| Author | Message | ||
| Jim Huskins (Lostranger)
Registered Member Username: Lostranger Post Number: 15 Registered: 8-2007 Posted From: 68.238.120.80 Rating: N/A |
FAST FRED said: "The latest thinking in 80,000lb trucks is a 2.64 rear so no power loosing OD is needed. Top gear is straight thru , most efficient." This is great info, but it raises several questions: First, I'm not so sure five or six speeds IS enough in the mountains that are part of my daily life. I've never driven a manual trans coach that seemed to have a low enough first. Not going to an OD makes sense to me, but that leads to my second question. Will I need to change my R&P to 2.64? That's an expense I was not planning but need to know more about. Maybe I should go with a 9 or 10 speed Road Ranger without OD and change the R&P. Thanks for the brain fodder, Fred. I love this board. Can't believe I was off for so long. Jim | ||
| Kent Widdison (Kwidd)
Registered Member Username: Kwidd Post Number: 8 Registered: 7-2006 Posted From: 97.117.120.169 Rating: N/A |
I run a 2.64 gear in my bus but I have an allison 5 speed in it. I wasn't sure how good it would pull taking off in the mountians but I'm satisfied with it. I live at 4200 ft. and it is uphill to get out. We just got back from a short trip to southern Utah some passes at 9000 ft. It cruises at 1500 rpms at 65 mph. | ||
| Jim Huskins (Lostranger)
Registered Member Username: Lostranger Post Number: 16 Registered: 8-2007 Posted From: 68.238.120.80 Rating: N/A |
World of difference between an auto and a manual, Kwidd. When you're pulling out up a grade, that torque converter will slip and effectively give you a lower gear. Not so with a manual. If you get slipping, you're burning an expensive clutch. I believe I need something lower than a standard Spicer or Fuller. Glad to hear that the 2.64 works for you. I guess I'll have to plan for that swap. Don't yet know what's in the bus I'm trying to buy. | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1021 Registered: 8-2006 Posted From: 99.29.76.171 Rating: N/A |
Whats more important here is what is not being said, and hasn't been successfully enjoyed yet. The horsepower curve on both the S60-50 and the 71-92 series increases up to maximum governed speed. The torque curve rises until 12 or 13 hundred, and then decreases above that. The fuel consumption curve is best about 16-1700 rpm. So, we want to run the engine most of the time in the best of the three points. A 71-92 series won't produce enough horsepower at 1500 rpm to do much cruising at 65 mph. The drivability of a bus in the mountains geared for 1500 rpm at 65 mph will be non-existant. It won't go 65 into a 10 mph head wind in high gear, and it won't accelerate well in city traffic. Gear it for about 1800 at 65, and its a whole different bus. It will stay in high with an auto, accelerate from a stop, and its still at the top of the fuel consumption curve. I don't like running an engine against a governor either, the fuel economy goes way down. G | ||
| Jim Huskins (Lostranger)
Registered Member Username: Lostranger Post Number: 17 Registered: 8-2007 Posted From: 68.238.120.80 Rating: N/A |
So far, this discussion has me thinking that my original plan of using a 13 speed OD Road Ranger was right. I won't have to use the lowest gears when I don't need them, and I can always run straight thru on the top end unless and until I need a little over drive. That should give the Series 50 a happy place to live under all circumstances, and I certainly don't mind clutching and shifting. Jim | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 1186 Registered: 10-2006 Posted From: 76.248.150.30  Rating: N/A |
