Dyno Testing Results (1 February 1999)

The top line is the torque curve in Newton-meters (the vertical scale on the right) as measured by the dyno at the wheels during acceleration. The next line is the engine horsepower curve in kilowatts (the vertical scale on the left), which is computed from the torque curve using the familiar equation horsepower = torque x RPM / 5252. The next two lines are the wheel horsepower and drivetrain loss, also in kilowatts. Note that the drivetrain loss is computed from torque as measured by the dyno at the wheels during deceleration in gear with the clutch in; the flywheel horsepower curve is the sum of the wheel horsepower curve and the drivetrain loss curve.

Then we have the lines of text. Can't read German? Neither can I, but Roger translated. Here's the scoop, complete with conversions into SAE units:

P-Norm is the peak horsepower corrected to European DIN standards. 266 kW = 362 DIN PS = 367 SAE HP (conversion factors are 1.36 and 1.014, respectively).

P-Mot is the peak horsepower uncorrected.

P-Rad is the peak horsepower at the wheels. 185 kW = 252 DIN PS = 255 SAE HP (conversion factors are 1.36 and 1.014, respectively)

P-Schlepp is the drivetrain loss at the peak horsepower RPM. 79.5 kW = 108.1 DIN PS = 109.6 SAE HP (roughly 30%)

Maximale Leistung is the speed and RPM at which the peak horsepower was achieved (in fourth gear), 205 kph and 5680 rpm, respectively.

Drehmoment is the peak torque. 480 Nm = 354 lb-ft (conversion factor is .7375)

Maximales Drehmoment is the speed and RPM at which the peak torque was achieved (in fourth gear), 187 kph and 5180 rpm, respectively (note that torque was almost as high at as low as 3000 RPM)

Maximale Geschwindigkeit is the maximum speed achieved during the run, 220 kph

Maximale Drehzahl is the maximum RPM achieved during the run, 6090 rpm

Luftdruck is the ambiant atmospheric pressure, 989 mbar (about 1.02 kg/cm2)

Ansaugdruck is the intake pressure (not measured)

Abgasdruck is the exhaust pressure (not measured)

Lufttemperatur is the ambiant air temperature, 9 degrees Celsius

Oltemperatur is the maximum oil temperature during the run, 91 degrees Celsius

Abgastemperature is the exhaust temperature (not measured)

Also measured during this run was air/fuel ratio (A/F ran from 13.0 to 11.4) and intake temperature at the intersection of the two Y-pipes (107.8 degrees Celsius maximum).

Observations:

1. A $450 boost controller and a $150 air intake system netted me nearly 15% more horsepower!
2. The peak torque was produced at 5180 RPM, but this represents the tail end of a power band that started at under 3000 RPMs (ie- we saw 350 lb-ft of torque at 3000 RPM)! The torque curve is wide and flat, which is why the car feels so strong and smooth. Some modifications can result in higher peak power, but drivability may suffer.
3. No detonation was detected. In a subsequent run, the dyno held the car at 5700 RPM at WOT while boost was manipulated. Any increase in boost over 1.00 kg/cm^2 resulted in less horsepower, indicating that the knock sensor was causing the ECU to retard the engine timing.
4. The injector duty cycle (IDC) maxed out by 6000 rpm, but the air-fuel ratio (A/F) was ~11.4, so the mixture was not excessively lean.
5. Power leveled off after 6000 RPM. Potential explanations:
   1. the stock 9B turbos are too small to flow more air efficiently
   2. the stock exhaust is too restrictive creating backpressure
   3. the ECU sensed that IDC was too high and reduced timing
   4. the cams are set up that way
6. Drivetrain loss was 30% at peak horsepower RPM! It's amazing the car gets 23 MPG!
7. Recommended reading: Understanding Horsepower loss through drive train

Corroboration:

When the MirageCorp Hybrid datalogger became available some years later, I discovered that my car with TD04-9Bs limited to 1 kg/cm^2 (14.223 psi) demanded 98% IDC (IPW * RPM / 1200) from 360cc injectors (stock AFR). With those parameters, Jeff's Fuel Injector Sizing calculator estimates 366.55 flywheel horsepower. Also, my car's trap speeds in the low 100s are consistent with the corresponding horsepower range on Jeff's empirical charts.

Comparison:

Dyno figures should be treated as relative rather than absolute, so it's most instructive to compare the results from all three cars tested, revealing the effects of various performance modifications. Here are the modifications for each of the three cars that would affect power:

Mike Chapleski's 1995 Dodge Stealth R/T TT (U.S. Spec)

22K miles, FIPK, stock TD04-9B turbos, stock 360cc injectors, stock fuel pump, wiring and regulator, Magnecore wires, .034 plug gap, DSBC @ 14 psi, Alamo DP, test pipe, Borla, Mobil 1 10W30 oil, Syncroshift in trans, ShockProof Heavy in xfer case, Centerforce DF clutch, 6-speed Getrag

Jim Matthews' 1994 Dodge Stealth R/T TT (U.S. Spec)

68K miles, FIPK, stock TD04-9B turbos, stock 360cc injectors, stock fuel pump, wiring and regulator, Magnecore wires, .034 plug gap, SAVC-R @ 1.00 kg/cm^2, stock adjustable exhaust, Mobil 1 10W40 oil, ShockProof Light in trans, ShockProof Heavy in xfer case & diff, original stock clutch, 6-speed Getrag

Roger Gerl's 1993 Mitsubishi 3000GT VR-4 (Euro Spec)

5K miles, FIPK, stock Euro TD04-13G turbos, stock 360cc injectors, stock fuel pump, wiring and regulator, Magnecore wires, .034 plug gap, DSBC @ 14 psi, AFC, ATR DP/cat, Borla, original stock clutch, 5-speed Getrag

Here is the combined graph for all three cars:

Observations:

1. An aftermarket exhaust system results in little to no horsepower increase when running boost pressure levels that the stock engine and fuel delivery system can support without detonation. An exhaust system moves the torque curve higher in the RPM range, sacrificing torque in the lower RPMs where the car is driven most frequently and marginally extending torque into the RPMs where the stock injectors are already maxed out.
2. The larger compressors (but same turbines) on Roger's Euro-spec turbos did not result in more peak horsepower but created a higher peak torque (around 4500 RPMs), and, had the tires on the car been rated for higher speeds, they probably would have extended the power curve into the upper RPM range.
3. Plug gap makes a difference. On Mike's first run, his plugs were gapped to .04x. Then he regapped his plugs to .034 and on his second run the car seemed stronger and resisted detonation. Plug gap also affects EGTs. On the drive down to Switzerland, Mike was seeing EGTs in the 975 degree range, but on the way back to Germany, he was seeing EGTs in the 925 degree range.

For more information, please visit Roger Gerl's dyno page.

Mikael Åkesson's dyno results are also on the web from his dyno session in Sweden. I also highly recommend Horsepower: Making it Add Up.