what _IS_ a good cruise A:F ??

[Johnny]

Tom Cloud wrote:
> 
>... 2 excelent posts deleted...

There are a few factors that can lead to pre-iginition and detonation.
Hot spots in the combustion chamber, too much ignition advance, shitty
gas, too much compression, too lean a mixture combined with one of the
above... the list goes on. And of course it can be a combination of any
or all of the above too.

You need to nail down a table of limitations for your engine and operate
inside that table. Most of the time, you can start by using well known
limits for your engine that have been discovered by trial and error by
possibly hundreds of thousands of experimentors. Take a 350 chev for
example. If you want to run on swamp water, er, I mean pump gas, and you
have iron heads, you are looking at 9:1 compression and typically a max
total advance of about 38degrees. If you are within these lines and you
get detonation or pre-ignition, I would start to look at mixture, spark
plug heat range, cylinder head temp, etc. Of course there are always
more variables, the above is just an example for one engine type.

The best single device to tell you what's going on inside is an EGT
guage. That combined with measurements from everything else will give
you plenty enough clues as to what's going on.

As a side note, my Z-28 has an Accel HEI (yuck) on it with the
adjustable vacuum advance and I have several spring sets for setting the
curve. It took me quite a while to get the curve just right so it
wouldn't ping at about 3000 rpm while still maintaining the total
advance I needed up high. If you're rattling, your hurting the engine.
Take it from someone that's ventilated more than one piston trying to
get that last couple hp.

-j-