2vz & 3vz Turbo Choices & the Math Behind It
10-26-05, 10:07 PM
#1
Lexus Champion
Thread Starter
2vz & 3vz Turbo Choices & the Math Behind It
Since I just did the 2vz-fe for someone, I'll just post the data I did earlier anyways.
Calculating what the engine needs & how to read a compressor map.
To plot the compressor operating point, first calculate airflow:
Wa = Airflowactual (lb/min)
HP = Horsepower Target (flywheel)
A/F = Air/Fuel Ratio
BSFC = Brake Specific Fuel Consumption (per hour) Divide by 60 to get min.
Calculate required manifold pressure required to meet the horsepower, or flow target:
MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
Wa = Airflowactual(lb/min)
R = Gas Constant = 639.6
Tm = Intake Manifold Temperature (degrees F)
VE = Volumetric Efficiency
N = Engine speed (RPM)
Vd = engine displacement (Cubic Inches, convert from liters to CI by multiplying by 61.02, ex. 2.0 liters * 61.02 = 122 CI)
MAPreq = psia (remember, this is absolute pressure. Subtract atmospheric pressure to get gauge pressure (aka boost).
We will assume that there is a 2 psi loss. So to determine the Compressor Discharge Pressure (P2c), 2 psi will be added to the manifold pressure calculated above.
P2c = Compressor Discharge Pressure (psia)
MAP = Manifold Absolute Pressure (psia)
ΔPloss = Pressure Loss Between the Compressor and the Manifold (psi)
We will need to subtract the 1 psi pressure loss from the ambient pressure to determine the Compressor Inlet Pressure (P1).)
P1c = Compressor Inlet Pressure (psia)
Pamb = Ambient Air pressure (psia)
ΔPloss = Pressure Loss due to Air Filter/Piping (psi)
Now we can calculate the Pressure Ratio IIc
Engine Volumetric Efficiency. Typical numbers for peak Volumetric Efficiency (VE) range in the 95%-99% for modern 4-valve heads, to 88% - 95% for 2-valve designs. If you have a torque curve for your engine, you can use this to estimate VE at various engine speeds. On a well-tuned engine, the VE will peak at the torque peak, and this number can be used to scale the VE at other engine speeds. A 4-valve engine will typically have higher VE over more of its rev range than a two-valve engine.
Intake Manifold Temperature. Compressors with higher efficiency give lower manifold temperatures. Manifold temperatures of intercooled setups are typically 100 - 130 degrees F, while non-intercooled values can reach from 175-300 degrees F.
Brake Specific Fuel Consumption (BSFC). BSFC describes the fuel flow rate required to generate each horsepower. General values of BSFC for turbocharged gasoline engines range from 0.50 to 0.60 and higher. The units of BSFC are lower BSFC means that the engine requires less fuel to generate a given horsepower. Race fuels and aggressive tuning are required to reach the low end of the BSFC range described above.
Calculating what the engine needs & how to read a compressor map.
To plot the compressor operating point, first calculate airflow:
Wa = Airflowactual (lb/min)
HP = Horsepower Target (flywheel)
A/F = Air/Fuel Ratio
BSFC = Brake Specific Fuel Consumption (per hour) Divide by 60 to get min.
Calculate required manifold pressure required to meet the horsepower, or flow target:
MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
Wa = Airflowactual(lb/min)
R = Gas Constant = 639.6
Tm = Intake Manifold Temperature (degrees F)
VE = Volumetric Efficiency
N = Engine speed (RPM)
Vd = engine displacement (Cubic Inches, convert from liters to CI by multiplying by 61.02, ex. 2.0 liters * 61.02 = 122 CI)
MAPreq = psia (remember, this is absolute pressure. Subtract atmospheric pressure to get gauge pressure (aka boost).
We will assume that there is a 2 psi loss. So to determine the Compressor Discharge Pressure (P2c), 2 psi will be added to the manifold pressure calculated above.
P2c = Compressor Discharge Pressure (psia)
MAP = Manifold Absolute Pressure (psia)
ΔPloss = Pressure Loss Between the Compressor and the Manifold (psi)
We will need to subtract the 1 psi pressure loss from the ambient pressure to determine the Compressor Inlet Pressure (P1).)
P1c = Compressor Inlet Pressure (psia)
Pamb = Ambient Air pressure (psia)
ΔPloss = Pressure Loss due to Air Filter/Piping (psi)
Now we can calculate the Pressure Ratio IIc
Engine Volumetric Efficiency. Typical numbers for peak Volumetric Efficiency (VE) range in the 95%-99% for modern 4-valve heads, to 88% - 95% for 2-valve designs. If you have a torque curve for your engine, you can use this to estimate VE at various engine speeds. On a well-tuned engine, the VE will peak at the torque peak, and this number can be used to scale the VE at other engine speeds. A 4-valve engine will typically have higher VE over more of its rev range than a two-valve engine.
