If you're travel along a relatively flat U.S. highway or interstate - what gear do you typically drive?
I find 6th gear totally useless for our style traveling. The previous owner of our 42' 2002 U320 told me that the coach had a 'sweet spot' at 62 mph. Of course, I didn't believe him (he was older than me - wouldn't have believed him if he was younger than me either). After a couple of thousand miles, I found out that he was absolutely correct. My wife set that speed (62 mph) as the limit for my abilities, so if the road is relatively smooth, we drive 62. That means the ISM is turning 1500 rpm - so one might as well paraphrase that the previous owner meant to keep the ISM at 1500 (or little above). That mandates 5th gear for us. To run the engine 1500+ rpm in 6th gear is NOT a consideration.
Consequently, if we're on a 55 mph road, whether to be legal or to keep from beating the coach to death, means 4th gear in order to maintain 1500 rpm. At 1350 rpm and 55 mph, engine performance is dreary. At 1200 rpm, it's kind of like beating a dead mule.
My 36' U295, with a C8.3, never had these issues. With 5.13 gearing, it ran along spryly, at whatever RPM seemed to fit the scenario.
I sure would be interested hearing about your experience.
Larry
Which engine is in the U295? The torque curve of my 5.9L in-line 6 Cummins really does feel the same as the 251 Cu.In. inline-6 my Chrysler had, maximum torque at 1600 RPM.
Mechanical 8.3.
Check out the torque curve for your engine and run in what ever gear will keep you in the flat portion of the curve and at the speed you want. I have a CAT 3208T with an Allison 4 speed trany and my best cruising speed is 67 mph @ about 2300 rpm. I run this speed even if the speed limit is 80. For other speed limits, I run about 5mph under the limit for various reasons. Have a great day ---- Fritz
Torque curve peaks at 1200 rpm, but the engine can barely accelerate going down hill at that rpm. Anything below 1350 rpm is abysmal.
Cat 3176B here.....1500-1600 is the sweet spot...oh and that's 70mph
My 96 U295 cruises happily at 1750 rpm which is 63 mph in 6th gear in the Allison 3060R tranny (I think that's the model number). It is very happy at that pace, will climb hills effectively and ranges from 8.2 mpg up to 9 mpg depending upon topography while towing the Subaru.
Our 1995 U320 (400 hp/1350 lb-ft M11) seems to be happy in 6th gear on the freeway. I typically downshift manually only when descending steep grades. Otherwise I just let the Allison decide which gear it likes and I'm happy.
At what speed, David? And rpm?
At 70 MPH it's just over 1500 RPM. I haven't paid close attention at other speeds
My ISC 8.3 is happy at a 17-1800 you pick the gear 5th 58-60 or so 6th 65-68 or so.
Our Detroit turns 1700 rpm at 65.4 mph in 4th gear out of 4. Unless boring countryside, we usually cruise at 1600+ for a little better mileage. 4th gear is too short for the absolute best fuel mileage and would love to have the 6 speed and turn about 1500 at 65. No reason to spin it that fast but no 6 speeds were available for the torque in '93.
Pierce
My isl400 is happy in 6th at any speed 55 and above. I keep it in 6th except 5th in rolling hills.
My '99 won't go into 6th. until 62 mph makes towing in Cal. a pita.
my 96 is happy around 1650 and 70 ish mph. I keep it on cruise otherwise she wants to keep getting faster.
Larry
95' U280, C8..3 / 6 speed running Michelin 275 80 22.5 XZE - LRH......... 75 psi front ....85 psi rear (cold)
6th gear @ 1700-1800 rpm ........ 60 - 65 mph verified by Garmin ....... using cruise control and "Mode On" in the non-hill country.
Average 10 - 10.5 mpg on our 3 trips out west from our home state of Florida (and I let it idle alot).
Using the "Mode" selection makes a big difference in the driving experience on our coach when traveling in flat country or rolling hills and interstate overpasses. The downshifting from 6th to 5th on overpasses and gentle hills was annoying while driving at speeds of less than 65 while in the default performance mode.
To answer the OP's question, always 6th gear unless mountain grades dictate otherwise......... ^.^d
Our '93 coach runs just like Justin's (above). Cruising on the highway, the sweet spot is 6th gear at 65 mph which is about 1800 rpm on the tach. Our transmission also defauts to "performance", so I turn "mode" on when driving in the flatlands and let engine torque do it's thing.