Remenber the 4 strokes are torque beasts unlike ANY of the two strokes. The old 2 stroke thinking < run it as if you want to KILL it, be on the gov most of the time , does NOT work for the 4 strokes, Most are driven by watching the boost meter and perhaps EGT . A Hound set the Sportscar up for 1650rpm at 62, most folks go to 1950 at the top of the good fuel burn point. The Ser 50 will do great at 1300 almost 50% fewer RPM at cruise. What works on a 2 stroke , has no validity on a 4 stroke. To get the best fuel consumption on the flats , indeed a downshift will be required for a grade. Hoe steep a grade is the question. We are hoping the light weight and small frontal area of the VL will allow a 3% grade at speed (70). The ZF has OD (with 2.93 rear) so if it kicks into 4th on a just a 2% grade , its fine with me , the game is easy fast drive ability. When completed we will play with tire size to optimize the flat vs hills issues , as the difference between 12R22.5 and 22,5 low profile in revolutions per mile is HUGE! Remember the sleeker and lighter the coach is , the more you are on unknown territory, in terms of setting all the numbers. FF | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1865 Registered: 12-2000 Posted From: 174.91.147.113  Rating: N/A |
A general word of caution for the novice in all thoughts about "4-stroke" engines. One MUST know the exacting details of the engine in question. The "best RPMs" differ from year to year, model to model, programming to programming and manufacturer to manufacturer. Here in North America, we have had major engine behavior changes due to emissions regulations in 2003, 2007 and 2010. The progression of electronic engine controls prior to 2003, makes each upgrade of those systems a game changer as well. Even within engine families over that time, the "sweet spot" has moved by several hundred RPM. Depending on the engine, running it a few hundred RPM away from the sweet spot will give you typical 2-stroke fuel economy.... The more gears, the closer to the sweet spot you can keep the engine, the better the performance and the fuel economy. With the way busnuts put things together, running what can be found, as opposed to ordering something specific, each of us will have somewhat unique engine performance criteria to plan a drive train around. All the more fun, says I!! happy coaching! buswarrior (Message edited by buswarrior on May 19, 2010) | ||
| John Wooldridge (Moovin_on)
Registered Member Username: Moovin_on Post Number: 2 Registered: 1-2010 Posted From: 148.63.184.62  Rating: N/A |
I am running a 10 spd roadranger w 0.75 OD with my series 50 and the 3.73 rear. Gives me plenty of grunt at low speeds and about 1300 rpm @ cruising speeds. Works well in mountains and is very reliable. Good fuel mileage too. John | ||
| joe padberg (Joemc7ab)
Registered Member Username: Joemc7ab Post Number: 424 Registered: 6-2004 Posted From: 66.38.159.33 Rating: N/A |
John Good fuel milage too. Do you have some figures you could share with us? | ||
| John Wooldridge (Moovin_on)
Registered Member Username: Moovin_on Post Number: 3 Registered: 1-2010 Posted From: 148.63.184.62 Rating: |
We did an 8500 mile tour of the US this fall. Got 9.6 towing. I get about 10 not towing, on average. Less if lots of mountains, but never less than 8.7. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 1187 Registered: 10-2006 Posted From: 76.248.150.30 Rating: N/A |
Here in North America, we have had major engine behavior changes due to emissions regulations in 2003, 2007 and 2010. The best by far solution is a PRE EGR , pre 2003 engine. Many small operators will pay extra for a nice older truck , and get EVERYTHING rebuilt. Costs less than a spanking new truck , is far easier to maintain and the fuel mileage is considerably better. We chose a '96 donor to avoid this hassle. FF | ||
| David Evans (Dmd)
Registered Member Username: Dmd Post Number: 461 Registered: 10-2004 Posted From: 173.77.207.138  Rating: N/A |
John, Wow! nice bus and great powerpack. Did you set this up? The 7 is a good looking rig also. Fred are you getting closer on yours? I know what your saying about the trucks, you cant pry some models away from the drivers. We are pleasantly suprised so far (5000 miles) fuel milage with the 6V71 and the allison, 8 to 10 mpg but 8.8 at 65mph on the flats. 3.73 rear. To get 10 i have to slow to 55 on the interstate which is ok, sometimes hard to do. We have a pretty slick airstream profile and 22,000lbs. Milage falls off towing and back roads and hills. | ||
| John Wooldridge (Moovin_on)
Registered Member Username: Moovin_on Post Number: 4 Registered: 1-2010 Posted From: 148.63.184.62 Rating: |
