Hi Folks,
I tell this to everyone who will listen, but few apparently do.
On high compression engines, it is important to set ignition timing at
an rpm where maximum static plus centrifugal advance (vacuum advance
not connected) is all of the way in. Depending on the particular
distributor, this could be anywhere from 4,000 to 5,000 rpm. Most
engines will tolerate between 32 & 36 degrees of total maximum
advance, depending on engine tune, fuel grade, & altitude. In other
words, set for maximum advance & let the idle advance fall where it may.
It seems that many folks still insist on setting advance at idle &
letting the maximum advance fall where it may. This method is not
precise. The distributor's initial centrifugal advance curve is very
steep (advances quickly) at low rpm. Only a small error in the rpm
that the advance is set at can make a very large error in the total
advance at high rpm.
Seat of the pants timing is never reliable. A few degrees of over
advance "may" give better throttle response & a bit more overall
power, But the risks are great.
------------------
Quote Michael Salter:
Detonation can be quite serious at highway speeds but completely inaudible
to the driver. You can buy knock sensors which will turn on a light when
detonation is occurring; might be a good investment.
------------------
Quote Bob Spidell:
"I'm not convinced that the fuels that are available today,
particularly in
CA I understand, are good enough to handle the amount of advance that the
original distributors can produce. "
-----------------
I agree completely with Michael & Bob.
Regards,
Dave Russell
BN2
Michael Salter wrote:
> Hi Ken,
>
> I would say, largely because of the way the pieces have broken off
> the top ring land, that there is little chance that that damage is
> attributable to anything but detonation. The other marks in the
> pistons are probably the result of the broken off pieces hammering
> around before they went out the exhaust port.
>
> There appears to be a cracked piece just hanging on in this
> picture.
> I have seen similar damage several times particularly on MGBs and
> would suggest that you check your distributor advance curve
> carefully both before and after you have the engine rebuilt.
>
> I'm not convinced that the fuels that are available today,
> particularly in CA I understand, are good enough to handle the
> amount of advance that the original distributors can produce.
>
> Detonation can be quite serious at highway speeds but completely
> inaudible to the driver. You can buy knock sensors which will turn
> on a light when detonation is occurring; might be a good
> investment.
>
> Michael Salter
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