Unlike Justin, I actually like letting the Allison get a little exercise, so I take it out of "mode" when driving in the rolling hills. I like to feel the trans make the smooth down and up shifts as it sees fit, and I like the sound of the engine and turbo spinning up to 2300 rpm (we have a resonator). I also like keeping the revs up when climbing even moderate grades in the summertime, because it helps the engine run cooler.
Yes, I know...all the extra shifting burns a bit more diesel. I didn't buy a motorhome to go hypermiling.
I'm a retired toolmaker and one of the ways I annoyed my employers was questioning their orders. Why? Because sometimes they hadn't asked the correct question.
Larry, I wonder if you as a U295 Owner appreciate the difference between a 2-stroke and a 4-stroke engine.
A 2-stroke engine always gives you its best at higher rpms, whereas a 4-stroke engine can be designed either way, but 4-stroke diesels always develop their maximum torque at low rpms.
3-cylinder, 2-stroke Saab being flogged for all she's worth.
Saab 96 2-stroke singing - YouTube (https://youtu.be/dXVRdSbKDT8)
So. What is the operational difference between a 2-stroke Detroit Diesel and all the others?
My little U-240 has a Cat 3116 250hp with Allison MD3060R. It runs best at 2200rpm 6th gear doing 68mph. My limiting factor is the towing of the 11 chevy HHR is 65mph and we always tow it. So we cruise in 6th gear at 2000rpm doing 64mph on flat level ground getting 9.5 mpg.
I've read that the best way to drive a Detroit 2-stroke is to "drive it like you stole it." That high-RPM operation seemed to work well with the 8V-71 engine in the MC-5 coach I used to drive for our church. Our Cummins M11 is much different in that it's quite happy at lower RPM as I let the Allison decide which gear it prefers.
D.J. Osborn? I still don't know if U295 owner's rig is a Detroit or some other engine. I was suggesting the question that Larry should have asked in my humble opinion.
Vintage Saab Two Stroke Race Car with Crazy Swede Driving. - YouTube (https://youtu.be/jW0gdelW3dY)
Actually had a Saab 96 back in the day, shocked a lot people at gas stations, when I poured a quart of two stroke oil into the gas tank.
Thank Pierce. I've always been fascinated with 2-strokes, and our U225 is probably our forever home so I won't experience the Detroit. That being said I went back to the beginning, and remember why I don't trust my memory or as Lynn puts it to me "The mind is the last to know."
Larry wrote "That means the ISM is turning 1500 rpm - so one might as well paraphrase that the previous owner meant to keep the ISM at 1500 (or little above). That mandates 5th gear for us. To run the engine 1500+ rpm in 6th gear is NOT a consideration."
So he's driving a 4-stroke. So my answer to U295 Owner Larry is to remind him why trucks have all of those gear ratios to choose from: to be able to run the engine at it's best speed. Larry? Run in the gear that gives you the engine speed you want.
I enjoy your writing on the Detroit 2-stroke Pierce. Many of them travel the highway here bringing farm good to market. Then WalMart truck goes by with the driver hypermiling.
"A video of a walk around the running Sulzer/Wärtsilä 12RTA96C main engine on board the Maersk Kimi, currently at 70 revolutions per minute. It is the world's most powerful reciprocating engine to date."
"Wärtsilä-Sulzer RTA96-C. The Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä. ... The design is similar to the older RTA96C engine, but with common rail technology (in place of traditional camshaft, chain gear, fuel pump and hydraulic actuator systems)."
Sulzer 12RTA96C: a walk around world's most powerful reciprocating engine,... (https://youtu.be/awJIvdzL5dE)
Art
P.S. Waiting for my back to recover and enough enforced rest so that I can install the last three bolts in the Siata's new exhaust system.
That's what helped discourage people from owning the 2-strokes in New England: the availability of 2-stroke oil. People would pour in regular motor oil, as a substitute, in the winter time and it would just sit on the bottom of the tank.
::) This thread is very off-putting. In a previous thread, OP, U295OWNER stated that he has not changed his user name, even though he has sold his U295 and currently owns a 2002 42' U320 with ISM power.
So, if the original question asks what gear do you drive on the interstate in your 2002 U320, earlier answers won't help you much.
But on freeways, 95% of the time, I drive my 2001 U320, ISM, in 6th gear, econ mode, at 65-67mph, around 1450RPM, in the peak of the torque curve, and get 8.4mpg pulling a toad. Faster/headwind=lower MPG due to parasite drag mostly. With a tailwind, I will go 70ish.
