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| Mileage calculations | |
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| Tweet Topic Started: Aug 30 2015, 11:05 AM (604 Views) | |
| SteveK | Aug 30 2015, 11:05 AM Post #1 |
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Old time, I just found a previous reference to mileage and cruising calculations you did in 2012....for a 2WD SW with a F-134, T96-OD and 5.38 ratio,...
I have a 2WD Dj with L-134, T96-OD, and a 4.56 ratio Dana 23, and 29" tires. Could you show me the calculations you used, or please do them using my 4.56 ratio. Would the Dj be different than the SW by weight or shape characteristics? Thanks for any and all your expertise. |
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SteveK 62 Dispatcher South Florida | |
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| oldtime | Sep 1 2015, 11:40 AM Post #2 |
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Yes and no. Depends on what your calculating and the specific drivetrain components. The GVWR and aerodynamic drag will be different. The roll resistance and drivetrain friction may also be somewhat different. Those particular factors will only effect the fuel consumption and the operational efficiency. (overall cost per mile). MPG is mainly about Power vs. weight plus friction and drag. I will disregard your 2WD DJ reference because that is a reference to weight, friction and drag. I take the various figures that you have supplied and add a few other known facts concerning those various drivetrain components. I figure all this by a process that in general terms I call "AUTOMOTIVE RANGING". This topic of automotive "RANGING" consists of two parts. This incudes "ENGINE" ranging" and also "GEAR" ranging". The engine specifications are of paramount importance. That's because the engine specifications along with model selection plus intended use-age will determine the desired gearing. The F-134 specifications are not the same as the L-134. So first I take a look at known facts concerning the L-134 Go-Devil. As you know the crankshaft velocity of an automotive engine "ranges". The Go Devil crankshaft velocity ranges anywhere from 550 rpm at idle to 4000 which is the maximum achievable RPM in non modified form. The dynamometer chart shows that it puts out "Maximum Torque" of 105 foot pounds at 2000 RPM. RPM at maximum torque output directly correlates as the "maximum efficient RPM". Excepting wind drag, the "best operating MPG" will occur at 2000 RPM. The maximum sustained RPM for the L-134 is 4000. At 4000 RPM the L-134 will have a shortened service life. The "optimum sustained RPM" is a compromise RPM for any particular engine. The "optimum sustained RPM" is merely a suggestion based on RPM capability vs. engine service life. This roughly equals the "best sustained cruising speed" terms used in my earlier quote. I figure the optimum sustained RPM to be 2700. The dynomomeeter chart shows that the torque output at 2700 RPM is still within 5% of its maximum. The service life decreases proportionate to the RPM. So we strive to keep the RPM as low as possible while producing a reasonable amount of power. The achieved speed values are merely an exercise in math. The basic formula that I consistently use is.... CRANKSHAFT RPM ~ TRANSMISSION GEAR ~ OVERDRIVE ~ TRANSFER CASE RATIO X PINION GEAR ~ RING GEAR X TIRE CIRCUMFERENCE (diameter x pi) X .97 (average tire radius reduction due to load) ~ 63360 (inches per mile) X 60 (minutes per hour) = SPEED (noted as MPH)
Best efficiency should be 52 MPH. Above speed does not include air drag. HP is no doubt insufficient to overcome the increasing air drag but the sustained cruise is geared to run 71 MPH. Personally I feel that 4.88 FDR would be much more appropriate because the engine output will be hard pressed to maintain more than 62 mph on mildly rolling interstate. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| SteveK | Sep 3 2015, 07:03 AM Post #3 |
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OT, Thank you for your time and opinion. When you disregarded the mass difference of the larger, and wider and taller 3000# vehicle compared to a smaller 1800# Dj, it kinda defeated my purpose in asking for the calculations. Given the above, I can't buy into your results. With everything being the same in your formula, except for the new taller FGR, how did the lower RPM also end up with a lower MPH efficiency and cruising speed? I can guess two possibilities without the benefit of seeing your actual calculations. My best guess is you did not use .7 final trans DR of my T96-OD (50 Jeepster Borg Warner R10). Another possibility is, you show 6330"/mile when actually