Setup to reach 9.66 MPG at 65 MPH ?

[someguy]

MCI advertises that a J4500 gets 9.66 MPG at a steady 65 MPH in independent testing.  Perfect conditions probably, but it still does it.

See item #3 on page 18 of the attached brochure.

The interesting thing about that claim is that MCI doesn't offer the AS Tronic transmission anymore, only the Allison "Gen V" automatic.  So that fuel economy  was done with the Allison and the AS 12 is known to get a further 10% better fuel economy than the Allison.  A 10 MPG intercity bus ?

The brochure also says "Fuel economy optimized rear axle ratios delivering up to 19% better fuel economy in certain configurations" on page 25.

So how is MCI setting up these buses to get such good fuel economy ?  They are using the Cummins ISX12.   What RPM is the engine running at 65 MPH ?

[luvrbus]

Cummins developed the ISX 12 motor coach engine low horse power 385 t0 425 hp with high torque at low rpm's  Prevost is playing catch up using their D13 with electric fans and around 450 hp down from over 500 hp and they are a dog 

[someguy]

Cummins developed the ISX 12 motor coach engine low horse power 385 t0 425 hp with high torque at low rpm's  Prevost is playing catch up using their D13 with electric fans and around 450 hp down from over 500 hp and they are a dog

The new J4500 has electric fans too.

This guy is running a 500HP D13  and getting fantastic fuel economy.  >9 MPG on a lot of trips.  He shows the MPG indicated on the dash.  He says 8.5 MPG lifetime MPG running at the speed limit all the time.
https://www.youtube.com/watch?v=8uwc7F3ixpg

It can't be that gutless because he passes other trucks going up passes, while loaded to 72-80,000 pounds.  But low lugging engines feel gutless.

His truck has a 12 speed iShift.  It has 2 modes, economy and performance.  He uses performance when going up a pass.

I'm targeting a coach with the 12 speed AS Tronic and the ISM.  2nd choice is a DD S60.  Last choice is the Cat.  There were a ton of issue with the C12/13 in these buses.

[luvrbus]

Give me break I pushing a box down the road@ 48,000 lbs with a ISX 15, 650 hp and with the generator and Aqua.Hot I am at 7.3 mpg and sometimes I run 70 to 75 mph.The Jake brake is a marvel on the ISX 15 .Cummins upgraded me from 600 hp to 650 hp for better fuel mileage believe that or not and it worked   

[someguy]

Give me break I pushing a box down the road@ 48,000 lbs with a ISX 15, 650 hp and with the generator and Aqua.Hot I am at 7.3 mpg and sometimes I run 70 to 75 mph.The Jake brake is a marvel on the ISX 15 .Cummins upgraded me from 600 hp to 650 hp for better fuel mileage believe that or not and it worked   

What kind of bus do you have ?

All you have to do is look at the ECM on those engines.  They don't lie.  And the VNLs are very aerodynamic. 

Modern trucks are running direct drive transmissions so that there are no gears involved when cruising, along with a 2.60:1 axle ratio.  Which is like a 3.3:1 with an OD transmission.

I think the fastest axle ratio available for a J is a 3.36:1.

[luvrbus]

The Silver Leaf reads the ECM direct or like me it will calculate the gals used from the fuel tank when using the Aqua Hot and generator I am around 7.8 using just the ECM.I know a little about Volvo engines a friend in Phoenix owns the largest trucking co in the US and probably owns a thousand or more of Volvo trucks plus other brands,he owns Volvos with ISX 15 Cummins also along with the Internationals,Petes,and KW's in his fleet   

[buswarrior]

There's more to these fuel economy claims than just the choice of hardware.

The acceleration rate is controlled by the computer, not the driver's right foot.

So programmed, the Allison equipped will take just as long to reach highway speed as the AStronic, if not longer.

There's no high powered blast off and 9 mpg grouped together...

But at least it is smoother, no gear shifting pauses to tire out your seniors tour group, heads rocking back and forth constantly...

Read further, the direct drive choice also means heavier driveline parts, so the truck starts getting heavier in the pursuit of fuel economy. No free lunch...

Rpm is way down at 1100 give or take, at highway speed.

Downright spooky...