You need to be above 60mph without full pedal for the Allison to shift to 6th gear. If you drive at PO's 62 sweet spot, in 6th gear, RPM will be lower and not at peak torque, but you'll have better fuel economy as long as the turbo isn't screaming (turbo pressure is what I use to approximate MPG...high turbo pressue = low MPG). Any RPM above 1450 will give you more horsepower and burn more fuel. In hilly terrain, I deselect Econ mode for quicker downshifts, and that keeps the speed up on the uphill pulls and increases cooling to engine and transmission.
U295OWNER, to avoid confusion, you really need to change your user name, or add a signature line to your profile stating what model coach you have.
I strongly agree that a name change is in order to avoid confusion!
So the 2002 U320 came with the Cummins ISM-450 electronic diesel engine and the Allison 4000 MH 6-speed transmission with the Allison transmission retarder (dualactuated.)
My 1992 U225 came with the Cummins 5.9 inline-6 and an Allison Mt-643 four speed with lockup in 3rd and 4th. So at the end of the day I drive at the speed that gives me the RPM I need, the same as my 1950 Chrysler. In the case of our GrandVilla, 62 MPH gives the engine 2,000 rpm and that feels good to me. Anything higher feels rushed. The SIATA restoration is holding up travel plans, but the end is in sight!
Art
P.S. 45-50 mph was the best speed for the Chrysler in direct drive for economy.
PPS My 1983 Honda V45 motorcycle? On a long drive to go pickup something small, if traffic encourages I have no problem with 8,000 RPM and "ahem" MPG riding with traffic.
The SIATA restoration is holding up travel plans, but the end is in sight!
Art
I know what you mean about the perfect speed for the highway. Anything above does not feel right with some engines or driveline configurations. My Ford 7.3 mechanical turbo conversion was like that. Great engine with lots of low end power but never felt good at higher RPMs. It was on a Dodge chassis but even with an overdrive on the Getrag manual 5 speed, I was in 5th on a freeway on ramp by the time I got to the freeway. Nice to have a good low numerical final drive option. Only the latest automatics give economy priority for freeway driving and can split shift to make the best use of the engine. With a good ratio, the Allison 6 speed is excellent for squeezing the last MPG on the freeway. Wish we had one.
I just built a wooden gantry crane from internet plans. Perfect for Fiat toad engine installations. I changed it slightly and have a 1500 lb electric winch instead of the chain. Total is just under $200 including the new electric winch. See YouTube below.
https://www.youtube.com/watch?v=PtPU1pOTLH4
Pierce, Gaylie and Koda wrote: "I just built a wooden gantry crane from internet plans. Perfect for Fiat toad engine installations."
The Wanderlodge have a hinged radiator option. My U225, lots of bolts. The Siata? Built on the Fiat 850 chassis, the rear sheet metal comes out with a handful of votes. You can roll the drive line out on a floor jack. Just like a motorcycle
If yours is a 36' model, how did you squeeze 1,140 watts of solar on the roof?
They fit but not much space left over. Craneman has five up top but is a 40. Photo below shows all four panels. 72"x39" as I remember.
Anyone figure how to get the Allison to shift into the next gear at a lower speed? I would like to loaf along in a higher gear at a lower speed. Nice to have the tranny computer figure the engine load and then shift so you could not run high EGTs but could ghost along in a higher gear at low throttle position. Just like a manual transmission.
Pierce
Is the U300 a widebody or old school standard width?
Not to be insulting but have you tried taking your foot off the foot feed? If yes, than how about asking Allison if they can adjust some parameters in the control computer?
With a "throttle" cable giving a mechanical transmission load information you can choose to give up foot feed down shifts for an earlier up-shift. I'm a ghosting along kind of guy. We drove across Fort Stewart recently and it was a pleasant drive (sort of) ghosting along at 55.
I don't have the Pro-Link 9000 cartridge for Allison transmissions. I know they make a cartridge for the 6 speed World Transmission. Link to an example: https://aepsurplus.com/custom/auctionArchiveDetail.cfm?aID=1198 Cartridges for the ABS are also available.
It's 102 inches. They fit well but the aluminum roof rails would be in the way on the 96 inch in the right rear. Commercial panels are 77"x 39." I installed these many years ago. Today, with better efficiency the panels would produce 1300 watts or more.
