Injector Math

[Walter Sherwin]

>Negative overlap cams are what you might expect.  The intake valve opens
>after the exhaust valve closes.  This design greatly reduces the mid range
>torque of an engine in exchange for fewer concerns with EFI tuning.  The
>really high output atmo engines have variable valve timing to greatly
>increase overlap at mid rpm.  During idle and high rpm overlap is reduced.
>At idle, high overlap causes great reversion and poor emissions.  At high
>rpm, exhaust backpressure limits the effectiveness of overlap.  Also at
high
>rpm reducing overlap retards the inlet valve closing which helps cylinder
>fill.




Thank-you Gary!  One question though.  I kinda figured that the "negative
overlap" cam title referred to reduced overlap, during the period which both
the intake and exhaust valves would be simultaneously off their seats, near
TDC.   Did the "n.o." cams go to the extreme of actual "zero", or
"negative",  seat-seat overlap?  Or,  just significantly reduced overlap
versus their naturally aspirated counterparts?

Thanks;
Walt.