> I recently found a source that had a good suggestion. Instead of
> setting the
> timing at idle the way we usually do, set it when the centrifugal
> advance and
> vacuum advance are maxed out! Then set the timing close to the MAXIMUM
> desired advance. 30 degrees for the 4 cylinder cars would be a
> decent point,
> there probably would be room for more advance to be added by the driving
> technique.
Just a side comment to this ... "maximum advance" is usually given in
full-throttle terms (since that's when knock is most likely to occur, and
also when correct advance is most important), which means NO vacuum advance.
> Then observe the advance at idle. There should be 15+ degrees
> less advance at
> idle. If not, then one of your advances is not working correctly.
Specs vary for different engines, but generally the centrifugal advance
alone can contribute 15+ degrees.
I've only got TR2 specs handy, they call for a total of 13-15 degrees
centrifugal advance (@ 2700 rpm) and 6-8 degrees of vacuum advance (@ 18" of
mercury vacuum). These numbers definitely vary for later engines (which is
why there were so many different distributor part numbers).
Of course, the 'correct' advance curves are set by a lot of variables, many
of which are no longer the same as they were in 1954. Today's fuel in
particular is far different, plus by now most people have oversized liners
and whatnot. Even improved oils result in less oil contamination, which can
affect optimum spark advance.
I believe Kastner's Comp Prep manuals suggest modified curves, to match the
engine mods he suggests.
In addition to checking both full and no advance for both advance
mechanisms, I believe you should also check that the centrifugal mechanism
works smoothly. This procedure is on page M19 of the TR2-3 factory workshop
manual.
I also believe that rather than being a slave to a strobe light, the most
important thing is that the engine never knocks under operating conditions.
Therefore, I always set my timing "by the book" ... the road test method.
After finding the point where the engine will just barely knock when lugged
down, I like to back off a degree or two, to be sure it never knocks. I use
the strobe to check advance operation at each tune-up, but fine-tune the
advance on the road.
Randall
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