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March 8, 2007
Turbocharger Specs & Calcs
Turbonetics T04E
O Trim Turbine Wheel (appx 61.7 Trim)
EXDUCER DIA.: 2.296" (58.3mm)
MAJOR DIA.: 2.922" (74.2mm)
40 Trim Compressor Wheel
INDUCER DIA.: 1.870" (47.5mm)
MAJOR DIA.: 2.950" (74.9mm)
INLET DIA.: 3.000" (76.2mm)
OUTLET DIA.: 2.000" (50.8mm)
TrimCompressor = (Inducer Dia) ^2 / (Major Dia) ^2 * (100)
TrimTurbine = (Exducer Dia) ^2 / (Major Dia) ^2 * (100)
Larger trim supports more airflow
.58 A/R
Map:
To read the chart, first calculate the airflow.
Cubic Inch Displacement (CID) = 399
Volumetric Efficiency (VolE) = 90% (estimated)
RPM = 6000
Boost Pressure = 5 psig, 14.7 psig, 20 psig
CFM = RPM * CID * VolE / (1728 in^3 per ft * 2 revolutions per cycle)
CFM = 6000*399*.90/3456 = 623 cfm
Since the Turbonetics maps are in their corrected lb/min, we have to convert CFM to lb/min, and then apply a correction to match their inlet temperature & pressure.
Ideal Gas Law is PV=nRT, or switched around to lbs is n (lbs/min) = PV/(RT)
P is Absolute Pressure, psia, so add 14.7 to your boost pressure
5 + 14.7 = 19.7 psia
V is Volume, or CFM = 623 cfm
R=10.73 (universal gas constant for air in these calcs)
T=Temp, in Rankine (add 460 to DegF), 110 degF + 460 = 570 degR
19.7 psia * 623 cfm * 29 / (10.73 * 570 degR) = 58.2 lb/min
Since we have 2 turbos, also divide by two.
Lb/min@5psi = 29.1 lb/min
Lb/min@14.7psi = 86.8 / 2 = 43.4 lb/min
Pressure ratio = (boost + atmosphere) / atmosphere
PR5 = (5+14.7)/14.7 = 1.34
PR14.7 = 2
Draw a line from the lb/min on the X axis going up, and the pressure ratio on the Y axis going across. Where they intersect is the turbochargers efficiency (and speed). At 5 psi, you have a PR of 1.34, and 29.1 lb/min. This is to the lower right of the graph, and not very efficient (on the 69,800 rpm line). At 14.7 psi boost, you are at a PR of 2 and 43.4 lb/min, well to the right of the map. This shows that the engine is producing much more flow than the compressor can pump, so it won't be very efficient. Back when these turbos were chosen, they were designed around 5500 rpm 305 (436 cfm) and 8 psi boost (PR 1.55), which has 22.7 lb/min airflow, and would be right around 72% efficiency. Upgrading to a 60 Trim compressor would put me at 70% at 5 psi, and 73% at 14.7 psi boost.
What I need to do for now is short shift it. By reducing the RPM by a third to 4000, the airflow also gets cut by a third. 5psi=19.5 lb/min & 65% efficiency and 14.7psi=29 lb/min & 73% efficiency.
Posted by Z28tt at March 8, 2007 5:29 PM