Shorting the R16/1 resistor reduces the rate of spark advance with revs, but I believe full advance (IIRC 32 degrees) is achieved at 3200 regardless of resistor value including zero.

Your test speeds were just under 1800, so the advance due to revs with the resistor shorted is less than with the OE 750 Ohm resistor.

Plugging the vacuum advance signal line to the EZL will further retard spark advance at the test speeds and loads, and the more you can retard spark advance at the test speeds and loads the lower the peak combustion temperature, which reduces engine out NOx, and the greater the EGT increase to kept the catalyst hot enough to maximize oxidation and reduction reactions.

I don't know the effect of doing only one of the above because I have never tested those conditions and it's so easy to make the temporary modifications that I do both.

There is no effect on initial timing because it is fixed by the EZL and is not adjustable, which is written on the emission control data sticker. Because of this the tech is NOT required to check initial timing. This is stated in the emission test manual that you can download from the BAR Web site.

Most of the time when I inform the tech that they don't need to check initial timing because it is fixed they just sarcastically reply:"We check them all". Most of these guys are jerks who think I'm just another dumb consumer. I very likely know more about emission control than they do.

Back in the late sixties I did a MSME at the U. of Wisconsin Engine Research Center and did emission related research on a GM fellowship. Back then we pretty much knew how emissions were created and how to control them, but we didn't have the engine management technology with sufficient granularity to control fuel flow and spark advance to the necessary very tight tolerances under all operating conditions, and it took a decade or so to get there.

Microprocessor controlled port EFI and spark advance and development of the O2 sensor and three-way catalyst that oxidizes HC and CO2 and reduces NOx got us over the hump.


Duke