Remember too to consider air density as part of the equation, as the gasser is air throttled.
For a good primer on air density read
this:
http://www.bankspower.com/tech_howairflows.cfm
And this:
http://www.bankspower.com/Tech_SecrettoMakingPower.cfm
And this:
http://www.bankspower.com/Tech_firstair-thenfuel.cfm
There is more reading at other sites, but that is a good start.
Behemoth60 made mention and linked to an interactive site a while back, however I have not had time to put my mind to it...
hth's
gb