Pierce
Craneman our 97 goes into 6th at 55 exactly unless floored.
No idea if that's normal or just changed
One of ours must have been reprogrammed. Would need some coaches of the same model to compare to find out which one.
As I recall when I had our Allison ECU reprogrammed many years ago by an Allison dealer is that you can change the upshift points in 100 RPM increments. That would need to be confirmed for different series of ECU's.
Shift points MAY be able to be lowered, but you would need to verify that lowering it would not allow for the engine to be at high throttle positions at RPM below PEAK TORQUE RPM for your engine (each engine family is different-- the larger the engine, the lower the peak torque RPM.
Craneman the torque/hp curve on mine is so flat that raising the upshift points would seem to make little difference. The torque is slightly more speedy than revving the motor and using more of the hp part of the power curve.
Only difference may be fuel mileage? Maybe I'm mistaken. Might be a better drive with higher upshift points but I doubt it
On my coach I can't get into 6th gear until I exceed 62mph, but then I can ease back to 60.5mph and the tranny will hold in 6th. That's the slowest I can go without it dropping back to 5th.
Pierce
Do you use microinverters on each panel or just maintain a battery bank?
6" makes a big difference.
My motorcycle(s) have a 6-speed, and I shift into 6th at 60 mph and cruise at 4,000 rpm.
Art
On the interstate we run the M11 in 6th gear with the mode switch on and cruise set to 62 mph. We allow the Allison to due it's thing. It usually maintains the engine between 1400-1500 rpm depending on the roads. When on hilly grades and backroads we focus on maintaining the engine at around 1500 rpm through manual shifting.
John M.
One Midnite Classic 150. Yes, a lot more thought involved if 96 inches. Could use other type panels instead of commercial.
P
On this Alaska trip which will total over 12,000 miles I drove with the mode switch on (economy) and my speeds varied from 40 to 64 max, and lots at 50-55mph. At 50-55 I was in 5th gear and averaging around 1250 to 1350 rpms. At 62+ I was in 6th gear at about the same rpms. My fuel mileage averaged about 8.5 mpg. Interestingly it was about the same at the slower speed, probably due to not pushing the air as hard. This is with towing our full-size truck, about 6500# loaded.
When I would drive at 60 mph I would speed up to 62 and once it shifted to 6th gear I'd slow back down to 60. Worked fine until I hit a hill and it would downshift to 5th.
Looks like mine is the norm. I can get into 6th at 62 on econo and back down to 60.5 and keep in 6th as long as no throttle input from the cruise or me.
Great info. I like the idea that someone along the line of owners or new changed mine to upshift at 55.
ESPECIALLY now that the changes I have done make the torque aspect at lower rpms much much more noticeable.
The stock setup seems to use the hp side of the engines power curve. Mine downshifted under throttle application like you are all mentioning.
Yet was set for 55 into 6th.
Changing the motors response now matches the trans upshift pattern very well. Before the mods, no.
Donaldson blue tech, aero 50/50 xl resonator, dynamatics 199 degree fan controller, new alternator, valve adjustment, enough solar to run the coach after batteries reach 100%, lower rolling resistance tires, correct tire pressure for weight.
If I could stand to do it our 97 at 62 mph would average closer to 10 mpg.
I just did not like the revvy motor. Not right compared to what I had experienced driving countless other rv's.
Still slowly builds speed up medium grades in top gear.
Slight grades holds cruise speed fine.
Interesting that mine was modded somewhere along the line.
The resonator, fan control and the tires low rolling resistance made the most differences in that order in my opinion.
With the Michelin Xza-2's if I backed off the throttle the coach slowed in traffic noticeably. With the Xza-3+'s you have to use the retarder or brakes in traffic. That noticeable. Plus syn oil in the hubs and trans.
Paid dearly for the Cummins shops guy to weld up a beautiful flowed exhaust system.
All to get the motor to torque versus downshift and rev.
Now if I was ever in Pittsburg, Pa. I would let Pittsburg Power have a few days to look at the engine "just to see if everything's ok." They suggested on their web site the less restrictive air filter.
Fast cycling air pressure is also a power loss.
Still not as fast as others I have driven but much better and does even better with the lower upshift points it is set for.
May Dyno the coach just to see. If more power is available it's a good thing.
Tool.
The 643 should have a cable. Loosen it to increase the kick down point. Maybe it will upshift sooner. Mine does. Shifts the same at wot
Mike! I'm 63 years old and I've been messing with machinery all my life. One of the first things I did was slide underneath and check stuff out. In my case I looked at the condition of the transmission throttle cable and said to myself "Let's let sleeping dogs lie."
