Going up steep hills- downshift or floor it?

[IamIan]

Originally Posted by jtbo

at steady speed 26% efficiency put into calculator is giving correct results.

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.

[serialk11r]

Originally Posted by IamIan

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.

[IamIan]

Originally Posted by serialk11r

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.

I guess I've been spoiled ... although as you suggest the peak efficiency point is at higher loads and RPMs ... my ICE has a fairly wide ~35% efficiency point that fits well for highway cruising in a window a bit under 30% load to a bit over 80% load.

[serialk11r]

35% at 30% load is certainly superb. What can I say, you have a nice car

[jtbo]

I'm driving 50mph or under, at 50mph there is 1800rpm and at hills can go as low as 1200rpm if I keep top gear, but I guess my car has shorter gearing than many US vehicles?

[IamIan]

Originally Posted by serialk11r

35% at 30% load is certainly superb. What can I say, you have a nice car

Thanks ...I think so too.
It has spoiled me ... the ICE in it won engineering awards for every single year of the 6 years Honda built it.

Although I like it ... there was technological room for improvement back 13+ years ago when it was designed ... and there is even more technological room for improvement now ... either OEMs get to it ... or eventually if they take too many years ... eventually I'll make improvements myself.

[redpoint5]

Originally Posted by jtbo

I'm driving 50mph or under, at 50mph there is 1800rpm and at hills can go as low as 1200rpm if I keep top gear, but I guess my car has shorter gearing than many US vehicles?

You are getting 36 rpm/mph, which is about average for most petrol cars. Don't you have a diesel? It's a bit high if so.

My TSX is 42 rpm/mph

The motorcycle, maybe 85 rpm/mph

My diesel truck with oversize tires, about 27 rpm/mph

Just bought a Jeep Liberty that does 33 rpm/mph, but it only gets 18mpg