| Author | Message | ||
| Jim Sanders (Sandy)
Registered Member Username: Sandy Post Number: 66 Registered: 1-2011 Posted From: 69.199.96.250  Rating: N/A |
Hey guys I have been taught that a diesel eng should cruise as close to the peak torque range as possible???? Is this still true??? I am haveing to install a different rear end in my 68 flxliner. I will have it over hauled and checked out before i install it. If i have to change rear end rato do it now... COMMENTS NOW Please Jim | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1188 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
1300 to 1800 rpms work good for a 6v92 good luck | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 617 Registered: 10-2003 Posted From: 66.165.176.62  Rating: N/A |
Jim, Just wanted to let you know I'mnot ignoring your email about the rear framing I just haven't had a chance to go over and look at my bus yet Tim | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 309 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
92 series likes to cruise between 1500 and 1800. You can go a bit lower to 1300 if it is a DDEC engine. Good Luck, TomC | ||
| JC Alacoque (Jc_alacoque)
Registered Member Username: Jc_alacoque Post Number: 106 Registered: 7-2006 Posted From: 207.34.166.7 Rating: N/A |
Mine (6V92/HT740) revs about 2000 rpm at 60 mph, 2200 rpm at 65 mph. It has been doing that for about 200000 miles. It doesn't hurt it, it just burns more fuel. My 5C has the slower diff. If I found a high speed diff, I would swap. JC | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1260 Registered: 8-2006 Posted From: 99.37.28.23 Rating: N/A |
Sandy, What you are trying to come up with, is a roadworthy bus. One that will accelerate in city traffic, do fairly well on hills, and not scream and fry fuel at 65 MPH on the freeway, right? My suggestion would be to use the tire Rev-Per-Mile calculator available here, and come up with a differential ratio that will give you ABOUT 65-70 MPH at 1800 RPM. As you can see, the torque curve goes down with engine speed increase, and the horsepower curve goes up. The fuel efficiency curve is best at about 1500-1700 RPM, and lower above and below that. At 1300 RPM torque is high, but horsepower and fuel economy are low, best performance is at the highest torque and horsepower point. G | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 310 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
JC-yes it appears that it isn't hurting your 6V-92 to run it at 2000rpm cruising, but I doubt you'll get much more then 300,000mi out of your engine before overhaul. Running at a more reasonable 1600rpm cruise, 92 series should easily go 5-600,000 miles before overhaul. Personally-would never run a 92 series over 2100 continuously. A 71 series is very happy at 2300rpm though. Good Luck, TomC | ||
| JC Alacoque (Jc_alacoque)
Registered Member Username: Jc_alacoque Post Number: 107 Registered: 7-2006 Posted From: 207.34.166.7 Rating: N/A |
TomC, or anybody, can you explain why running a 6V92 at 2200 rpm continuously is bad. What parts of the engine would wear or break and why? The engine runs just as smooth at 2200 as it does at 1800 rpm. I replaced the crank and rod bearings last winter and I didn't see anything that would suffer at 2200 vs 1800. Is it something up in the pistons or the heads that matters? JC | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1263 Registered: 8-2006 Posted From: 99.37.28.23 Rating: |
JC, The problem is stress on the reciprocating parts, and increased wear between the pistons, rings, and cylinder walls. Hold one hand and arm straight out in front of you, make a fist, and move the fist up and down a foot or so, slowly. Now move the fist up and down as fast as you can comfortably, and notice how much more work it takes to do it fast. Your fist is the piston, your arm is the connecting rod, and your shoulder is the journal on the crankshaft. The wrist pin in the piston has to reverse the direction of the piston much more rapidly, the rod also has to change not only its own direction, but that of the piston, and the connecting rod journal has much more stress put on it to sling the rod around faster. There is also something to do with the speed pistons and rings move over cylinder liners. The faster the piston moves (in the middle of the stroke where the speed is fastest) the wear rate increases dramatically. That is why the 92 series has the same stroke as the 71, to keep the piston velocity down within limits, they just made the pistons and cylinders bigger. An overspeed failure is usualy catastrophic, a whole bunch of broken rods and pistons laying in a pan. On a separate subject, best fuel economy is acheived between ABOUT 1500-1700 RPM, and decreases above and below that. Best overall engine performance is in the top of the area where the horsepower and torque curves cross. G | ||
| JC Alacoque (Jc_alacoque)
Registered Member Username: Jc_alacoque Post Number: 108 Registered: 7-2006 Posted From: 207.34.166.7 Rating: N/A |
Thank you George, that makes sense. It is said that a 71 series is fine at 2300 rpm. And a 92 series at 2100 rpm. What is the difference? Is it just because the pistons being bigger, therefore heavier, there is more weight, therefore more wear on the wrist pins and journals and bearings? The bearings I took out of my engine at 200000 miles measured within specs and looked fine. I could've put them back in. The bus is been run at 2200 rpm all its life because of the gearing. I am not argueing, I am trying to learn from you more experienced people. Thanks again, JC | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 2103 Registered: 12-2000 Posted From: 174.89.174.139  Rating: N/A |
I'd be thinking that JC's '92, being lightly loaded, relatively speaking, isn't going to mind being spun a little faster than 2100? The advice about the '92 series being kept under 2100 rpm has come from the places where these engines were being worked hard. In busnut use, and installed in a flxliner with short gears, that engine doesn't know the meaning of work! happy coaching! buswarrior | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 314 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
Piston bore on a 71- 4.25". Piston bore on the 92- 4.85". The extra mass of the 92 piston makes for that much more weight to go up and down. It has been proven that 92 series don't like to go over 2100rpm for any period of time without the piston making an exit out the side of the block. If you changed the transmission to an overdrive-whether it be an Allison automatic or manual, with around a .74 overdrive-which is equal to 5th in the World transmission, your current 2200rpm cruise speed would drop to 1628rpm-which would be absolutely perfect for economical cruising. If you're planning to keep the bus for many more years, I'd seriously think about changing transmissions. Good Luck, TomC | ||
| JC Alacoque (Jc_alacoque)
Registered Member Username: Jc_alacoque Post Number: 109 Registered: 7-2006 Posted From: 207.34.166.7 Rating: N/A |
I presently have a 6V92 with HT740 in a 5C. Tom, is there an Allison with overdrive like you mention that would fit size wise? JC | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1193 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
JC, 2250rpm @ no load does not hurt a 92 series and be extra careful with the World Transmission you miss the gearing running in overdrive they will not oil or run cool any Allison dealer can give you the specs for the rpms a 4:10 rear is on the boarder line in 5th gear for a B500 or B400 A 3:36 is not hard to find for a 5 Global or Pro Gear has it in stock I had a 3:36 in my 5 from the factory (Message edited by luvrbus on July 17, 2011) | ||
| JC Alacoque (Jc_alacoque)
Registered Member Username: Jc_alacoque Post Number: 110 Registered: 7-2006 Posted From: 207.34.166.7 Rating: N/A |
Thanks Luvrbus, I will look for a 3.36 rear end. I am not worried so much about hurting the engine pushing it to 2200, but a faster rear end would give me better fuel mileage. Plus I could go fast if I wanted, LOL, JC | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1195 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
The 3:36 ratio makes a wicked 3rd gear on the 740 you will love that lol good luck |
