Speed vs. "sweet spot"
#31
11-11-2009, 04:02 AM
i've been thinking about this thread alot the past few days.
maybe my theory about how you take off and where you shift is motor. as i said before my s60 gets great milage short shifting.. while my truck was down i had a columbia with a acert c15.. 5.86 mpg... ran 70 @1500 rpm i short shifted it and babied the hell out of it.. oh and it was a 410 hp motor.
#34
11-11-2009, 02:20 PM
short shifting, or progressive shifting, is about grabbing the next gear at the lowest possible revs. In the lower gears, you are shifting up from idle through 5 or so, at 1000 increasing to 1500 or so, in steps, as low as it will still pull in the next gear. As you get to the mid and higher gears, you have to spin it a little faster, since those gears won't pull too well from way down.
Figure, the goal is the fewest number of ups and downs of the pistons to get you up to speed. Spinning the engine to 1500 and beyond in the lowest gears isn't needed and just wastes fuel. money in your pocket or up the stacks, your choice. Need a YouTube video to demonstrate the technique
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#35
11-15-2009, 06:23 AM
When I encounter 30mph sustained crosswinds (which usually come with higher gusts) while I'm empty, I will drop my speed considerably and I still get 4.5mpg, just the same as if I drove 75. I know that because I'll do 75 in a big crosswind when I'm loaded and guess what: I get 4.5
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Pessimist,- is just well informed optimist!
#36
12-12-2009, 03:22 PM
rpm hp torque 1200 450 1969 1300 475 1919 1325 481 1906 1350 490 1906 1375 500 1909 1400 510 1913 1425 520 1916 so the highest torque is at 1200 rpm as it should be and then it goes down at 1325 and 1350 rpm, and starts rising slightly again at 1375. the dyno guy said, "drive at 1375 rpm minimum when loaded" but the above numbers don't prove that's true, as at 1300 rpm i have more torque than at 1375 rpm! with my 512 rpm tires, 3.73 axles and 0.73 13 speed, i do 56 mph at 1300, 57 mph at 1325 and 60 mph at 1394 rpm. i'm driving from alberta back to civilization on 11/17 tomorrow and will try driving at the superslow 56 mph. my load is about 30,000 lbs. i drove at 58 mph (1347 rpm) today from regina, sk and due to harsh weather and winds, my fuel mileage was worse than usual  i have a digital tachometer in my gearmaster and the difference is about 50 rpm between that and the analog one on the dash. this is a very interesting discussion as i've been thinking of changing my axle ratio to 3.58 or even 3.42 to be able to run a bit faster, but maybe super-slow speed is the answer? btw, the speed limit on 11/17 in northern ontario is 90 km/h (56 mph) which is perfect for my little experiment. will publish results in my blog on the trip completion.
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#37
12-13-2009, 02:39 AM
I used to have a "cool" truck that averaged 5.17 mpg for the entire year.
why didnt you get it fixed?
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