Regarding the flame front propagation issue, note that I said that in the ABSENCE or DETONATION there is no significant difference in flame front speed and your information does not dispute this. Detonation is "abnormal combustion" and is a whole other ball game than normal combustion, which is detonation free. If you can use regular unleaded without signficant detonation as I can in my 2.6, then there is no difference in normal combustion flame front propagation speed. You have to differentiate between normal (no detonation) and abnormal (detonation) combustion. Generalities such as "premium gas burns slower" does not capture this critical distinction!

If your engine detonates consistently on a given fuel octane, you better increase the octane in short order before you cause permanent damage. Brief transient detonatation, such as what might occur if you short shift, will not cause any harm, and can usually be avoided by changing your driving habits - like shifting at higher revs and easing into the throttle.

On the vacuum advance issue. I have not actually tried to block the vacuum line to my EZL module, but I will probably try it when I bring the 2.6 out of summer storage for use this winter. It's due for an emission test in February. It appears that the vacuum line to the EZL is an input to igntion timing. Why else would it be there? I'll report on the results of my experiments and my emission test results.

Like your M103s, mine is on the ragged edge of the HC limit at 15 MPH. My theory is that the catayst bed cools off after several minutes of idling, which reduces oxidation efficiency, and this shows up as high HC and (relatively) high 02 on the 15 MPH test. The load during this test causes the converter to heat up and the HC and O2 go down due to higher catalyst oxidation efficiency; 0.5 percent O2 is very high and inidicates poor catalyst performance - probably due to low temperature. Good converter action should result in no more than 0.1, maybe 0.2 percent, O2. If the O2 level is zero, the converter is operating at "100 percent efficiency" using all the available O2, and at this point no further reduction in measured emissions is possible. My other theory is that 02 sensors may "drift" in their calibration, but I have not been able to confirm this. Reports I have read indicate that O2 sensor degradation results in increased response time, but this too could cause higher emissions.

If you have an IR gun run the following experiement. After 20 minutes of normal driving check the converter inlet temperature with the IR gun. Then let the engine idle and check temp. every minute. It will probably go down significantly within five minutes, which would indicate that the catalyst bed is also seeing a signficant reduction in temperature, which will reduce its oxidation efficiency and increase HC and CO.

Duke