VVTI

[Victoria]

What exactly is VVTI?

[RomanV]

It stands for Variable Valve Timing with Intelligence.

Basically the cam belt runs around an oversized cam pulley, that is full of smoke, mirrors, and magic.

It can rotate the angle of the cam shafts inside this mechanism, so you get the best cam timing at no matter what RPM.

As opposed to fixed cams, which are optimised for one RPM range.

So you get more power across the entire rev range.

[Victoria]

well that makes a hole lot more sence... i got told it was variable valve timing injected... therefor the length of time the valves closed for was slightly longer to get more a build up of preasure b4 the sparkplugs did their thing...

[RomanV]

Well yeah, the engine more than likely can alter the spark timing, to get the most power out of the cam timing.
Every VVTI engine that I have seen has individual coils, so it can advance the timing all it wants.

However the cam still opens and closes for the same amount of time,

it can just open and close earlier, or later in the combustion cycle.

eg. You want to open the intake valves earlier at higher RPM, so the VVTI mechanism rolls the cam 'fowards' to suit.

20 valve engines have VVT.... Not VVT-I.

This can switch the cam between *only two* slightly different angles, based on load, rpm, etc.

But it isnt freely varaible within the 60 degrees or so of movement that the VVTI can acheive. (Although with the factory setup, the cam angle only changes 20 something degrees IIRC. The mechanism is capable of moving through 60 degrees however.)

[RomanV]

P.S.

Here is a good read on VVTI.

http://www.billzilla.org/vvtvtec.htm

[Victoria]

thanks for the help