Altitude compensation

[robert dingli]

Bryan wrote,

> Isn't it true that for a speed density efi system with an _absolute_ MAP 
> sensor, then altitude compensation is not needed?  For example, if you 
> changed altitude, the barometric pressure changes, which changes the 
> pressure in the manifold, which the MAP sensor directly measures. 
>  Temperature (air density) compensation is still needed.

This is correct to a certain extent.  There is still the backpressure
on the exhaust which makes a small difference.  I have never come across
an aftermarket efi which takes this into account.

OEM speed-density controllers such as the Ford EECIV/V on the 6 cylinder
Falcon do mesure barometric pressure (using the same sensor during prior to
starting) and compensate.

> Now for a efi system using the "trap door" air flow meter, I believe 
> altitude compensation is needed.  In addition to temperature  compensation.

Indeed.

Robert
-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **