All else being equal engine power varies directly with the air pressure, ie high barometer = higher power output.
Here at high altitude it is common for our outside air pressure to be 23.41 inHg, (about 11.5 psi) so our power output for NA engines is down to about 78% of normal.
Air pressure is good --- Like Richard says it would be good to race in a South African Gold mine except for the high temps.
Larry