do gassers offer anything like the DP engine brake

I have gone down some 10% grades in my older 97 Ford Bounder class A, 30' long and 16,500 pounds with a 17,000 GVWR! It has the same brakes as the then current F-450 and F-550 trucks. THey are HUGE disk brake rotors and pads about 6" tall and 2" wide! They are much larger than any car that I have ever changed.

Anyway going down the 10% grade, I would slow to less than 40 MPH and shift to second gear, and that brings up RPM to about 3,000. At 3,000 RPM, the engine braking is significant, and would help slow the motorhome a lot. Letting it rise to 3,600 would provide even more braking. That is about the limit that I would put to my transmission. The 2005 and later Ford transmissions can handle the engine turning 4,200 RPM downhill, and provide much more engine braking than my engine, plus most newer cars shut off fuel to the fuel injectors to provide more braking and help slow the vehicle, and save fuel too!

My motorhome will beat my buddy's Country Coach with a 10 liter diesel engine up a long grade, such as the climb to Mammoth Mountain! That is because it is lighter weight, and can run higher RPM than a diesel can. The V10 can run 4,400 RPM intermittently, and 4,200 RPM all day long. This is because of the tiny 0.68 liters per cylinder. Think of my 460 V8 (7.5L) as nearly 1 liter per cylinder (about the diameter of a 2 liter soda bottle, but 1/2 as tall). The 8.3L inline 6 Cummings DP would have about 6" diameter and 6" stroke, with 1.4 liters per cylinder. The Cummings 8.3L max RPM is only about 2,500 - 2,700 depending on the model and year. It is that huge stroke length that prevents them from going to such a high RPM, and prevents the DP from getting to much engine braking unless they also shut off the exhaust gas flow.

So don't be bothered by not having the engine brake. Gas engines can have just as much braking power as a DP, in perportion to their weight.

Also when going down a hill, DP or gas engine, make sure to get out of overdrive, and downshift one more gear if required. Turning on the engine brake on my buddy's Country Coach would shift it from 6 to 4th gear, and close off the exhaust airflow by about 85% to 90% covered.

In my gas motorhome, I would shift out of OD, then shift to 2nd gear if required (after slowing below 45 MPH in my case (with a 4 speed auto). This normally provides enough engine braking that I never need to touch the service brakes going down a hill on a interstate freeway (where downgrades are 6% or less steep). It is only a really steep 2 lane road, or perhaps coming up on a 35 MPH curve that I would use the service brakes in my motorhome.

Good luck!

Fred.

You have to use a combination of engine braking and at times when it starts to rev up too much apply some brakes to bring the rpm's down.

kgard1225 wrote:
Thanks for all the replies. I wasn't sure if the engine rpms would get too high going down a steep descent keeping in a low gear. All of the late model gassers I have been looking at had Ford chassis with the V-10. What is redline on these motors ?

That is a good question. I don't know the answer but I've always wondered if the gas engine is effectively braking during a downhill run of say 10 percent what happens with the engine/rpms/transmission if the grade were to drop to say 20%…? Would the engine rpm continue to climb? Does the transmission further compensate in some manner? If you don't touch the brakes what blows up first; engine or transmission?

RayChez wrote:
Yes gasoline motorhomes with big engines have lots of power, but man they eat gasoline like crazy. I had a 454 chevy pickup with a big overhead camper. I started climbing the Sierra's from Bishop to Mammoth. It went up easy, but I was almost out of fuel by the time I got to the top of the mountain. LOL! And the Ford 460 was even worse.

Many years ago, when I lived in the Flathead Valley of Northwestern Montana, not far from the West entrance to Glacier National Park, I had a 1969 Chevy C20 that was like that. I had a 9 foot camper on it, and it had the old 292 inline 6 with 4 speed tranny.
That thing had a terrible thirst for fuel!
I haven't done a fuel economy check on the Southwind (I don't really care), but from here to Great Falls it seems to take pretty much the same amount of fuel as the old Tioga 29 Foot Class C with the 460 Ford did.

Thanks for all the replies. I wasn't sure if the engine rpms would get too high going down a steep descent keeping in a low gear. All of the late model gassers I have been looking at had Ford chassis with the V-10. What is redline on these motors ?

Of course if we are going to try to confuse the issue with a money diet for fuel I would suggest a smart car and a tent. When I can't afford fuel I will sell my MH.

If you know how to drive, either with or without an exhaust brake, using your gears it will slow you down to a crawl if you wanted to without using your brakes. Even with an exhaust brake on a diesel you have to tap the air brakes every once in a while if it starts picking up speed, and they will on long steep grades.

Paul,

I look at it a little differently.

The correct speed of descent in any heavy vehicle is the speed/gear/use of any non-service brake that keeps your speed in EQUILIBRIUM. That is you are neither speeding up nor slowing down and do not need to use your service brakes to do this.

We were descending a 17% grade in the Green Mountains of VT several years ago. 2nd gear with exhaust brake on-- doing about 22 MPH. We easily could have taken the curves at 35-40 MPH (so grade, not road shape dictated speed). Dianne was worried that someone would run up on us. Around the next bend was a loaded logging truck, doing his equilibrium speed-- about 8 MPH. We blasted right by him and continued on down the mountain. Both of us were descending correctly for our rigs.

I'll just pile on a bit here. We have driven over the Rockies, through the Canadian Rockies and down into Presidio TX in both a gasser (8.1L GM with Allison) and in our current DP with Engine Brake. No problem in either coach towing our car behind (RAV 4 behind the gasser and Jeep Wrangler behind the DP. The secret is to drive down the grade at the speed you came up, in the gear you came up. So if I crest at 30 mph in 2nd, that is how I start down and I use engine braking or EBrake to hold the speed. If the speed rises I apply the brakes firmly just long enough to get to 5 mph below my desired speed. Never let it get away from you, it will be a wild ride no matter what system you have, not that I have any experience of that.

We are combining several very different issues:

The mechanical aspects (basically braking HP/weight)-- a matter of physics!

The "driver" aspects. Some can safely drive ANYTHING anywhere. Others with no mountain experience are very different and need a machine that will "forgive" their mistakes. Add to that that there are a lot of drivers with no mechanical background-- who don't even know that you can't use your service brakes to keep speed down on a long descent in ANY heavy vehicle. Who don't know that brake fluid's boiling point drops with age, etc. IMO the driver is the more critical part of the equation.

Bottom line is there is more to the equation than machine alone.