"Negative Overlap" or more commonly known as Pressure Balance cams

[Tom Sharpe]

EFISYSTEMS at aol.com wrote:

> Hi All,
>        There are lots of great theory's out there regarding camshafts....and
> one of them is to have negative overlap and open the intake valve after tdc,
> while this sounds good in theory it doesn't generally work dynamically or
> mechanically.....I don't want to go on forever with this so I will just
> address a couple key points.....In theory it would be great to open the intake
> valve after tdc.......if we could SLAM it open with no delay AND have the
> air/fuel immediatly start filling the cylinder,,,,but such is not the case in
> any engine....the valve gradually opens and doesn't reach peak lift till over
> 100 degrees atdc...

A quick point about 302 fords 454 chevys and other "short" rod motors. their camshafts
are designed to open the intake as quickly as possible because the short rod tends to
"yank" the piston away from TDC and "yank" the air column to get it moving.... which
is really hard to do with the valve half open!!!  sharpe