Quote:
Originally Posted by swineone
My car has a shift indicator, and it appears that, as long as the current speed is such that next gear will be at 1500 RPM, it wants me to shift. For a while now, I've delayed shifting so that I'm closer to 2000 RPM rather than 1500 RPM at the next gear. The turbo lag is especially noticeable under 1500 RPM, with a transition band from around 1500-2000 RPM, and at 2000 RPM I can get full torque.
I was basically afraid of lugging the engine (note this is a 3 cylinder engine), or of being in an inefficient region of the engine map. Maybe I should experiment with following the shift indicator's advice.
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The Insight's original engine is a 1.0L 3 cylinder non-turbo with lean burn at part throttle, and very tall gearing - around 1700rpm @ 80kph. Because it lacks a turbo, its efficiency zone may be very different than your vehicle's. Manufacturers very rarely publish BSFC maps, and even doubly so more recently - I don't think I've ever seen one for a modern GDI turbo engine, so it's pretty hard to advise based on published data.
That said, Honda went to great lengths to maximize economy, often at the expense of all else.
Its shift indicator light has some logic which seems to take load into account, but basically it comes on if it could possibly be in a higher gear above idle speeds, or above maybe 2000rpm with accelerating.
This is slightly oversimplified, but when cruising, it leans out to ~24:1 AFR, which allows very high loads when cruising, often above 75%. Even slight grades may need downshifting to maintain speed. It will attempt to hold onto lean burn until maybe 90% load, at which point it drops back to stoichiometric for more power. Below maybe 2500rpm, one of the two intake valves only opens a hair.
The strategy seems to be to get load up as high as possible, as much as possible. It will happily cruise or even accelerate (albeit very slowly) as low as 1000rpm and not suggest a downshift until the pedal reaches the floor, and even then not for a few seconds.
I can't advise if avoiding boost is more or less efficient, but the shift light can probably be trusted.
Quote:
Originally Posted by swineone
Do you do P&G, or just cruise at a low load?
I've gotten so used to P&G that I just do it automatically. If I have the car in gear for too long, I start getting jittery. When I got this car I learned how to do a proper double clutch so I can engage back after a glide with minimal jerking. It's just too bad the car doesn't tolerate EOC.
However, I'm not sure how helpful P&G actually is -- and one of the things I had in mind with starting this thread was to figure out the optimal way to perform a pulse. This car is underpowered at low RPMs without boost, and the gearing is very tall (it sure could use a 6th gear), so maybe P&G is not really necessary -- especially considering I can't EOC it.
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With the stock engine, I found P&G without EOC to provide minimal gains, but P&G is largely a tactic to get load up, and secondly to minimize other engine losses (allow average engine RPM to be lower), and Honda already did a good job getting load up. However, there were significant economy gains to be found if I killed the engine any time there was a downgrade where I could coast without power for more than maybe 5 seconds.
With my new engine I have an even taller top gear, but the amount of torque available makes it such that load isn't very high when cruising, often at or below 25%. I see moderate gains from P&G, and large gains from EOC. I'd say under the right conditions, the improvement can approach 50%. It's kindof a pig, and the less time it spends running, the better.
With my previous car, gearing was very bad for economy. In that one, I could see gains as high as +80%. So, I'd say P&G shows diminishing returns the taller your gearing is, or the smaller your engine is.
Let's hope someone else can speak from personal experience about boost. I wish I could advise on that. With older engines, boost was definitely to be avoided, but that very well may not apply anymore.