So while we are on this subject, how much timing is too much under idle/light load conditions? I was surprised at the temp drop I got once I built an advance curve into my ECU. I haven't tried it over 45 yet. I figured with a 4500 converter and the timing returning to 35* under any appreciable load(and above 3500RPM) I am safe from a spark knock standpoint.
Using the old school method :)-hook up a vacuum gauge to the intake manifold. Set your idle speed rpm. Then start advancing the timing while maintaining the same idle speed rpm. When you see the vacuum reading start to fall off, back the timing down a couple of degrees and you are there. As far as total timing ( mechanical and vacuum )at cruise, depends on a lot of factors, including the DA, but generally speaking, most vacuum advance units come with about 16* built in them. Soooo, if you are cruising around 3K and your total mechanical is 36* and it's all in at 2800rpm, 36* plus 16* would give you a total timing at cruise of 52*. Very common #'s for your average warmed up street machine. Adjustable vacuum advance units are available for most distributors and they are the way to go. I used to adjust my cruise timing ( with adjustable vacuum pot )by slightly dipping in to the throttle while at cruise. If I could hear a little "tinkling", I would back off the vacuum pot a few degrees - until the noise went away.
