I drove to/from Portland today. Decided to do a speed/mpg experiment. Usually I drive w/traffic, which means cruising around 3000rpm/75mph. (I have 33's w/stock gears.) Over many trips, 13mgp is pretty standard at this speed. Today I limited myself to 2500rpm, which is just under 65mph. I got 16mpg - pretty good for a brick. I figure I saved 5 gals of fuel, at the cost of nearly an hour in extra time. Not sure if this was a good tradeoff, but I was happy to see what kind of milage was possible. Anybody want to try 60mph?
"Free" 3mpg gain! (1 Viewer)
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Ive pulled down 17 before with 30s going about 60 mph. Its amazing what letting up on the skinny pedal will do for mileage.
How do you calculate your mileage with the 33's?
I recently mounted 33's but haven't given my mileage much thought. I know dividing the tripometer reading by the gallons it takes to tank up won't work, that's what I used to do anyways.
I recently mounted 33's but haven't given my mileage much thought. I know dividing the tripometer reading by the gallons it takes to tank up won't work, that's what I used to do anyways.
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I've used both gps and hwy mile markers to calculate a speedo conversion factor for my tires. It's actual X 1.15. ie the speedo/odo reads 15% low. Also, maybe boring trivia, I've plugged these numbers into a gear calculator, to find actual tire size, and it's 32." I guess I could use a tape measure too...
What psi do you run your tires?
I bet your overall tire dia. is larger w/ those 9.5's than the 10.5's I'm running.
AT or MT tire?
I bet your overall tire dia. is larger w/ those 9.5's than the 10.5's I'm running.
AT or MT tire?
surfpig
The Anti-Tech
lovetoski said:
That's how I learned my conversion factor, came out to about 16%. For easy math, I use 15%. Mileage on my 55 runs roughly 12mpg or so going between 60-65mph. I got 16 once, driving like a granny. Might have to get a pair of those big plastic sunglasses!
You'd get better mpg @ 55, & it continues to increase until it's infinite if you just stay home.
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Boring tech stuff: 
MPG increases as the RPM approaches best BSFC, which is about 1800 for a 2F.
The BSFC curve takes a dump past 2700RPM, which combined w/ the increasing aero drag, explains the horrendous MPG numbers some 60 drivers see.
MPG increases as the RPM approaches best BSFC, which is about 1800 for a 2F.
The BSFC curve takes a dump past 2700RPM, which combined w/ the increasing aero drag, explains the horrendous MPG numbers some 60 drivers see.
I've always wondered where that point was on our engines, no joke. Does that point shift in a worn engine? Does it go down?
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I think the whole curve gets worse as the ring and valve seal wears away, but I don't think the shape or critical points move up or down the RPM scale.
It usually shifts toward lower RPMs when measured at part throttle, but the only chart Toyota published in English was the typical torque and BSFC @ WOT graph. So it's hard to say where best BSFC is at 60% throttle.
It usually shifts toward lower RPMs when measured at part throttle, but the only chart Toyota published in English was the typical torque and BSFC @ WOT graph. So it's hard to say where best BSFC is at 60% throttle.
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FJ40Jim said:Boring tech stuff:
MPG increases as the RPM approaches best BSFC, which is about 1800 for a 2F.
The BSFC curve takes a dump past 2700RPM, which combined w/ the increasing aero drag, explains the horrendous MPG numbers some 60 drivers see.
Kinda interesting tech stuff I think...
What is BSFC please?
So if you keep speed constant, and change diff ratio's/tire size to reduce engine rpm, mpg would go up? (Assuming you aren't going so fast that aero drag wipes out any advantage.)
I notice my 60 rumbles around town pretty nicely at 2000rpm...
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BSFC = Brake Specific Fuel Consumption. It's the ratio between fuel burned and work done. It is usually plotted as a curve of RPM on the bottom axis and fuel burn in mass per power unit on the vertical. The lowest point of the curve is the RPM where the engine is most efficiently converting fuel into work.
Yes, MPG will go up as RPM's drop down to the best BSFC point. However, in the real world if we geared a FJ60 to turn 1800RPM @ 60MPH, the engine might not produce enough power @ 1800RPM to push the vehicle through the air at that speed. IOW, RWHP could be less than road HP. Someone more motivated than me can get the calculator out and figger out the RWHP @1800RPM.
Yes, MPG will go up as RPM's drop down to the best BSFC point. However, in the real world if we geared a FJ60 to turn 1800RPM @ 60MPH, the engine might not produce enough power @ 1800RPM to push the vehicle through the air at that speed. IOW, RWHP could be less than road HP. Someone more motivated than me can get the calculator out and figger out the RWHP @1800RPM.
I got my best ever mileage driving from Spokane to Everett on HWY 2. Topped off in Airway Heights and when I filled up and did the math at the 76 in Leavenworth it came out to 17.0 MPG. Majority of the trip was very easy hills and a steady 65 MPH.
I don't think that I could get 13 mpg with my rig on the back of a flat bed.
Is there any technical reason why outside air temp would affect mpg? The best milage I've ever gotten in my 60 was 18mpg. I managed that several times on trips up/down I-5 to Portland or Vancouver from Seattle. Relatively flat trip, with 33" MT tires, stock gearing except for the H55. Same trips same brand of fuel, similar traffic, I've seen as much as 3-4 mpg variance depending on the temperature. If the OSA temp is between 55-65 my 60 just purrs, gets great mileage (for a 60!) and generally is pretty happy. If it is colder than 45 deg, it runs like crap and mpg drops significantly. Conversely, if it gets warmer than about 75, same symptoms.
I understand you get better/different combustion with different air temps, but I wouldn't think it would have that big of an effect.
Am I crazy or is there something to this?
I understand you get better/different combustion with different air temps, but I wouldn't think it would have that big of an effect.
Am I crazy or is there something to this?
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FJ40Jim said:
Found this on google, from a posting by Willem-Jan Markerink...thread is
http://www.off-road.com/4x4web/tlcal/v3n1479.htm (gotta dig down a ways)
Basically, you want to set the engine up to run at the low point in its
BSFC (brake specific fuel consumption) curve at your intended cruising
speed, assuming it has enough power to do so. This means gearing
adjustment. Ono the 2F it appears to be at about 1600rpm or so, right
near/at the torque peak. Problem is you only have about 55hp available at
that engine speed from a stock engine. (Note, the Specter catalog has the
bsfc curve for the 2F in it, though it is in metric it gets the estimates I
need. I think the older one had more curves in it.) Enter the RV cam and
small-tube headers and free-flowing but not huge exhaust system and a nice
tall overdrive gear. I'd be very interested in seeing what this sort of
setup can do.
Great thread...
Jim, any idea where the BSFC curve is for a 3FE?
Jim, any idea where the BSFC curve is for a 3FE?
