Most of the main points have already been addressed by others ... just my own 2 bits on the topic.
There are different pros and cons... stemming from the combination of two things:
#A> What method uses the least total joules of energy needed to travel a given route, under given conditions ( average speed , weather, traffic , etc. )
#B> What method maximizes the highest average ICE conversion / operating efficiency to convert fuel energy to travel energy in order to provide the energy needed for #A above.
You can 2x the #A travel joules , and 2x the #B average efficiency ... and would still result in the same FE or MPG.
Does speed variation increase #A ... yes, absolutely.
But if that speed variation allows for a higher #B ... than a non-varying speed would have ... it can potentially produce a net benefit... despite the increase in #A.
If you can get any amount of increase in #B without a increase in #A you are net better off... or any amount of decrease in #A with no change in #B.
Quote:
Originally Posted by niky
I'm pretty sure that's just about everything with computerized fuel injection. There are those that still inject a miniscule amount during engine braking, but it's a tiny percentage of what you use while idling.
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For my 2 bits.
Engine braking is best used as just that braking ... otherwise ... it isn't as much about the potential for tiny amounts of fuel ... some cars do due fuel cut during engine braking ( and consume nothing ) ... but the engine braking losses from air pumping and friction of just rotating the ICE add up... that is loss that often has to be paid back latter... if you want to brake anyway that's fine ... but if you don't want to brake , then don't.
For example of the engine braking air pumping , friction losses , etc.
I see about
~2.67 kw @ ~1,365 RPMs
~2.98 kw @ ~1,682 RPMs
~3.41 kw @ ~2,107 RPMs
~4.67 kw @ ~3,364 RPMs
That is lost power any time the ICE is turning ... and one of the potential benefits of P&G techniques... if used under the right conditions.
Quote:
Originally Posted by Arragonis
The instrumentation available - built in or add in - isn't accurate enough to determine which is better in one run or a collection of runs really but they give a guide, better than nothing.
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If one is motivated it can be measured and determined in as little as one run of each method.
Once you know the ICE's BSFC warmed up ... and once the ICE is warmed up ... you only need a few pieces of real time data.
#1> ICE Load
#2> ICE RPM
#3> Vehicle Speed
#4> Weather Conditions
With #1 and #2 and a BSFC you know the real time operating efficiency of that warmed up ICE ... over the run you can average it out to measure the average % ICE Effiiency for that method.
With #3 and #4 you can quantify and determine any travel joule differences between the runs.
A real time operating % efficiency meter is one of my dream Mods ... I may never get it ... but definitely on my wish list.