Effect of Air Density on Carburation
Posting this here because while I typed this out, the orignal thread went off track in a bad way and the mods locked it.
We actually pull in the same volume of air in Colorado as they would in Florida - the air just has less density.
Correct
air has less energy in it
Sort of, indirectly. It has less density so less O2 molecules per volume. Less O2 per volume consumed means less available for burning.
Thinner air passing through the venturis has less vacuum than denser air.
The depression is most dependent on velocity. In a simple pitot tube a change in velocity goes up by the square over 2, where the change in density effects the pressure just by 1/2.
In a venturi, the velocity is amplified.
only compounds the issue of poor signal at the boosters
Poorer but not poor. Within the parameters we're discussing, once boosters are delivering fuel, the signal is quite strong.
Bottom line is density is important to the main system but not significant enough to require recalibration of jetting in a street carb. The effect of the lower air density will be matched with a reduction in fuel delivered.
This is why you can race to the top of Pike's Peak with a carburated vehicle without making changes along the way.
This means the problem of an oversized carb will only be compounded at our altitude.
Compounded might be a little strong phrase, but yes, it will be worse. Probably the bigger effect caused by reduction in signal will be it will have to run on the idle system to higher rpms.
In the later emissions era you can find examples of carburetors with additional features for altitude compensation. And even those, when sold/serviced for high altitude had slightly different calibrations. The ones I'm thinking of are 2bbl Motorcrafts. Would have to look and see if it was neccessary on the 4 bbl versions of the same, or on any of the very late production OEM Q-jets and Holleys 4 bbls. Might not have been.
