Quote:
Originally Posted by Arragonis
I'm interested in researching this in my TDI a little more. The gearing in 6th is very high and I have experimenting with lugging in a high gear with as little throttle as possible to maintain speed and going into a lower gear and doing the same.
I haven't come up with a complete answer, sometimes the higher gear is better and sometimes the lower one is. I do the same route and try different things but its a toss up as to which one wins.
How does BSFC work for this ?
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Since your diesel is unthrottled and suffers no loss of compression that comes with manifold vacuum, the BSFC chart is much more broad and fairly consistent over a larger range of loads than my VX lean burn throttled gasoline engine. The two BSFC charts for those two very different engines would be a real contrast.
It may be your "complete answer" is that you have a much more flexible range of efficient engine power production to work with and your best choice is a lower gear that allows you to climb the grades in less time than a max load gradual slowdown in a higher gear ascending the same grade.
The difference in consumption would probably only become significant if your average speed was significantly lower in the higher gear. Depending on the length of climb on the grade, you might try approaching at a slightly higher speed and bleeding speed very gradually in a higher gear, but I would bet the overall mileage would not change significantly as long as the average speed was similar in your comparisons.
regards
Mech