Intake Manifold Temperature. Compressors with higher efficiency give lower manifold temperatures. Manifold temperatures of intercooled setups are typically 100 - 130 degrees F, while non-intercooled values can reach from 175-300 degrees F.
Brake Specific Fuel Consumption (BSFC). BSFC describes the fuel flow rate required to generate each horsepower. General values of BSFC for turbocharged gasoline engines range from 0.50 to 0.60 and higher. The units of BSFC are lower BSFC means that the engine requires less fuel to generate a given horsepower. Race fuels and aggressive tuning are required to reach the low end of the BSFC range described above.
10-26-05, 10:09 PM
#2
Lexus Champion
Thread Starter
All of this is done at the torque/VE peak @ 4800rpm.
P1c = 13.7 (14.7 psi @ sea level - 1psi intake restrictions)
2vz-fe
200bhp @ 12 A/F Ratio - BROWN
200*12*.01 =
WA = 24lb/m
24*639.6*600 = 9210240
/
95%*2400*152 = 346560
MAPreq = 26.57 psia
P2c = 28.57 psia
pIIc = 2.08
230bhp @ 12 A/F Ratio - GREEN
WA = 27.6lb/m
pIIc = 2.37
3vz-fe
280bhp @ 12 A/F ratio - RED
280*12.5*0.01=
WA = 33.6lb/m
33.6*639.6*600 = 12894336
/
95%*2400*181 = 412680
MAPreq = 31.24 psia
P2c = 33.54 psia
pIIc = 2.42
320bhp @ 12 A/F ratio - PINK
320*12*.01=
WA = 38.4 lb/m
38.4*639.6*600 = 14736384
/
95%*2400*181 = 412680
MAPreq = 35.7 psia
P2c = 37.7 psia
pIIc = 2.75
350bhp @ 12 A/F ratio - BLUE
350*12*0.01 =
WA = 42lb/m
42*639.6*600 = 16117920
/
95%*2400*181 = 412680
MAPreq = 39.05 psia
P2c = 41.05 psia
pIIc = 2.99 psia
P1c = 13.7 (14.7 psi @ sea level - 1psi intake restrictions)
2vz-fe
200bhp @ 12 A/F Ratio - BROWN
200*12*.01 =
WA = 24lb/m
24*639.6*600 = 9210240
/
95%*2400*152 = 346560
MAPreq = 26.57 psia
P2c = 28.57 psia
pIIc = 2.08
230bhp @ 12 A/F Ratio - GREEN
WA = 27.6lb/m
pIIc = 2.37
3vz-fe
280bhp @ 12 A/F ratio - RED
280*12.5*0.01=
WA = 33.6lb/m
33.6*639.6*600 = 12894336
/
95%*2400*181 = 412680
MAPreq = 31.24 psia
P2c = 33.54 psia
pIIc = 2.42
320bhp @ 12 A/F ratio - PINK
320*12*.01=
WA = 38.4 lb/m
38.4*639.6*600 = 14736384
/
95%*2400*181 = 412680
MAPreq = 35.7 psia
P2c = 37.7 psia
pIIc = 2.75
350bhp @ 12 A/F ratio - BLUE
350*12*0.01 =
WA = 42lb/m
42*639.6*600 = 16117920
/
95%*2400*181 = 412680
MAPreq = 39.05 psia
P2c = 41.05 psia
pIIc = 2.99 psia
10-26-05, 10:11 PM
#3
Lexus Champion
Thread Starter
Along the left hand side is IIc. Along the bottom is airflow.
The & curves are efficiency. The higher the efficiency, the cooler the charge.
Centering your power demand around peak efficiency is good if you plan to upgrade later on.
For a street turbo, it's not bad to run off the back of peak efficiency somewhat. It's most likely to be a smaller turbo that will spool faster & driveability will be better.
Bring oooooon the compressor maps!
Garrett/Air Research:
T3 Trim 45 - T3 Trim 50
- 
T3 Trim 60 - T3 Super 60
- 
The & curves are efficiency. The higher the efficiency, the cooler the charge.
Centering your power demand around peak efficiency is good if you plan to upgrade later on.
For a street turbo, it's not bad to run off the back of peak efficiency somewhat. It's most likely to be a smaller turbo that will spool faster & driveability will be better.
Bring oooooon the compressor maps!
Garrett/Air Research:
T3 Trim 45 - T3 Trim 50
- T3 Trim 60 - T3 Super 60
-
Last edited by Pheonix; 10-26-05 at 10:14 PM.
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