I can speak from experience and say that this method definately works, and works
well. Some cars may have a little problem if they have a set of dished pistons
(lower compression) - because the engine is less likely to ping. Make sure it
is hot when you do it. It will probably not set you to the "factory
specifications," but it will not be injurious to your car. I have used this
method on my MGB and on my volkswagen beetle motor. Typically though, instead
of changing gasoline, one advances until it pings, and then backs it off just
enough that it doesn't ping.
I prefer to go the oposite way, however. The Bently manual gives the
distributor's advance curve (or at least a table of numbers). I like to check
with a stroboscope and see that the advance is proper when all the advance is in
- something I learned from my porsche (which has a factory procedure of checking
the timing at 6000 rpm). On my '67 MGB that means the strobe reads 20° at
2200rpm (for dist 40897 - high commpression) or 24° at 4400 rpm (for dist 40916
- low compression) with the vacuum line off.
Charles Sorkin wrote:
> A mechanic friend recently suggested the following method for setting timing
> on an older engine such as the A-series:
>
> 1. Let the gas tank get near empty, then add a gallon or so of an economy
> grade fuel.
> 2. Set the timing as far advanced as it will go until it starts pinging
> while under load.
> 3. Then fill the tank up with premium fuel.
>
> He claims that with a high octane fuel, it won't ping as early, and thus
> should provide peppy performance.
>
> I regarded this with skepticism, of course, but this fellow has been a
> mechanic for many years, and has set up more than a few racing engines. Is
> this a reasonable method? Or will I still be "detonating" the mixture?
>
> Regards,
>
> Charles
> '74 Midget
> '68 Sprite
> Bloomfield, NJ
> cdsorkin@ix.netcom.com
> "How about we duck inside for a Hen?"
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