it should be 63360. That may just be a typo there and not what you actually used in your calculations. My Dj is most likely never going to be challenged with rock climbing bigger than the gravel between the road and shoreline, and inclines steeper than a parking garage ramp or expressway flyover. It's a cruiser for around Flat Florida. I was just trying to get some expectations of what kind of mileage potential and motor saving speeds I could look forward to trying to keep from getting run over on the expressways around here (posted Min 45MPH). Thanks very much for your time and always your unique qualified experience and knowledge of ALL the Willys and other things too. I enjoy reading the different conversations involved in both the Dj and 3B BB's. Thank you, and Derek too, as well as other members, for the contributions and shares of first hand knowledge. It has educated me tremendously and prevented a lot of potential errors. Thanks! |
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SteveK 62 Dispatcher South Florida | |
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| oldtime | Sep 3 2015, 07:17 PM Post #4 |
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The 6330 number was a merely a typo so I will edit out that mistake. Sorry, I've been way too busy with other concerns this past week. I did not figure yours with .7 overdrive. But now I see you wrote it down as T96-0D. I will correct the speed calculations given on my previous post. Thanks for mentioning those 2 errors. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| SteveK | Sep 4 2015, 07:06 AM Post #5 |
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OT, Thanks again for your time and calculations. I didn't mean to add to your already busy schedule. I see you edited above other things too. Your results now agree with mine on the pure RPM related calculations (BTW, I have a earlier post on that subject and access to that simplified formula). Quite frankly, when I read your use of the term "velocity" back in 2012, I guess I was hoping for some real life impacts based on the box shaped characteristics and weight of both Willys. I understand that would be very difficult to calculate. You just seem to have so much technical information available to you, that I thought "just maybe". As for the 71MPH cruising speed, there are a lot more than HP issues there preventing that, primarily ME not wanting to try to experiment with other drivers and conditions in a short wheelbase high center of gravity open vehicle. We all saw what happen to Glenn at 30 MPH. 50-55MPH expressway speed with everyone going in the same direction without intersections, is about all I'm willing to risk, and it is comforting to verify that that should be right at maximum capabilities and efficiency for both of us (me and the Go Devil). Thanks again for your time and expertise. I hope you have a good and safe Labor Day weekend, and everyone else does too. |
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SteveK 62 Dispatcher South Florida | |
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| oldtime | Sep 4 2015, 09:53 AM Post #6 |
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Well I suppose like an engine it may be better for a person to be a little too busy than to sit idle. I had been at "maximum cruise" for the past two weeks and I'm slowly getting back to the "optimum sustained" work load. "Velocity" is a term used in physics to describe motion. It is somewhat comparable to the term "speed". Speed is correctly used to describe straight line motion whereas velocity always follows some form of curve. The F-134 when installed into a universal type jeep and correctly geared is ideal for speeds up to around 62 mph. Also IMHO the stock CJ begins to handle poorly at speeds beyond 62 MPH. Note I'm not stating that the F-134 is the optimum engine for a universal type jeep. The dynamometer charts and my personal experience with a stock L-134 is that they have about 10% less available torque than the stock F-134. I find that the L-134 like the F-134 has a sustained engine cruise velocity near 2700 RPM. I have experimented with optimum ranging of the F-134 powered CJ-3B's. When ranging the CJ-3B I find the horsepower (HP) to be sufficient for use with a compounded final drive ratio (FDR) of 4.03 and no higher. 5.38 differential ratio times 25% O.D. equals 4.03 compounded FDR. 4.88 differential ratio times 25% O.D. equals poor performance. Considering all the Dana differential ratios that are available I claim that 5.38 with 25% O.D. is the absolute optimum gearing for the F-134 engine. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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