Now that I mentioned the Important People, I will pass along a group of Formulas that every Engineer or Technician who took our class: "Engine Power Boosting" received in the hand-out. The Information was put together by a Technical Specialist named Mike Briggs.
All of the Formulas posted below came from Charles Fayette Taylor in his book:
"The Internal-Combustion Engine in Theory and Practice, Vol. 1"
Taylor Vol.1 (1-2) Formula #1 w=JQ
w= work done by the system minus work done on the system
Q= is the heat added minus the heat rejected by the system
J= a "Units Constant" 778 ft.lbs/BTU in English Units.
Taylor Vol.1 (1-4) η=P/JMfQc
η= efficiency
P= power
Mf= mass of fuel supplied per unit time
Qc= heat of combustion of a unit mass of fuel
Taylor Vol.1 (1-5) P=JMafQcη
Ma= Mass of air supplied per unit time
F= is ther mass ratio or fuel to air
Taylor Vol.1 (1-6) sfc=Mf/P
sfc= specific fuel consumption 9lbs./(BHP-hr) for English units)
Taylor Vol.1 (1-7) sac=Ma/P
sac= specific air consumption is air consumed per unit work
Taylor Vol.1 (6-2) for a 4 stroke engine
ev= 2Mi/(NVdρi
ev= volumetric efficiency (also uses ηvol)
Mi= mass of fresh mixture per unit time
N= number of revolutions per unit time
Vd= total displacement volume of the engine
ρi= inlet density
Some formulas assume Volumetric Efficiency to be 100%
Most "back of the envelope" calculations (which we are posting here) should assume
80% volumetric efficiency.
The previous formulas are used to calculate airflow for a naturally aspirated engine.
But we are talking about a BOOSTED ENGINE in this topic so:
1) You want to target numbers for Horsepower and Torque at given engine rpm points.
2) There are programs out there (like the Wallace Racing calculators) to predict for a given engine what the Volumetric Air Flow Rate and Related Pressure Ratio would be.
For the Turbo stuff you would use Borg Warner's "Matchbot"
www.turbos.bwauto.com/aftermarket/matchbot.aspx
The program is not that difficult to learn how to use and gets you in the ballpark for your Engine goals vs the right Turbocharger Size.
That is all I want to post on the Theory of Boosting today.
Tom V.