Hi Wayne,
Advancing the cam 8 degrees will usually actually boost low & mid rpm
power. The intake valve closing timing is actually the single most
important of the valve timing events. Since no compression of the
mixture can begin until the intake valve is closed, earlier closing
gives more compression & power.
Early closing of the intake works somewhat against you at the higher rpm
where intake inertia will actually overcome the rising piston & continue
cylinder filling for a bit. Obviously, sufficient inertia is not present
at lower rpm & the rising piston simply pushes some of the mixture back
out of the cylinder before the intake valve closes. Earlier intake
closing helps prevent this situation. The effect of advanced timing has
much less effect on the other valve timing events.
Competition engine cam timing is often adjusted to optomize the power
band for the track length & speeds.
I think you may be pleasently surprised about how much you will gain
with properly set up HD8's & the present cam timing. Unless of course,
you are after maximum high rpm power for top speed, which I doubt.
Regards,
Dave Russell
WAS wrote:
> I would like to thank everyone who for their input on the Healey with
> low power and DGV carburetors. The plan is to swap the DGV's for a pair
> of rebuilt HD-8 SU's and a two inch manifold used with the current
> header. We have decided to leave the cam advanced the 8 degrees for now.
> I like to do one thing at a time so carburetors first, and since
> the 8 degree advance is less then one tooth I will need off set keys or
> variable timing gears to correct the error. I wonder what the normal
> manufacturing variation in cam timing was when new. So we have decided
> to address this at a later date as money allows. I enjoyed everyones
> input and a lot of ideas were offered that I had not considered. I will
> update the group after we change the carburetors.
>
> Regards
> Wayne
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