[Healeys] Cam Timing

[Dave & M]

Hi Dave,

Do be sure to check all cam lobes for specified lift to make sure that
one or more cam lobes are not worn. This can happen more easily than
you would suspect.

Your numbers do indeed indicate that the cam is timed for maximum
intake lift at four degrees earlier than the BJ8 spec. The really
important number is the point at which the intake valve closes ABDC
when the piston is on it's way back up. Advanced timing will also
cause the intake valve to close sooner. Since at LOWER to mid rpm the
piston rising will push part of the intake charge back out past the
still open intake valve, earlier intake closing (advanced timing) will
let less charge be pushed back out, give more cylinder pressure & power.

At some HIGHER rpm where charge column inertia is high enough to keep the
cylinder still filling despite the piston rising, there will be
relatively more cylinder filling & more power. The exact dynamics of
this will depend on the exact engine configuration.  In general,
advanced cam timing will produce more low rpm torque & less high rpm
torque.  Retarded cam timing - the opposite.

I think four degrees would certainly be enough to be noticeable. There
are various ways to make minor cam timing adjustments. Perhaps one of
the easiest is to use an offset cam key.

Regards,
Dave Russell




David Masucci wrote:

 > So I'm pretty confident that my number one intake hits maximum lift
 >
at around
 > 106 ATDC.
 >
 > I understand that the spec for the BJ8 is 110 ATDC for this
parameter. It
 > appears that my stock BJ8 cam is about 4 degrees advanced from
 > where
it should
 > be. What can I expect from this error? Could 4 be enough to produce
 >
a fall
 > off of higher RPM power? I thought advancing the cam timing would
give the
 > opposite effect? Any thoughts?? Does this make sense?
 >
 > Dave BJ8