Injector Math

[Gary Derian]

I don't know the exact timing specs.  What works best depends on the extent
of the intake/exhaust tuning.  A highly tuned system on both ends would
benefit the most by lots of overlap.  Without variable timing, the settings
are a compromise.  I would expect that knowing variable timing is available,
the idle setting would have less overlap than the standard setting and the
mid rpm setting would have more.  I was referring to the European spec BMW
M3 engine.  It is a 3.2 liter (200 cubic inches) L6 with 321 hp at 6800 rpm
and 253 lb-ft torque with a very broad torque curve.  This is net power!  Of
course, its a pretty expensive engine, 6 throttles, bundle of snakes 6 into
2 exhaust, etc.  Boosted engines have plenty of torque without the extra
complication of variable timing.  Jaguar, for instance, uses variable cam
timing on its new 4.0 liter V-8 in the atmo version but does not use it on
the supercharged version.

Interestingly, Porsche ran into a noise problem during the development of
the 2.5 liter flat 6 used in the Boxster.  It seem that during the high
overlap, mid rpm range, the intake pulsations were so strong they were
causing vibration in the wall of the plenum chamber which radiated a
considerable amount of noise.  They added thickness to the plenum, which is
molded plastic, to stop the noise.

Gary Derian <gderian at oh.verio.com>
>
>
> 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.
>
>