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Hi Plumma,

There is only a difference with respect to the governer characteristics that are change fueling to suit the auto. Should not reflect in a power difference.

I am interested to hear what you say on fuel economy. I was referring to final drive of gearbox (or is the OD in the transfer case??) anyway, for the manual it is 0.84, for the auto it is 0.716. Diffs in Australia were (I believe) all 4.11. Some Jap spec and US Spec received 3.73 in their manuals.

10.5L/100km is excellent economy, about the best I have heard. Not everyone gets this economy. It could be that your engine is well loosened up, your injector pump timing may be advanced more and your injector spray pattern may be better. Mostly these are the issues. Even things like thermostat temp. If the engine runs hotter, there is more potential for work. This is however a small variable.

I have heard many reports from people with very high km 12HT's reporting excellent economy - even with injectors that need to be replaced. This could be an issue too. As the injectors wear, their cracking pressure decreases and this has the effect of advancing the timing. Up to a point, advancing the timing a few degrees can help considerably with economy, at the expense of some noise increase. On my 540kkm engien, the cracking pressure was only 180 bar. Std they are set to 210 Bar, so this is a considerable drop in pressure. How this reflects in timing change exactly (degrees advance per % drop in pressure), I do not know.

When rebuilding my current 12HT in the HJ61 (which I started for the first time yesterday), the bores were well worn at the turn around point; very common problem in the 12HT. I used a snapon parrallel hone to bore out the cylinders until the lip had dissappeared. This put the pistons and the rings out of "new" spec tolerance. In fact, out of spec completely on pistons, but in spec on the rings (0.7mm gap. For rebuild 0.2-0.45mm, for worn engine up to 1.2mm). In any case, I filed back a set of oversize rings to 0.4mm gap and got a piston, heated it to ~ 180 degress and tried it in a well lubricated bore for a fit. Well, it "only just" slid in. Very nice fit and wouldn’t want it any tighter. The aluminium/silicon alloy pistons have a much greater coefficient of expansion that cast iron and will be at a temperature higher than the water cooled block. A friend of mine knows of people that build their new engines this way - heating the pistons, checking hot clearance etc with quite impressive results.

In essence, what I am saying is that it may be (I am hoping) that my engine with looser piston to bore clearance but better sealing rings, *may* do the 10.5L/100km if I advance the timing a few degrees. I will share all the measurements with folks. It is an interesting experiment. I am in the quest for great economy and this is a major reason for wanting to keep revs as low as possible on the cruise. Typically a diesel is most efficient at full load and 1700-1800rpm. Note that HJ61 manual does about 2550rpm @ 110km/h with std 31" tyres, so I am very (happily) surprised to hear such excellent economy from the manual when doing these sorts of revs.

By the way, visible smoke turned out to be not such a great yardstick for fuel economy as I had initially thought - it seems to be reasonable to think so, but there are many other factors governing fuel economy.