Injection Pump High Altitude Compensator
 

Do high altitude compensators on a D24 NA injection pump show any real benefit at higher elevation or are they more trouble than they are worth?

Having lived at both sea level and higher elevations I can say I don't notice any meaningful benefit from the altitude compensation system. My 1986 745 has it and my 1983 764 doesn't. Both run fine both at low and high altitudes. In fact I disabled the high altitude compensation system on the 745. I would rather set the static timing to accommodate the altitude since the compensator system is pretty crude anyway (only has two steps for hi/lo elevation which is a far from accurate solution, rather than infinite adjustment like a modern engine management system would use) and furthermore is vulnerable to common failure of the barometric pressure switch that senses the altitude and controls the system.

One problem with the system is that its "failure mode" results in the altitude compensation (timing advance) being constantly ENGAGED, not disengaged. Thus if something breaks or gets unplugged, you could end up unknowingly running excessive advance at low elevation, putting the engine at risk of damage from overly high combustion chamber pressures. That is a far more serious concern than the opposite situation of NOT having the advance at high altitude, which would merely result in slightly reduced power and efficiency.

Not worth the effort IMO, especially if most of your driving is done at relatively low elevations. Remember that the altitude compensation system ---- IF (and this is a big if!) it is operating correctly ---- only engages above about 3300' elevation IIRC. If you are based in NY, then I think you would need to drive a long ways west to find that kind of altitude anyway, no?