Quote:
Originally Posted by orange4boy
I have a couple of questions about a couple of possible issues with throttle stop testing. In order for this type of testing to be reasonably accurate, both the environment of the test location as well as engine power output would have to be constant over the full period of testing.
As I understand it, fuel injected cars change the air/fuel ratios pretty much constantly with changes in engine temperature, etc and the Insight, in particular, has it's lean burn mode that happens automatically. This seems to make a big difference in throttle position/speed as I have noticed and I think MetroMpg noted as well.
Are you controlling for this in your tests?
The other is atmospheric effects which can change engine power significantly, which I'm sure you are aware of. Barometric pressure can change dramatically in the space of a few hours in extreme cases, so one should probably keep tabs on that especially if tests are done on different days or times of year. Humidity also plays a role in engine power.
Have you taken these into account?
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1) Technically, we'd never know if the BSFC was drifting around on the engine map.
2) And in the past, it was discovered that 30% of streamlining benefit could be lost if gear-matching wasn't accomplished to keep a constant load on the engine after aero modifications.
3) With modern, EFI, and high sampling rates, compared to carbureted vehicles, it may be that BSFC isn't as unstable as in the past. I couldn't prove it one way or another.
4) Universities competing in the mileage marathons typically have a fuel tank that can be weighed to ascertain the mass of fuel consumed over a measured distance. Thermal volumetric expansion wouldn't enter into the calculus. The only unknown you're solving for is mpg based upon the fuels mass. Easy.