> For example, years ago I remember noting with one
> of my Fiats that when a shop had set the timing incorrectly the
> result was a change in how the engine sounded (besides the
> traditional "pinking").
Can't really comment, except to say I've never noticed a change in exhaust
note because of ignition timing except when it's really late, meaning it
takes more throttle to hold speed.
> A related question is whether earlier timing would be expected to
> give a cleaner exhaust. My thoughts say yes because longer burn
> times mean less hydrocarbons.
I'm certainly no expert, but it's my belief that burn time is not an issue.
Once the mixture is properly lit, it will keep burning even if the exhaust
valve opens. And it normally burns very fast, so a 10% change in timing
just won't make any measurable difference in HC.
However, late timing does reduce NOx production, by lowering peak combustion
temperatures. NOx is formed any time air is heated hot enough, so lower
temps mean less NOx. Also means lower engine efficiency, which means less
power ...
And, ISTR high NOx is one of the symptoms of (possibly inaudible)
detonation.
> The reason for the questions is that I'm still trying to settle on
> the optimal ignition timing for the GT6. I hear no obvious pinking
> (amidst all the other racket the car makes!). Don't really know if
> the cams are stock. I've been keeping it when idling at about 4 deg
> earlier than the designated static timing, but cognitively that seems
> early.
Might be OK, especially if it's a 'smog' engine as even their static timing
was deliberately late (for the above reason). You could try checking fuel
mileage, and of course keep an eye on the plugs for any detonation damage,
but otherwise it's probably OK.
> Given the carbs it has (a pair of H4S's), I (believe I) can't
> easily hook up the idle retard and set it to spec
The question really isn't the model of carbs, but rather whether they have
the proper vacuum port for the retard. It's usually possible to add a port,
if you really want to.
Personally, given the price of petrol these days, I'd be looking at
converting to a vacuum advance instead.
(And please, no lectures ... I'm quite well aware we pay less for (and use
more) fuel here than anywhere else in the world. Still doesn't hurt to try
to conserve it now, does it ?)
Randall
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