Once the best initial and mechanical advance has been determined and set, one method of testing and calibrating a distributor for optimum vacuum advance at cruise, with a carburetor equipped engine, is to use a good vacuum gauge and a vacuum pump. One connects the vacuum gauge to the manifold port on the carburetor and runs the hose into the cabin so it can be read while the car is being driven on the test section of highway. Next a vacuum pump, with an accurate gauge attached, is connected to the distributor vacuum advance can and that hose is also run into the cabin. A driver and a recorder is needed, along with a five to ten mile stretch of flat highway.
The car is driven at the desired cruise speed, 50, 60, 70 MPH whatever the owner determines the car would normally cruise at. The recorder then slowly activates the vacuum pump until the vacuum advance is activated and the car starts to speed up. The manifold vacuum and the reading of the gauge on the pump is recorded. To keep the car at the test speed the throttle will have to be closed somewhat which in turn will result in a higher manifold vacuum. Once the test speed is re-established the recorder adds an inch of vacuum to the pump, the driver keeps the car at the test speed and the manifold vacuum is recorded. The pump and manifold vacuum is recorded for every step applied to the advance with the pump. As the advance builds the throttle is closed more resulting in more vacuum and less fuel air charge going through the carburetor, resulting in a more economical cruise, all the while maintaining the desired test speed. After the maximum manifold vacuum is reached the car is taken back to the garage and with the use of a timing light and the vacuum pump the actual timing numbers are recorded for every point of vacuum that was supplied by the pump during the test.
The vacuum advance can then be calibrated to give the amount of advance that was obtained which resulted in the highest manifold vacuum at the test rpm.
That test would take almost no time if one had a way to adjust the timing while driving like Firebob does with his fuel injection system. One could also adjust the timing on the fly to a point that gives the best air/fuel ratio if an A/F gauge was installed in the car.
Do those Sniper systems even have a throttle blade or is it port injected?