I've heard tons of advice on AF ratios and ideal operating tempatures but no one has bothered to mention whether their engine is spark limited or mixture limited.

At NASA they have a saying:

"One test is worth a thousand expert opinions"

 

Apropos of nothing?

 

You lost me.

 

What's this in regard to? What do you mean by "spark limited" or "mixture limited"?

 

The definition of a "spark limited engine" is an engine in which increasing the timing will increase the torque up to the threshold of pinging. This is very common on stock engines or modified ones with plenty of compression.

In a mixture limited engine (modified engines that don't have enough compression or stock engines manufactured in the mid to late seventies) maximum torque is attained at say 36 or 44 or whatever but the engine doesn't ping until some higher number say 50 which yields less torque. So if you have the timing set for maximum torque the only way you can get the motor to ping is to lean out the mixture. Here again, this would definatively tell you the motor doesn't have enough compression. A text book example of such a motor would be a second generation F body car like a 78 or so with a 192 degree cam and 8:1 compression. Believe it or not spark limited and mixture limited are actual engineering terms.

This is relative because the spark limited engine will produce the best power with a 160 degree thermostat and mixture limited engine would put out more power with a hotter thermostat (in order to raise cylinder pressure).