Quote:
Originally Posted by Drifter
Time trialists & triathletes often use the chung method to test their CdA on their bicycles and it has helped bring effective aero testing to the masses (or at least cyclists with quality power meters). Has anyone done anything similar for cars?
Are there any good, affordable, OBD2 data loggers? My scangauge shows horsepower & speed, but I can't log with it... |
1) It wouldn't be recognized as something the industry has used, or presently accepts as a test protocol.
2) Universities, as the University of California, at Davis, California, use fuel mass consumed, over a measured distance, under continuously-monitored conditions, and then, data reduced to SAE standard conditions.
3) SAE also has a specified Coast-Down test procedure, however, it is so rigorous in it's requirements, it's my opinion that, no one here should attempt it.
4) I paid CAR and DRIVER technical staff to coastdown-test one of my experimentals at the Chrysler Proving Grounds, on a track specifically designed for that purpose, under conditions within the constraints for the test, with continuous weather monitoring conducted, recorded, and time-stamped, exactly as specified by the SAE, and data-logged information fed into a custom computer program constructed specifically for coastdowns, which respected all test parameters as specified. A phone call would tell you if that was still an option.
5) Top speed has always been recognized as an indicator for efficiency-related testing. It is limited by the requirement of performing back-to-back runs, with and without modifications.
* Proving ground tracks, while allowing for 'paved' surfaces and real-world rolling resistance, suffer curve-resistance penalties which jade actual top speed potential.
* The Bonneville Salt Flats offers a straight-line 'laboratory' of sorts, although rolling resistance on the salt can vary by the minute due to 'traffic', and the occasional rain storm. There are three weather stations there at Rick Gold's Racing Fuel, plus the airport at Wendover.
Again, you must have the capacity for quick addition or subtraction of modifications in order to parse out any changes.
6) Full-scale wind tunnel testing for us is now basically limited to A2 Wind Tunnel, Aerodyne Wind Tunnel, and Gene Haas Racing. Lockheed-Marietta, Georgia used to accept all comers. Availability was an issue in the past due to NASCAR purchasing all available time for years in advance.
7) OBD-II -sourced data ought to be valuable, if you can give it a pre-conditioned, two-way, constant-speed test-period enough time to average out spikes. And I'd caution you not to defeat any sensory input to the CPU, as it would render critical EFI, ignition timing, and BSFC optimization impotent.
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