Posting this here because while I typed this out, the orignal thread went off track in a bad way and the mods locked it.
In a venturi, the velocity is amplified.
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.
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.
Correct
Sort of, indirectly. It has less density so less O2 molecules per volume. Less O2 per volume consumed means less available for burning.
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.
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.
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.
Did he mean that as it sounds, or just as part of the reason sometimes jetting on race carbs needs to be adjusted for air.
