RE: Smog tests

[White Anthony <anthony.white@xxxxxxxxxxxxxx>]

> My '73 has the valve timing adjusted with a bit more overlap than stock.
> Under high loads and RPM, that can make it pull unburned charge through
> the exhaust right?  Could the opposite effect be obtained going the
> other way?  

The answer is yes, but the reasons are backwards.  

The point of increased valve overlap is that the extra air/fuel mixture is drawn into the cylinder at high rpm, and then burnt in the cylinder, providing greater power.  The downside of this is that unburnt charge is pumped out through the exhaust at low rpm, giving high levels of unburnt hydrocarbons.  

To decrease unburnt hydrocarbons at lower rpms, the valve overlap can be decreased, as you suggested.  This is basically what the early Alfa VVT did, retarding the intake cam, and so decreasing the valve overlap at  engine speeds under 1800 (?) rpm.  

Regards,
Anthony.  
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