Cummings 450 performance

[Roverjohn]

How well does the Cummings 450 on a 2018 Allegro Bus do on 6% plus grades with small tow car?

[jcussen]

Depends on your total weight,  but if you have Allison 6 speed, would be happy with 45 mph in 3rd or 4th gear. Just remember to shift down till rpms are at 1800 or more to avoid overheating and you are still able to gain speed with more throttle.

[Twotoes]

I have an Itasca with a 450 Cummings and my friends have a new 2018 Allegro Bus. I can easily do 45 MPH and my friends say the same. 

[Barbaraok]

Just a little thing, but it is CUMMINS.   No 'g'.   We have a 350, and climb in 4th gear at 45 or so on 6% grades over several miles. Our mechanic is always  'downshift when you start climbing -keep the RPMS between 1800 and 2000, steady is how you want to go'.  

[FL-JOE]

I would suspect a late model 400 Cummins would perform almost the same.  I have never fallen below 45-50 on any grade so far.  Loaded coach is 38,540 and toad weighs 9,700.  Ours is 43' with tag.  

[jcussen]

https://prevostcommunity.com/PDF/Motor Home Fuel economy.pdf

Think this will help, meet a guy the other day that said his 40 ft coach pulling a suburban, could do 60 over Teton pass. I recommended a good speedo repair shop.

[2gypsies]

Our 40' motorhome had a baby 370 and we drove the western mountains all the time with no issues.

[Smitty77_7]

As mentioned, so much depends upon coach weights while traveling. If you run with a full tank of water (And some do, as it gives them peace of mind.), and you've just fully fueled up on Diesel and beverages of your choice ( :)! ) - then you will be going a bit slower up any hill you see. And as all mentioned, your eye's will see a hill as the grade increases, way before the engine and transmissions ECM's talk to each other and decide to downshift. The midsize block ISL, in a larger heavier coach application - very seldom rebuilds speed on a 6% grade, once speed is lost. So use your eye's and your brain, and downshift to keep the sweet spot for hill climbing. Our CAPS era ISL, which maybe the same engine 2gyspsies had in their Dutch Star, was a 370HP which Cummins then reprogrammed to the 400HP configuration for us. We have a Tag on our coach, so suspect we're 1200-1800 pounds heavier then 2gypsies were. And we too, have no real complaints about hill climbing with our rig. If I get stuck behind a few big trucks and lose RPM, well then I just tuck in line at take an extra few minutes climbing the hill:)! No worries on that part. 

I will say that their is a slight difference between the Common Rail Variable Geometry era ISL, that came out in 2004 (But 2004 as a cutover year, could easily have a CAPS era ISL - I know for sure, as we're CAPS:)!). The first ISL VGT's were also related at 400HP,  and the same pounds of torque as the CAPS 1200-1250 pounds ranges. But the VGT spools a bit faster, and has higher boost, then the caps ERA. Our CAPS ISL, 22-23PSI is pretty much max boost. I believe VGT ISL's , deepening upon year of engine 28-32PSI max ranges. The VGT does change the width of the HP/Torque curve, so you have more HP/Torque earlier RPM, and up to a bit higher RPM, before tapering back down. So a sweeter/broader HP/Torque curve helps in drivability of the engine. The ISL450, with added smog stuff, does also give you more HP then the earlier ISL400's. So that helps too, for hill climbing. 

One last comment when considering a coach that maybe used for larger amounts of mountain usage. Having a Compression Jake Brake, vs PAC or Exhaust Brake - does provide an added safety edge. I've always been more concerned, focused on, decent vs climbing mountains. So finding a coach with Jake Compression could be worth the extra costs, if you  plan on lots of mountain driving. 

Best of luck to you on your decision. Get it, and go have some fun:)!

Smitty

 

[Ray,IN]

On 9/22/2018 at 9:54 AM, jcussen said:

https://prevostcommunity.com/PDF/Motor Home Fuel economy.pdf

Think this will help, meet a guy the other day that said his 40 ft coach pulling a suburban, could do 60 over Teton pass. I recommended a good speedo repair shop.

Thanks for providing that link, it contains very useful information and rebuffs some old fireside stories.

[jcussen]

1 hour ago, Ray,IN said:

Thanks for providing that link, it contains very useful information and rebuffs some old fireside stories.

Yes, when driving barn doors, hp to weight is the key. My present 500 hp/1550 ft/lb torque, 42000 lb coach is not much faster than my last 300 hp/860 ft/lb torque 28000 lb coach.