Quote:
Originally Posted by cfg83
Question for someone else (basjoos?) : What's the cleanest MPG test you have seen on this site? For aero mods, it's the "coast-down a hill to a stop" test that is best, right?!?!?!?
CarloSW2
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High (very) speed coast down w/ a video cam on the dash for decent speed/time accuracy imo. Coasting to a stop can add a lot of error since the time from 30-0 is generally way more than the time from 60-30, so the difference in two profiles is harder to spot. It may be ~21s/23s compared to 6s/8s and there's a larger window for other stuff like weather to influence the results. At 90mph an average'ish car may need ~24kW for aero and 6kW for rolling. At 45mph it's only about 3kW for each, and a ~23mph it's only ~.3kW for aero and 1.5kW for rolling. The slower we go the harder it is to pick up any difference in aero. And... to complicate things, I think (this right treb?) the drag coefficient changes compared to speed, so that's just one more variable, although Iono if it's significant for car speeds. In any event, a 12% improvement in aero will result in ~27kW needed at 90mph versus the usual ~30kW, but at 45mph the difference is only~5.65kW compared to ~6kW, and at 23mph it's pretty well unpossible to figure a difference. Ideally, we could all get together and head out to the salt flats w/ a cam to do some timed decels. Newbs are limited to 140mph max speed IIRC and have to have all the safety equipment, but I'm sure 120-100mph could give us tons of great data on how certain mods influence certain cars. And, for a car like my veedub, that's gonna be limited by power, the top speed may be noticeably higher if the mods are as effective as we think they are.