more power. Under heavier loads, you can't have as much timing advance, or you get knock.

Timing advance is just a related point however. With VVT-i, changing when the intakes open and close was added more as a way to lower emissions, then it was to gain that much power. It really only gives like 5 points of bHP, or horse power at the crankshaft, and even less, only a few horsepower at the wheels. When it advances when the intakes open, it actually doesn't let the engine draw in as much fuel and air. This makes idling these cars much more efficient then their predecessor. This engine concept has been around since the 19th century, but only now can we have a more efficient engine AND a more powerful engine at the same time.

The other reason for better emissions however, is that a later intake means that the exhaust doesn't escape as well so it can be Toyota's way of not having an EGR system. The inert gases reduce combustion temperatures, decrease NOx, if this the example engine even is capable of making NOx, I'd be surprised, but these are the normal functions of EGR. On bigger, badder engines, without EGR, you'll pit your pistons, so let's not just hate the fact that they can clog up or make our intakes dirty. They have a valuable purpose for engine longevity as well!

And now to the YouTube segment today of our article!

Shown by a Toyota Corolla 1998-1999 vs 2000-2002 Engine - Chevy Prizms are the "same" except for these changes across those 2 year zones. What's really interesting, is this engine has a design change but it's the "same" car from 1998 to 2002. It's all the 8th generation of Corolla.

See a VVT-i engine versus the same one without!

By AutoBravado, also DE Nichols on YouTube.

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