The book figures always erred on the side of conservatism even when new to
take account of manufacturing tolerances and individual cars could often
benefit from slightly more advance than the book figure. 30-odd years down
the line, especially with different components to that originally, and
petrol nothing like it was then, the book figures are even less relevant
although they can be a useful starting point. The centrifugal and vacuum
curves are probably nowhere near the curves that would be ideal for your
engine now, possibly only touching in one place like a cheap suit :o)
Basically run it with as much advance as it can take without pinking at any
combination of revs throttle opening and load and that will take account of
all the variable of your engine. 10 degrees BTDC sounds about right, I
don't know where 2 degrees after comes from, once centrifugal and vacuum
advance come into play you get more advance, not less, and can be up to 50
degrees.
I don't know about the Midget but the MGB always used vacuum advance, and
this was irrespective of whether the vacuum source was the carb or the
manifold, despite what some may claim. The difference was only an emissions
frig and any system can be run with either. In fact when the UK engines
changed from carb to manifold vacuum they retained the same engine and
distributor. Generally performance is reckoned to better with pre-emissions
distributors and settings.
PaulH.
----- Original Message -----
From: "Rick Lindsay" <rick@stoolhead.com>
To: "mgs" <mgs@autox.team.net>
Sent: Tuesday, June 08, 2004 4:51 PM
Subject: Midget 1500 ignition timing
> Where am I going with this? I need is to design
> the 'best' static or low engine speed timing for
> general street use. The manuals vary between 10
> degrees BTDC to 2 degrees ATDC. These numbers
> represent both emissions-related settings AND the
> way the vacuum is ported to the distributor.
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