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Old 04-18-2012, 04:51 PM   #82 (permalink)
serialk11r
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Quote:
Originally Posted by IamIan View Post
Well at least that is a starting comparison point.

I suspect that is not the peak efficiency point ... on a BSFC chart ~26% works out to around ~300 g / kwh ... There are many ICE's including Gasoline ICEs that do significantly better than that ... so While that might be a fair estimation of one point on the BSFC ... I do suspect it is not the peak efficiency point.
300g/kwh is middle of the pack at "low speed" (below 70mph, because people love going 80) cruising I believe. Cars with strong acceleration and/or bad gearing will cruise in the 400s, weak cars can manage maybe a bit better than 300 at 60. Peak efficiencies on a lot of engines is getting to the high 30s(%), or around 230g/kwh, but that occurs at unreasonably high load levels for highway cruising.

As a quick example, on the upcoming FRS/BRZ/86 the automatic uses the exact same ratios as the IS250 with slightly shorter final drive, and it puts 60mph at just under 2000rpm. This leaves not much power for hills, and at 80mph you'd probably having the engine at ideal load levels for efficiency already. At 60mph the load is still something like only 30%, which may or may not land you below 300g/kwh. That car is very low and has a reasonably good coefficient of drag so that reduces the power requirement and efficiency by a bit though. I think this is realistically the longest top gear that an OEM would try to use, in terms of available excess acceleration.

Last edited by serialk11r; 04-18-2012 at 04:59 PM..
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