Injector Math

[Gary Derian]

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.

Gary Derian <gderian at oh.verio.com>

as to the bumpstick itself, i'd suggest asking about a "negative overlap"
cam.  the cam grinder you want to do biz with will know what this
is and how to tailor it to your situation.  the minor added expense of
getting a true custom cam will be more than offset by the results.
IIRC, the latest tt porsche awd turbo used a neg overlap cam.


Hi.  I'd like to know more about these "negative overlap cams".  Seriously!
What are they, and how do they differ from the norm?  Ditto on your comments
about finding a cam grinder who will tailor YOUR cam to YOUR application.
Walt.