Measuring Fuel Economy - Instantaneous and Otherwise

[SVOboy]

I agree with the happy medium part, darin (metrompg) thinks that's possible also.

Anyway, I see your point, and agree (I think, I'm wicked tired, it's almost 2am and last night was a 4amer, ).

The example I forgot was the new honda r18 engine that psyshack has, in which case I think slow acceleration is key. Under low load circumstances the engine changes it's intake valve timing to allow very little air and also opens the throttle (electronic throttle control) to WOT. So you're basically at wot but using very little gasoline. Honda states that this reduces pumping losses by 16%, which is HUGE, and also why I think a 1.8 with tons of power can get 50mpg in mixed driving.



PS: I like the way you think.

[Mighty Mira]

Originally Posted by SVOboy

I agree with the happy medium part, darin (metrompg) thinks that's possible also.

Anyway, I see your point, and agree (I think, I'm wicked tired, it's almost 2am and last night was a 4amer, ).

Yes, often the best situation is a point somewhere between two extremes.

The example I forgot was the new honda r18 engine that psyshack has, in which case I think slow acceleration is key. Under low load circumstances the engine changes it's intake valve timing to allow very little air and also opens the throttle (electronic throttle control) to WOT. So you're basically at wot but using very little gasoline. Honda states that this reduces pumping losses by 16%, which is HUGE, and also why I think a 1.8 with tons of power can get 50mpg in mixed driving.

Interesting. Very interesting.

I think this is Honda making the best of a bad situation, and this will definitely improve cruising FE. Remember though that there are still 84% of the original pumping losses still there that Honda can't do anything about. In which case if you have similar pumping losses but can produce twice the power for a fraction more pumping losses and then shut off the engine, you have halved the pumping losses effectively over the same distance.

Really, it would have to come down to testing.

One thing I notice is that there is a point where you put the accelerator down and you can feel a point of maximum torque at a given instant (and max torque at a given rpm is the same as max acceleration at a given rpm). Not sure how linear the fuel delivery is with the throttle, but this seems like a good first stab at where a max FE acceleration might lie. I naturally tend to accelerate like this anyway.

Trying to describe that point more, it's like the point at which there is maximum change in torque, where after that point there are diminishing returns from putting the foot down. I'm sure I'm not the only one who does this.

PS: I like the way you think.

Hey, I like the way YOU think. The ultimate point of this site is to save gas, and I love the way the members here are dedicated to empirical results. Theory is only as good as long as it has predictive value. When theory ceases to be predictive it is a sign that a new theory is needed.

Smart people modify their opinions/theories when new facts come to light. It's a good atmosphere here. I think it helps that we are all actually enthusiasts ourselves, we can all rush out and try whatever it is we are interested in, and that keeps us honest. We aren't discussing formula 1 cars, for example.

[SVOboy]

One thing that I wonder about this is that it would completely change my shifting pattern, which would skew results versus what I normally do. Anyway, I'll send you a pm about it because my it's a little involved and to no avail.

This really makes me was to learn to do something with the camshaft/intake valve timing, who knows...