Thanks, David. A friend who is an expert mechanic (mostly him) and I set it up. It is a 94 engine from a Freightliner, 315 HP. Not the bus version, which is 275 HP. It is pre EGR. FF is correct that this engine gets better mileage. Good power too, but I had to learn to drive all over again after the 8-71. Characteristics are completely different. What would be lugging the 8-71 is what the S-50 likes. I tried to set it up for max fuel mileage. It weighs about 29000, runs 11R 24.5 tires to go with the .075 OD and 3.73 rear. I didn't want to go to the expense of changing the R&P, so compensated with the RTO tranny. It was cheaper that way. All major parts were used. The motor had 622K on it when we installed it back in 06. Now has 650K and has required nothing but routine maintenance. Who knows how many miles on the RTO. Another side benefit--no more cooling issues. John | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 217 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
2.64 ratio is good with a 9 or 10spd direct transmission. But-you are also restricted to 1550lb/ft torque on those boxes. We're (at Freightliner) gearing the trucks with 10spds with 3.42 ratios-which makes the final drive 2.49. With 13spds we're using 3.23 (2.36 final ratio) and with 18spds, since they have an extra low gear, 3.08 (2.25 ratio). Many tests have been done with direct drive transmissions with big gears (low numerically) comparing to overdrive transmissions. The biggest fuel mileage determinate is not whether or not the final drive is direct or an overdrive, but the loose nut behind the steering wheel. As stated, once you get above 1550lb/ft engine torque, you have to go with an overdrive transmission. Currently, Eaton has an 18spd in both manual and autoshift (with clutch pedal) that is rated at 2250lb/ft torque-of which there isn't an American made engine that will produce that. Detroit's DD16 and Cummins ISX both have 2050 ratings. Good Luck, TomC | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 218 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
Rpm's between 2 stroke and 4 stroke engines are basically the same-being rated at 2100 rpm. The difference is the sweet spot for running down the road. On a non turbo'd 71 series you want to be between 1800 and 2000 rpm. On turbo'd 2 strokes whether it be electronic or mechanical, best cruise is between 1600-1800 (including my Caterpillar 3406B mechanical with jacket water aftercooler). On early electronic 4 strokers, 1400-1600 is the sweet spot for cruising. Now with the new DD13, 15, 16 of Detroit, we want the cruise in the 1300-1500 range. But- the DD engines also have a 1100 rpm maximum torque with pulling down to 1000rpm OK. Horsepower is rated at 1800 with 2050 being top rpm. I've derated some fleets to maximum rpm at 1800, and the driver's don't complain. Now with the SCR (Selective Catalyst Reduction) or Urea (32% ammonia and filtered deionized water) exhaust injection, we're seeing fleets getting 7.2 mpg pulling 80,000lbs in regional market delivery, and over 8mpg on over the road trucks keeping the speed below 62mph. Imagine what kind of mileage we could get weighing less then 40,000lbs? This is the first time in history that the Diesel engines are getting better mileage with the new smog control technology. Granted you have to buy DEF (Diesel Exhaust Fluid-what they call the Urea mix). But-as FF says, stay with pre '98 engines for the best fuel mileage. After '98, practically each year took a mileage hit until the 2010 engines came out. Good Luck, TomC | ||
| Larry Baird (Airhog)
Registered Member Username: Airhog Post Number: 189 Registered: 1-2001 Posted From: 108.0.48.25  Rating: |
I have a 8V71T and an RTO in my MC-7 with the stock gears and 11R-24.5s. I get 15 MPG 7 around town (like I would drive it around town) and 8 on the road. At 33,000 lbs I am happy. most of my driving is between 70-75 and pulling a 6,000 lb. toad. I love my 10 speed and after having a 4 speed you couldn't give me anything less. I shift less and when I want I have the gear to run with the big dogs (on flat land) and I can make a new hound look like a puppy. |
