[changzuki]

With the battery now held at a steady 14 volts, the overdrive was now working as designed and it was time to look into the sluggish performance of the D850 and hopefully even find this intermittent and very annoying vibration.
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Pouring over past notes/comments did lead to an idea. I had optimized the D850 with the old three-rail 4-speed and rear 3.27 differential for 50-52 mph. That was the target and the sweet spot. With the substiution of the single-rail 4-speed with overdrive, things were now out-of-whack. For example, where 50mph was 2414 rpm, the same 50mph was now 1931 rpm and that's a huge difference, especially considering horsepower output is now going to be less at 50mph w/overdrive engaged... The nearly 500 rpm drop represents approx 1/6th the 3000rpm advertised limit of this engine.
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On a modern diesel or gas automotive engine, this may not be a big deal but consider that the old school Kubota D850 is of the fixed fuel timing type. This can be a blessing or a curse. In a tractor or a genset where you just slide the throttle lever to the "rabbit" and leave it there, this fixed optimization can be very beneficial, however, in autos the accelerator foot becomes bored quickly and the engine must respond to its needs/wants/desires. This type of variable input works against a fixed fuel timing system like the Kubota's D850, so if you're going to play in this area, be sure you know what everything downstream of the engine is, what affect it will have on something like the rpm, powercurve, bsfc, etc, and then see if it's possible to even match the timing to the drivetrain and your driving expectations.
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This is very time consuming, and if caution isn't followed, can have negative consequences on both the engine and your wallet.
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The reason for going through this self-created pain is quite simply this:
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The above is not a fuel log, but a snapshot of where Centurion currently stands with her economy.
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~CrazyJerry