Variable cam timing/phasing.

[atsakiri at ford.com]

> 	Wouldn't having control over the lift and duration be more 
> critical than phasing change? 

True, the production variable cam timing systems previously
described do not vary lift or duration, but they are simple
and durable enough to be in production (some since the early 
'80's).

> If so, why isn't their usage more widespread?     

Theoretically, controlling lift and duration does have advantages.
Practically, such advantages, even those for simple phasing, have
been difficult to achieve in production and on-vehicle.  When cost
is factored in, it's even harder to show a benefit.  Add the 
diagnostic requirements (OBD-II) for all the electric/electronic
components added and the practical application of a steady-state,
engine dyno-demonstrated benefit don't appear as great.


Anthony Tsakiris

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The opinions expressed are my own and not necessarily those of my employer.