burn and glide @ 70mph

[Snax]

Originally Posted by Snax

Using our 5280 baseline rpm, let's assume that we double our top rpm and top speed. If we only need to do that for 2 miles and it provides a coasting distance of 8 miles at 850 rpm for instance, then assuming an instantaneous peak to our maximum rpm, we have 2 miles x 10560 rpm plus 8 miles x 850 rpm. That works out to 27920 total rotations for the total ten miles travelled, and 2792 rotations per mile, or 1.89 ft/rotation - cutting our parasitic drag from the motor nearly in half.

I neglected to take this to the obvious next step which would be EOC'ing for the 8 miles. This drops rotations per mile down to 2112 or 2.49 ft/rotation - a nearly 150% improvement in efficiency for every revolution the engine actually turns.

YMMV. :P

[goodella@hartwick.edu]

Sorry for skipping through posts.. butI wanted to say that some trains now use a gasoline engine (probably diesel) with an open throttle at the point of most power (15k rpm on some) to charge batteries that actually run the train. This is more efficient than just running at medial rpm constantly.

[DRW]

Hondaaccord98 wrote:" ...and probably hard on the car what with 65 mph reengagements from idle and many into neutral and then to 5th gear shifts as opposed to just keeping it in 5th. If I destroy my transmission I probably lose out expense wise ... gas $ saved is less than $ for a new transmission. "

Those maneuvers are not supposed to be abusive to the tranny. When I shift from neutral to 5th I like to open the throttle slightly to get the revs up a little, then engage the clutch gradually. It only takes a half second to do it this way.

Here's another reason for gentle rev changes. I noticed in my car that if I go from neutral to 5th and dump the clutch so the revs rise quickly, then the O2 sensor readings show a richer A/F ratio for about 1/2 second. If I engage the clutch gradually and bring the revs up carefully, then the O2 sensor stays lean. My theory is that my car has an accelleration enrichment function that applies to rapid rev changes, not just rapid throttle changes like traditional accel enrich. I also found that my car has a decel enrichment as well, so I learned to get off the throttle gradually, too. I have a feeling this isn't unique to my car, other modern fuel injected engines may have a similar strategy to maintain smooth power delivery.

[Snax]

That's an excellent point Dave. It is also one of the reasons most cars these days are being built with electronic throttle control, so that the manufacturers can reduce the impact on emissions through sudden extreme throttle changes. My understanding is that a controlled decel is common to reduce oxides of nitrogen - which suggests to me that it is kept on the slightly rich side during this controlled decel period. If a person were to limit decelleration beyond the point at which the computer kicks in, they can likely decrease fuel consumption slightly. Conversely if one isn't attuned to the dynamics of the computer, they might burn more fuel by controlling the deceleration themself.

I doubt it will make much difference over the course of a full tank, but it's just one more wrench in the box at your disposal.