In any case this old bus hasn't told me everything it has to tell just by driving and listening.
Art
There can't possibly be a correct answer here as there are too many variables to be evaluated I just run where the engine wants to run, push on the peddle in a smooth linear motion allowing it to gain rpm, glance for any wisps of black smoke in the exhaust stream. Even with a four speed I rarely shift down. Don't use the cruise control, and heck I have never even tried it on my coach, because past diesel experience has been that they overreact.
Fred, I don't have a clue how other FT engine combos run, but my U320 ISM cruise control is spot on, dead accurate, with zero wander on the flats. I kick it off in the mountains tho. Woody.
My cruise control also is spot on. I use it as much as conditions permit. If it's hilly, I often drop it into 5th so I have some engine braking on downhill runs. Otherwise I'll get going faster than I want, and use of the retarder will kick it out of cruise.
Tom my cruise works with the retarder and does not kick it off.
Tom, c'mon, you mean to tell me that on roller coaster roads that give and take you don't ever leave you feet flat on the floor, raise your hands over your head and shout Wheee ! as you rig gains speed on the downhill side while the sensible part of you calculates how far you'll be up the next rise before you come down to the speed limit?
Old Phart Fred, I have the MT 643 and the Bendix cruise control and it seems to work just fine, now that I'm getting used to it's operation and the switches have awakened from their long sleep. Feels the same as the cruise control on all of my 70s, 80s, and 90s Chrysler products.
No, not so much feet on the floor "wheee" on the downhills for me.
My toad is an MDX. Not only is it limited to 65mph while being towed, I know the tranny is it's only weakness. The transmission fluid turns dark after being towed, darker after being towed too fast. I change the transmission fluid after every long trip, and this car with nearly 200000 miles has no issues.
When traveling in California, the speed limit while towing is 55. I keep the cruise set to 60-62. Very little "wheee" before the MDX limit.
When traveling out of state or out of country, I keep it right at the posted limit. I don't want a visit before the local magistrate.
Better safe than sorry. Plenty of fun awaits me outside the wheee experience.
I use the cruise control on our 1995 U320 nearly all of the time unless in congested traffic or climbing and descending steep hills. It works perfectly and makes the driving experience far more pleasant.
The tires on my trailer are approaching their age limit, so I understand.
Once, on a weekend trip to Montreal for food and drink, I left the cruise control on my Caprice Classic Estate Wagon set on 100 KPH while forgetting to tell my passengers that it was kph. As one of them nervously looked out the window for police helicopters, and the others imagines what an international speeding ticket would entail, 3 or 4 Ford Mustangs with US plates whizzed by us as if we were standing still. I imagined that as typical Americas they didn't understand that other countries might not use "miles." At the toll booth the cars were parked, the drivers were in restraints and I paid my toll and motored on.
There are interstates in Vermont, Pennsylvania and Virginia however . . .
Paid more attention today in a drive up from San Diego to our San Juan Capistrano home regarding the upshift points.
More throttle extends the upshift rpms in all the gears until the 55mph upshift into 6th.
Unless floored 55 is it.
Driving in traffic with the "mode" on the coach pulls from 55 on up without downshifting. Mode off will downshift if aggressive enough.
Having it not upshift until 62 and then downshift then upshift readily would not be my personal choice.
The trans seems to react to the available power going into it. In other words if the engine is struggling to maintain speed up a grade it will finally downshift even with the mode on.
Fairly gentle grades over 55mph the engine will take full throttle and not downshift as long as it's gaining speed.
The lower parasitic power losses and the other changes really work well with the 55 into 6th setup.
I run 64ish in 6th gear @ 1400ish RPM in most cases. I can't even get into 6th unless I am above 61mph. I use cruise control most time, but keep it in economy mode. Most times it doesn't downshift and I don't believe I am "lugging" the engine. It will go up a pretty good hill without slowing down enough to downshift.
I've found that running this way offers the best fuel economy. If I am quick to downshift to 5th or have to run in 5th due to a 55mph speed limit, fuel economy is noticeably worse.
I sometimes wonder how it would do at 70-75mph.
I noticed temps as high as 188 or so without downshifting on the VMspc which is higher than I remember on mostly flat ground but it was 98 outside and the radiator was dirty so I didn't worry much.