ISF Slower in hot weather - heat soak?
#16
Lexus Test Driver
It's an air density/oxygen capacity issue much more than it is a motor temperature issue. For the same reason cars loose power at high altitude even when the air is cool.
this is the same reasons that dynos compensate for ambient air temp and altitude when calculating HP.
Air Density Calculations:
To begin to understand the calculation of air density, consider the ideal gas law:
(1) P*V = n*R*T
where: P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature
Density is simply the number of molecules of the ideal gas in a certain volume, in this case a molar volume, which may be mathematically expressed as:
(2) D = n / V
where: D = density
n = number of molecules
V = volume
Then, by combining the previous two equations, the expression for the density becomes:
(3)
where: D = density, kg/m3
P = pressure, Pascals ( multiply mb by 100 to get Pascals)
R = gas constant , J/(kg*degK) = 287.05 for dry air
T = temperature, deg K = deg C + 273.15
As an example, using the ISA standard sea level conditions of P = 101325 Pa and T = 15 deg C, the air density at sea level, may be calculated as:
D = (101325) / (287.05 * (15 + 273.15)) = 1.2250 kg/m3
this is the same reasons that dynos compensate for ambient air temp and altitude when calculating HP.
Air Density Calculations:
To begin to understand the calculation of air density, consider the ideal gas law:
(1) P*V = n*R*T
where: P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature
Density is simply the number of molecules of the ideal gas in a certain volume, in this case a molar volume, which may be mathematically expressed as:
(2) D = n / V
where: D = density
n = number of molecules
V = volume
Then, by combining the previous two equations, the expression for the density becomes:
(3)
where: D = density, kg/m3
P = pressure, Pascals ( multiply mb by 100 to get Pascals)
R = gas constant , J/(kg*degK) = 287.05 for dry air
T = temperature, deg K = deg C + 273.15
As an example, using the ISA standard sea level conditions of P = 101325 Pa and T = 15 deg C, the air density at sea level, may be calculated as:
D = (101325) / (287.05 * (15 + 273.15)) = 1.2250 kg/m3
#18
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