Happy coaching!
Buswarrior

[someguy]

Would you gear a S60 or ISM to cruise at 1100 RPM at 65 MPH ?  Or is that only applicable to the new wonder engines ? 

The 12 speed Astronic gear splits are 27-29% versus 34% for a standard 10 speed.  So even if top gear is super low RPM, the next gear down is 1400 RPM, which is still a reasonable cruising RPM.  The next gear down after that is 1800 RPM.  So you really have 3 gears to chose from to cruise at 65 MPH, if you set it up that way.

[sledhead]

my sweet spot on the cat 3406e is 1525 rpm and that is about 67 mph but most times I run at 62 mph . at this speed it makes most hills flat so I use cruise control a lot and at that speed my mileage is 7.9 -8.3 mpg  . but this is on a pre emission 1875 foot pounds of torque 550 hp engine 

dave

[buswarrior]

Very misunderstood in busnut circles is the progression of the engines through the various emmissions regimes.

Any particular engine, you have to know what it was designed for, and what rpm is intended to deliver the power and fuel economy compromise for the vehicle it is going in.

Truck guys generally don't know about buses either..

Knowing that engine is really important, for instance, some of the last Cat motors, if it was run as little as 100 rpm away from the magic rpm, the fuel consumption curve was "V" shaped, and would bankrupt the fuel budget.

Generally speaking, the older it is, the faster it spins, the newer it is, the slower it may be spun.

Also, the whole Allison transmission thing will bite busnuts hard in the future. Just buying a "B500" or "4060" off someone cheap...They are not all capable of aggressive downspeeding, a whole ton (maybe 2 decades decade's worth?) of them can't spin below 14xx rpm, the lube pump in them was never intended to maintain it at cruise any slower. Lets be fair, cruising at 1500 was quite magical back in the day...

So, you have to have the right Allison to match the right engine.

Lots of research of information not readily avialable anywhere but a grizzled veteran at the manufacturer.

Happy coaching!
Buswarrior

[Jim Blackwood]

So what would be the most efficient cruise speed for a '96 DL then? (no tachometer)

Jim

[thomasinnv]

So what would be the most efficient cruise speed for a '96 DL then? (no tachometer)

Jim

Judging from my own personal experience, most efficient cruising speed depends on the terrain. I generally run at 65 which puts rpm right at 1550 which is just over the optimum rpm for the series 60. The series 60 likes 1200 to 1500 rpm for maximum torque output at best fuel economy. When in Commifornia I am limited to 55 because I tow. When on flatlands I may notice about 1mph better economy, but in the mountains it is worse. If I maintain 60 to 65 mph in the hills I actually see an improvement in economy over doing 55mph. So based on my experience it would seem that when lower power output is necessary to maintain speed, running lower in the torque curve seems to be the ticket. But when requiring maximum power to maintain speed it seems running closer to the top of the torque curve gets the result.

I would assume however that the same engine with different torque/hp setting may not observe the same result. I definately noticed a difference going from 370/1450 to the current 470/1550 setting. Flatland driving didn't change much but I did get a boost in economy in the hills.

[buswarrior]

So what would be the most efficient cruise speed for a '96 DL then? (no tachometer)

Jim

What engine version is in it?

You missed the point, it all depends on the particular engine that is in it. Could be a 95 or a 97 engine in a 96 coach... and as noted, what engine settings?

This is such a particular exercise, the advice for one thing will be completely the wrong advice for another.

The answer must be specific to your exact DNA, or you're wasting yer time.

And it was still popular back then to gear buses with 4.56 differentials for rocket ship top gear performance. The truck guys stare in disbelief, cuz a 4.56 gear at the time went into a tractor expected to gross 135 000 lbs...

A most hazardous area for casual answers, and whoever gives the advice has to know buses and their peculiarities.

And none of us drive far enough for these shades to make a difference. Leave the engine running while you fuel, and the savings from the weekend are gone...

Happy coaching!
Buswarrior

[luvrbus]

The generation 5 Allison is remarkable the driver or the engine cannot out smart one

[chessie4905]

That's how they get the reliability out of them now. Also the constant addition of additional speeds helps to use lighter and more compact components. The shock to the trans parts is much less in a 10 speed, compared to say, a 4 speed, since the rpm  change difference when shifting is is significantly less. Plus computer controlled clutch and torque converter apply.