The tandem rollers on the...
The tandem rollers on the Dyno Dynamics dyno showed the tires in perfect shape when rolling with no load. Under load, however, it’s easy to see how the tires begin to wrap around the smallish 12-inch roller. Future testing at various tire pressures and compounds is in our plans.
The engine was a pretty big 555-cube big-block Chevy running Pro-Filer heads and a street-friendly COMP Cams solid roller. With 8.9:1 compression, our engine was happy to gulp down even the lowest rank of pump gas swill and run like a champ. Of course, tuning would be a major factor in making sure the engine lived, and fortunately the use of a Holley HP EFI system allowed us to dial in the engine on the first dyno in our lineup, then keep it completely unaltered throughout the remainder of tests.
Eddy Current Chassis Dyno
Test and tune began at Carma Performance Engineering where Carpenter and co-owner Brad Mayo strapped the deuce to their Dyno Dynamics chassis dyno. Their eddy current dyno, similar to those offered by Mustang or Land and Sea, operates by having the wheels of a car spin a pair of drums that has a metallic rotor attached to the end of one drum. The rotor, which looks like a giant brake rotor, spins within a field of electromagnetic coils. The operator basically adjusts power to the coils, which can slow the spinning rotor down or allow it to speed up, and measures the power required to do this. Then the dyno software does the hokeypokey to determine the horsepower produced.
It sounds a bit complicated, and it is, but the upshot is that with this type of dyno a load can be applied and held at any rpm or allowed to run a sweep through the rpm range, giving tuners a great chance to complete 95 percent of driveability and race tuning without the tires touching pavement.
On our little project, Carpenter began the process of converting the tune from a turbocharged race-fuel setup, to a naturally aspirated pump-gas tune by merely connecting his laptop to the HP EFI ECU. Using a wide-band oxygen sensor stuffed in the tailpipe and comparing against a second oxygen sensor hooked up to the HP EFI, he was able to simply enter the desired air-fuel ratio into his laptop, hit the Self-Learn button and let the Holley system do most of the grunt work getting the fuel map set up. Final tweaking was done manually, and it was time to see how the car baselined.
Running the engine to a harmoniously high rpm without any bad noises was music to our ears, though we were slightly surprised at the dismal power the computer screen displayed. We saw the raw power numbers and asked Carpenter to display the corrected numbers so we’d have a better comparison against the other dynos. Unfortunately, with the weather being good and cold, it actually corrected down to 487 horses at the peak point of 5,400 rpm with torque maxing out at 476 lb-ft at 100 less rpm. The power never went higher, so we stopped the pulls by 5,700 rpm.
We figured the converter and automatic tranny hurt us some, but still had hoped for more considering the cubes involved. But hey, maybe the next test would boost our spirits!
Test two brought us to Carthage and the Dynojet chassis dyno of C&C Motorsports. Owner Casey Lawson is a regular drag racer and has run his dyno long enough to see that actual dyno numbers versus track times can vary greatly by the torque converter and tire design. As we strapped the Nova down, he related that the inertia-style dynos, while lacking in steady state control, offer a more real-world version of power because they allow the engine to accelerate at its own speed, like at the track, rather than a predetermined speed.