I have been using the engine pick up for my primary speedometer for about 10 years. It reads and calibrates a little different from the boat mounted pickups because it sets deeper in the water. One of the advantages of the Airguide speedometers is that they can be calibrated for changes in air pressure. Since the engine mounted pick up sets deeper in the water than the airguide pickup it reads a little higher at rest. It is actually reading the static pressure of the water at that depth. Once the speedometer is properly calibrated on a given day you can note the reading at rest. I think mine reads around 5 at rest. All you have to do is set the speedometer at that reading at the beginning of the day providing you have the same load in the boat. The major advantage of the engine pickup is that it is way less prone to becoming clogged and it is less susceptible to turns and other disturbances. My speedometer that is hooked up to the pickups is only a back up and I am considering running both speedos off of the engine pick up. The differences in speed readings are only noticeable at low speeds. The Airguide was designed as a water ski speedometer, and to be accurate at low speed. jim
Was on line the other day and cam across this site. (Speed-o-Clear) Looks similar to the old system that was out there years ago that used a can of compressed air and a 12 volt air solenoid. This system looks like it uses a small air compressor. I "E" mailed them asking if they would work with dual speedos and the reply was one might not have enough power to push the clog out if "T"'d in so you should purchase two. (Price is $59.99 plus ship/handl each.) The pump in the picture looks like a aquarium unit, only 12 volt. Don't know if that would build up enough initial pressure to push a clog. Bob
