When is 600HP not enough.

[tom chelbana]

Was talking to a Newmar Kountry Klub member at a rally last week,with a 15 Essex that had the 600Hp engine and was complaining that he was down to 30MPH on some 7% grades on Highway 154 in the Santa Barbara area and had to pull over because of his speed and the number of vehicle behind them. We traveled the same highway with our 18 LA with the 605 engine with same torque and was able to pull the hills at 45MPH. The difference was that he keep his trans in 6th gear and didn't shift down, and we downed gear between 3rd and 4th. A suggestion on long grades, it's a good idea to down gear and get your engine RPM up to 17 to 18 hundred range or a little higher. His trans wasn't down gearing low enough to keep his speed up and that was the reason his speed was so low. 600 HP is more then enough to keep your speed up on 7% grades. This would also be the thing to do on coaches no matter what engine they have. If you need to down gear to keep your speed up that is what you should do.

[Excesses]

When I saw the topic, I was thinking that maybe Elon Musk had become an RVer and was trying to launch one

[Lug_Nut]

He could not be still in 6th at 35 mph, whether allowing the transmission to shift or doing it manually. If his description is correct, he has an issue with his rig.

[TJ]

We travel a lot in the mountain west and I've learned to drive proactively so as not to get bogged down. They put those downshift buttons on the transmission for a reason and I use them to my advantage whenever possible.

And, when I see a steep grade approaching, I use that pedal under my right foot BEFORE the engine starts to lug down. Diesels like to run in a fairly narrow rpm range and anything you can do to keep them happy is to your advantage.

As for adding horsepower, when you start doing that, there's no end to it. Just ask any race car driver!

With motorhomes, it is mostly a matter of physics. We are trying to move a heavy object that also has significant wind resistance. As coaches get bigger (and are filled with more things), the weight goes up and the power requirement increases. So, 600 HP in a smaller, lighter coach such as a Ventana 3436 would really make it fly. Stick the same 600 HP in an Essex or King Aire loaded down with every convenience you can think of and you can get sluggish performance on occasion. It is the nature of the beast.

TJ

[Mr_D]

With my 650 Comeapart I find that 4th gear will pull pretty much anything and keep the speed up.
Now, if I had a 15,000# stacker behind me....

[Lug_Nut]

Jim, you are right in my opinion. Pretty well all the Newmar models are equipped with a similar power per pound configuration. I have owned and ISC @ 350 hp, an ISM @ 500 hp, and an ISX @ 600 hp. Each was sufficient for the GVW of that vehicle. The acceleration was about the same with all, except perhaps the ISX at higher speed acceleration. (ie: 60 to 70 plus MPH.

So, probably the engine you have in your rig model, is probably equal and just about right.

[Winepress]

Big RV’s and Hwy 154 = Not a good road choice, take 101, safer and more scenic.
The gear down part is all good.

[JFXG]

In general, 100 Lb/hp is the approximate design baseline. If you’re moving that or slightly less you ought to have no difficulty in most normal circumstances, (assuming you’ve learned a little something about operating a diesel. We can all learn more.). Substantially more weight, and you may find your coach running a little short of ooomph at high demand times.
Example: Loaded to travel, with toad, I’m right at 35K Lb. I have a Cat 330, so I’m moving about 106 Lb/hp. My Cat offers max torque @ 1450RPM, and max hp @~2100RPM. In cruise in open country I always use the CC and split the power difference, cruising at 1750-1800RPM. This gives me about 63-65Mph. On sustained upgrades I downshift to bring the RPM up to 2000 or so. This lets me keep about 50mph or so (as long as the grade is not too steep) and the higher RPM keeps the engine temp right where it belongs.

[BBelanger]

I plead guilty to not manually operating my transmission. I just keep the pedal to the metal or the cruise control on, and I pass tractor trailers going up hills. I figure everything must be working alright. Doesn’t the automatic transmission have all this stuff programmed properly?

[Stuart W]

Originally Posted by BBelanger

I plead guilty to not manually operating my transmission. I just keep the pedal to the metal or the cruise control on, and I pass tractor trailers going up hills. I figure everything must be working alright. Doesn’t the automatic transmission have all this stuff programmed properly?

I also have not down shifted yet, same as Bill “pedal to the metal” so far it’s worked fine, will have to try down shifting.

[FLJOE]

Originally Posted by BBelanger

I plead guilty to not manually operating my transmission. I just keep the pedal to the metal or the cruise control on, and I pass tractor trailers going up hills. I figure everything must be working alright. Doesn’t the automatic transmission have all this stuff programmed properly?

I'm with you. The only way I'm going to start manually selecting lower gears going up is if I have to let off the pedal getting hung up behind a slower moving vehicle. Then I probably would simply because once I push back down on the pedal it will downshift anyway but I would have lost too much speed, if that makes sense.

The higher you can keep those rpms climbing the steep grades the better off you are. Doing it manually or letting the tranny/computer do it doesn't really matter. In our twin diesel boat we generally ran the rpms at 90-92% of max.

[tom chelbana]

The reason we were on 154 was the 101 south was closed for 6 hrs. The 15 Essex wasn't in 6th gear pulling the grades but was in 5th and 4th at 1500 RPM. There are few times you should manually down gear when your speed is dropping and grade is long. Diesels are meant for working and sometimes you need to keep the RPM up.

[PanJH]

You need to watch the water and tranny temps-- lugging at too low RPM will raise them and could be the start of trouble. Knock it down an gear or 2 and get it in the sweet spot.

[lakebuster]

We have the 600 HP in a 17 LA. In the hills take the tranny out of economy mode and use the minus button if needed. Going up/down I-40 we used medium on brakes and it pulled like a beast in 4th gear. Remember 5th and 6th are OD according to specs.