[changzuki]

Details #7 - Coasting to victory!

In the ecomodder world miles per gallon is the supreme goal - the Queen Mother Mary, and to what end will these folks go in their quest to attain the highest of the high?

In this final installment of the details we'll take a last peek at something that helped Centurion coast its way to a victory at the 2014 Green Grand Prix!

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Some engines have it - some engines don't.
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Metro 6/1 (Listeroid diesel one-lunger): 1.43L (1430cc) or 87.26 cu in
Bore and Stroke: 114mm x 139.44mm (4.49in x 5.49in)
B/S ratio = 0.817 - under-square
18:1 compression ratio

Changfa CF186F: 406cc single cylinder
Bore and Stroke: 86mm x 70mm (3.38in x 2.76in)
B/S ratio = 1.228 - over-square
20:1 compression ratio

Kubota D850: 855cc or 52.2 cu in
Bore and stroke: 72mm x 70mm (2.83in x 2.76in)
B/S ratio = 1.025 - slightly over-square
22:1 compression ratio

Each engine above is a piece of the experiment here in Colton, NY.

The Metro is inside the house and when called upon will generate electricity as well as heat at a leisurely 375 rpm.
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The Changfa CF186F is the engine adapted to the Suzuki GS550 to make the 115mpg "Changzuki" diesel motorcycle.
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And of course the Kubota D850 powers the Centurion.
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In case the photos above did not tip you off, the focus is one one single item that has been very useful in these engines:
The decompression lever!
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Normally the decompressor aids in starting these engines, but is there another use?
During the Green Grand Prix, Centurion didn't EOC (engine off coast) - or did we? We also didn't PNG (pulse and glide) - or did we?
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What we did do was to take advantage of a couple of features "just in case". In this context "just in case" was the proverbial "Hail Mary Pass" a team sometimes resorts to when winning is within their fingertips.

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Centurion's Hail Mary Pass - Here's the idea:
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When Centurion coasts in gear (foot off throttle, momentum drives engine) fuel delivery is effectively stopped. During this time if the conditions are right for coasting any appreciable amount, it's a great opportunity to engage the decompression lever and allow the engine to spin without the resistance of cylinder pressure. This allows for continued circulation of the cooling and lubrication system, without the need of an engine restart mechanism, all while coasting/consuming no fuel.

This is a neat compromise when compared to: disengaged clutch/engine-off-coasting /vs/ disengaged clutch/engine-idling-coasting /vs/ engaged clutch/engine-fueled coasting.

As mentioned earlier, Centurion's governor takes care of the fuel cut when coasting so the only real challenge was to incorporate the decompression lever to engage (and disengage) at the correct times.

This was quite easy to do!

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Tailoring the decompression lever for the Green Grand Prix:
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Basically out-of-sight out-of-mind, the decompression lever is located at the rear of the valve cover on the Kubota D850. Engaging it requires very little effort and disengaging is assisted by a return spring. It seemed logical to be the "computer" to manage the idea since the driver could look several seconds ahead and determine the frequency of use for the decompressor. Computer problem solved, all that was left was the physical function.


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A horn button, wire, and a trunk release solenoid:
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Really? Really! How's that for high-tech? Knowing Centurion would be using a battery for the on-board cameras made the choice to go "electrical" for this addition an easy one. The solenoid was mounted lower under the jumble of firewall wiring harness and a fairly stiff wire joined it to the decompressor lever. Two insulated 16ga wires ran from the solenoid to the momentary switch (horn button) that was located on the bottom-side of the clutch pedal. An additional power wire to the fuse block supplied the circuit with battery power.
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Anytime coasting was advantageous, simply letting off the accelerator pedal would cut the fuel and then using the top of thy left foot, the tiniest of pressure to the horn button located on the backside of the clutch pedal would activate the trunk solenoid and engage the decompression lever
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and coast-we-would! This process was basically invisible and seamless to the casual observer. There was a slight learning curve when on the racetrack at the Green Grand Prix but after the first lap I knew exactly where I wanted to use it and use it I did! Weeeeee-weeeeeee-weeeeee!
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~CrazyJerry
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