So what are the advantages and disadvantages to advancing or retarding the intake cam during different points of the combustion cycle?

With VVTi, Toyota supposedly did this for emissions, but there is power and efficiency to be had as well.

Thinking outloud, it would see best to open the intake valve as soon as the piston hits tdc and the exhaust valve closes. Pumping losses could be minimized, air could be drawn in for the maximized stroke duration and intake turbulence minimized by having some linearity to the air speed increase and decrease?

Any thoughts on this? Anyone with EAPro that could run some sims?

Do you mean in general?



You can't take out overlap and expect to make good power. Variable cam timing manages your overlap so you can minimise reversion at low speed and maximise scavanging at high speed. Not sure if the UZ varies duration/lift?

ED has a dyno somewhere of full advanced and full retarded cam timing, not sure if it was VVT controlled or manually adjusted.

Hi, We only have variable cam timing on the intake cam for most motors, the 2zz and UZ motors included.

Advancing the intake cam to open right after the exhaust valve closes/tdc occurs seems like it would minimize reversion well, and indirectly help scavenging.

Not sure how big the standards cams are, but probably not much overlap anyway. You need to start opening the valves before TDC so they are open enough to flow as the piston heads down. If you retard too far you can hinder flow after TDC, and also introduce reversion at the other end on the compression stroke. You can also purge left over exhaust out of the cylinder during the overlap period under certain conditions.

You're right about retarding the cams at low speed, not sure if it should be right back to TDC though. High speed you'll want to advance more. I think you'd have to play on a dyno.

Agreed ... I may buy a dyno and put it in the garage and then play with this

Hey guy's, you are working on the wrong part of the cycle !

The important part is the close point of the inlet valve, the overlap is a byproduct.

To obtain power lower in the rev range, shut the inlet valve earlier.
To extent the higher rev range, delay the closing of the inlet valve.

Erol