GK
03-21-2001, 01:50 PM
Great To Know Formulas
Brake Specific Fuel Consumption (BSFC)
BSFC = LBS of fuel per hour / horsepower
(generalized as: 0.45=lean, 0.50=normally asperated,0.55=supercharged/nitrous oxide)
To figure injector size:
HP = horsepower
NC = number of cylinders
Injector Size = (HPxBSFC)/NC
example:
300x0.50/8 = 18.75 or 19lb injectors
Duty Cycle = (DC)
DC = Safe Injector Duty Cycle
(Injectors are rated at 100% flow compacity, expressed 100% of their Duty Cycle. We need to adjust the number for the percentage of time the injector must be shut down between pulses to avoid damage. Running an injector at a flow rate of more than 85% of its Duty Cycle will damage the injector, in practice the injector should not be run at greater it's Duty Cycle in continuous mode.)
------------------------------------------------------------------
To Figure The Maximum HP an Injector Can Sustain:
Max HP = (NC x injector size x DC)/ BSFC
example:
8 x 19 x 80%(or 0.80) / 0.50 = 243.3HP
------------------------------------------------------------------
CFM
To find correct carburetor CFM for an engine:
cfm = C.I.D. x 2 = cfm
This theory works well for street applications but race engines applications are not always correct.
------------------------------------------------------------------
Figuring MPH
MPH = tire radius / 168 x engine rpm /gear ratio
------------------------------------------------------------------
Figuring RPM
RPM = 168 x gear ratio x MPH / tire radius
------------------------------------------------------------------
Figuring gear ratio
gear ratio = tire radius x RPM / 168 / MPH
------------------------------------------------------------------
Figuring tire radius
tire radius = 168 x MPH x gear ratio / RPM
Thanks to Phantom Z
Brake Specific Fuel Consumption (BSFC)
BSFC = LBS of fuel per hour / horsepower
(generalized as: 0.45=lean, 0.50=normally asperated,0.55=supercharged/nitrous oxide)
To figure injector size:
HP = horsepower
NC = number of cylinders
Injector Size = (HPxBSFC)/NC
example:
300x0.50/8 = 18.75 or 19lb injectors
Duty Cycle = (DC)
DC = Safe Injector Duty Cycle
(Injectors are rated at 100% flow compacity, expressed 100% of their Duty Cycle. We need to adjust the number for the percentage of time the injector must be shut down between pulses to avoid damage. Running an injector at a flow rate of more than 85% of its Duty Cycle will damage the injector, in practice the injector should not be run at greater it's Duty Cycle in continuous mode.)
------------------------------------------------------------------
To Figure The Maximum HP an Injector Can Sustain:
Max HP = (NC x injector size x DC)/ BSFC
example:
8 x 19 x 80%(or 0.80) / 0.50 = 243.3HP
------------------------------------------------------------------
CFM
To find correct carburetor CFM for an engine:
cfm = C.I.D. x 2 = cfm
This theory works well for street applications but race engines applications are not always correct.
------------------------------------------------------------------
Figuring MPH
MPH = tire radius / 168 x engine rpm /gear ratio
------------------------------------------------------------------
Figuring RPM
RPM = 168 x gear ratio x MPH / tire radius
------------------------------------------------------------------
Figuring gear ratio
gear ratio = tire radius x RPM / 168 / MPH
------------------------------------------------------------------
Figuring tire radius
tire radius = 168 x MPH x gear ratio / RPM
Thanks to Phantom Z