    
Bob UK
Unregistered guest
Posted From: 94.197.122.87
| | Posted on Friday, 02 January, 2015 - 11:05 am: |    |
Recently a posting about setting the timing by advancing until it pinks and backing off.
I was looking for Lucas ignition coil specifications and I found dizzy doctor and they make a big fuss about calibration of the centrifugal advance, it's nonsense.
It may surprise some that no matter how the engine is timed its never actually correct.
The reason is that the centrifugal advance senses rpm not load.
So what may be correct at 2000rpm on a light throttle is different from 2000rpm on full throttle.
The centrifugal advance can't tell the difference.
So as long as the centrifugal advance is roughly right and not fully advanced at idle and has full range then the best one can do is make sure it doesn't pink.
The vacuum advance only works on small throttle openings.
On race engines with centrifugal advance often the ignition is fully advanced by 1000rpm. So after that the timing is fixed. They don't care about the advance as long as its retarded enough for the engine not to kick back on the starter.
On light throttle the engine is sucking in less air and fuel which takes longer to burn so more advance.
On full throttle more air and fuel burns quicker so less advance.
Engine designers set the ignition up to the worse case which is full throttle.
Max advance for any petrol engine is between 30 and 35 degrees.
The RR dizzy is about 26 centrifugal plus 5 baseline setting making 31 deg.
A lot of Lucas equipped cars are the same.
Bob UK
(Message approved by david_gore) |