Combined with the air temp sensor located just upstream of the throttle body, we could track air heating from the Eaton M62 during a dyno pull, and could, alternately, datalog turbo compressor discharge temperature upstream of the air cooler unit for post-dyno analysis of intercooler efficiency.
We measured exhaust backpressure during turbo boost and, alternately, intake pressure upstream of the throttle body on either end of the air cooler when the supercharger was installed so we could separate boost produced by the supercharger from boost produced by the turbo.
Up to this point, we had dedicated the Aux Volt Motec input to a 1-Bar MAP sensor providing barometric pressure compensation. We could free up the aux volt port to measure backpressure or compressor-discharge pressure by reconfiguring the load calc scheme to provide barometric pressure compensation using a manually entered parameter. By swapping out the 1-bar GM MAP sensor and installing a Delco 3-bar or Data Instruments 100-psi pressure sensor, we could datalog exhaust or compressor-discharge pressure to approximately 33 or 75 psi.
New Dyno Results
Dyno Run #1
We performed our dyno testing at Alamo Autosports with Brice Yingling and Bob Norwood, and started with a nice, low-boost pass. We unscrewed the wastegate adjustment bolt almost completely. The boost table was set to bring in a full 170 kPa (10 psi) of boost at 3500 rpm on 93-octane.
We connected the water cooler to a tap water source, with a total-loss drain-back into the sewer, the blower-discharge sensor to the aux temp port on the Motec, and a pressure gauge to the front bank exhaust pipe.
In the "soft" dyno run, boost increased to 175 kPa at 3500 rpm and fibrillated between 185 and 200 kPa at more than 6000 rpm. No one watched the new backpressure gauge on this run. Torque was fairly flat, from 3750 rpm at roughly 365 lb-ft, before falling off gradually above 5600 rpm. Peak power of 394 hp occurred at 5900 rpm. The auxiliary temperature in the blower discharge climbed from 108-degrees Fahrenheit to 124-degrees Fahrenheit. The intake air (air-cooler discharge) temperature stayed at 82.4-degrees Fahrenheit.
Dyno Run #2
The next run was a "hard" dyno run, with power up by 20 hp and torque up approximately 15 lb-ft over the same range. We were again on 93-octane pump gas.
At this point, the torque leveled off at 4100 rpm and stayed fairly flat to 5600 rpm. Boost (MAP) climbed to 212 kPa at 4100 and fibrillated to 207 kPa at 6700 rpm. Peak power of 415 hp occurred at 6200 rpm, with peak torque measuring at 390.3 lb-ft at 4300 rpm.
This time, we watched as the turbine-inlet exhaust backpressure, which was insignificant in the early run, climbed to 15-20 psi at peak power. It was difficult to tell exactly because exhaust pulsations made the needle flutter.
The blower temperature sensor seemed to have heat-soaked to 118 degrees at the beginning of the dyno run. The blower air temperature climbed steadily to 126 degrees by 5750 rpm, then increased to 140 degrees at 7000 rpm.
Dyno Run #3
With the MR6's fuel tank nearly empty, we added five gallons of 118-octane race gasoline.
Previously, we discovered that with the wastegate adjusted to the minimal 6-psi setting, exhaust backpressure pushing against the wastegate poppet valve prevented the turbocharger from making more than 22-24 psi boost because the wastegate was opening prematurely. The obvious answer was to clamp down on the wastegate adjustment bolt to preload the wastegate actuator spring a little harder. However, we were about to discover that this solution produced blowback in a new problem.