do gassers offer anything like the DP engine brake

MrWizard wrote:
the new Allison trans with braking..for gassers is truly a wonderful piece of engineering

but..some facts about diesels and gassers are getting misconstrued
diesels have such good compression braking because.they are HIGH compression engines..like 20:1 much higher than gas engines
shut the fuel to a minimum and restrict the exhaust and it take a lot of energy to force that engine to rotate

diesel engines are "free breathers" ..the fuel is controlled NOT the air intake

gas engines both fuel and air are controlled..
BUT the air intake is restricted only when there is no throttle.. the gas engine does NOT have naturally occurring engine braking as some have suggested
restricting air intake..throttle body or carb flaps only reduces air into the take..(like suction).. it does not do anything to increase compression and reduce engine speed other than reducing combustion of fuel in the engine

diesel or gas ..tis all about low gears and good driving and Knowing how to use whats available

In truth. Diesels only have high compression on the front side. They have o on the back side. With out a exhaust brake. A diesel just free wheels.

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 ?

There is no redline for these motors. The computer will not let you hurt that motor. I've seen 5000 plus RPM on our rig when going down a very steep grade but the V10 was holding speed just fine. I use a combination of Cruise Control and Tow/Haul.

Welll, guys, all I know is what I have observed.
Gas engines have compression braking, even those old 7:1 compression ratio Model A 4 bangers. It is just the nature of the beast.
Diesel engines (at least the Cummins in my old Dodge 3500 and the little 4 banger in my older Datsun pickup) have negligible compression braking. The Dodge/Cummins however, had a Jacobs Rambrake installed on the engine, and when it was engaged there was a LOT of braking power! Since there was NO intake vacuum, it had a vacuum pump installed to supply vacuum to the cruise control, the Jake Brake, and the power brakes.
As for the throttle plate discussion, I have tried starting gas engines of various sizes by pushing or rolling down hills, and even with the throttle open there is a LOT of compression braking until the engine starts running (if it starts!).
My old Datsun diesel pickup had a throttle plate and venturi (the venturi created vacuum to control the injection pump via a diaphragm). With the throttle plate closed, it still had negligible compression braking.
I have no idea what the technical explanation of all this is, and don't really care. The observations are factual.

Oh, yeah, to answer the original quesation: No, there is no Jake brake or similar unit for gas engines. They don't need them. the inherent compression braking does the job just fine.

Mr. Wizard, you got things a little backwards....

Gas engine DO have natural engine braking, closing the throttle restricts the airflow through the engine, causing it to resist turning (engine braking)

Diesels have no natural engine braking at all (because there is no throttle plate to restrict airflow)take your foot off the gas (cuts fuel only) and it just freewheels.

Diesels get an addon engine brake (usually a pacbrake, which is a valve that closes off the exhaust, or these days with variable vane turbos, the brake is built into the turbo) to provide the engine braking that gassers get naturally (and a lot more of it usually)

In all cases, managing the transmission (manually is fine, or automatically with a tow/haul. Diesels have transmission management built into the pacbrake system)helps keep the speeds down.

Canadian Rainbirds wrote:


A lot depends on wheel/brake size. I learned to drive in British Columbia and am quite comfortable with mountain driving.

Years ago we drove our 30' 1997 Triple E Commander, on a Ford 460 chassis down the Espinazo del Diablo (Devil's Backbone) in Mexico, from Durango to Mazatlan. From 6,000 feet up to 9,000 ft, down to 6000 then back to 9000 then to sea level.

At one of the very few places to pull off I stopped for a "rest" break. Bad mistake. With no air moving past the wheels the drums on the 16" rear wheels heated the brake fluid to the point that there was vapour instead of fluid in the brake system. I pulled out behind a bus and braked for the corner and the pedal went to the floor :E Fortunately I was still going slow enough that I could pull it into 1st gear. A lot of pumping on the brake pedal gave me a little (just enough) braking. After following the bus downhill and pumping like mad when needed I regained reasonable braking in about 20 minutes.

We now drive a small (32') diesel pusher with 22.5" wheels, airbrakes and a great Allison 6 speed an excellent cruise control and exhaust brake.

Since you didn't say when you had last had your brake fluid flushed, it seems like you rode the brake pedal too much. Just 5% moisture in your brake fluid system will lower the boiling point of your brake fluid to under 300 degrees.
If your brake fluid had been flushed every two years, as recommended but very seldom done by RV owners, then you never would have boiled the fluid as you rode the brakes down the hill.
The fact that you could pump the brake pedal to get a little brake pressure indicates that you had moisture/steam in the brake lines.
Proper brake maintenance and not riding the brakes on a descent is very important for any RV that travels in the mountains.
I am sure that the brakes and wheel size on each RV is designed by engineers to handle the gross vehicle weight of your coach, if maintained and used properly.

the new Allison trans with braking..for gassers is truly a wonderful piece of engineering

but..some facts about diesels and gassers are getting misconstrued
diesels have such good compression braking because.they are HIGH compression engines..like 20:1 much higher than gas engines
shut the fuel to a minimum and restrict the exhaust and it take a lot of energy to force that engine to rotate

diesel engines are "free breathers" ..the fuel is controlled NOT the air intake

gas engines both fuel and air are controlled..
BUT the air intake is restricted only when there is no throttle.. the gas engine does NOT have naturally occurring engine braking as some have suggested
restricting air intake..throttle body or carb flaps only reduces air into the take..(like suction).. it does not do anything to increase compression and reduce engine speed other than reducing combustion of fuel in the engine

diesel or gas ..tis all about low gears and good driving and Knowing how to use whats available

rgatijnet1 wrote:
redguard just sent me this as a PM in reference to my post where I said that gasser RV's have no problems in the mountains with either the climb or the descent.

"you obviously have not driven a larger A gasser loaded in the rockies etc as this statement is pure bunk simply put UNTRUE "

I'll let those of you that have driven their gassers in the mountains respond. I have never had a problem with my Monaco gas coach in the Rockies, but I also never had a problem with the diesel coaches I've owned in the mountains.
Apparently he wanted to call me liar in private. Oh well! :B

As the above posts already seem to indicate, gas RV's do fine in the mountains.

A lot depends on wheel/brake size. I learned to drive in British Columbia and am quite comfortable with mountain driving.

Years ago we drove our 30' 1997 Triple E Commander, on a Ford 460 chassis down the Espinazo del Diablo (Devil's Backbone) in Mexico, from Durango to Mazatlan. From 6,000 feet up to 9,000 ft, down to 6000 then back to 9000 then to sea level.

At one of the very few places to pull off I stopped for a "rest" break. Bad mistake. With no air moving past the wheels the drums on the 16" rear wheels heated the brake fluid to the point that there was vapour instead of fluid in the brake system. I pulled out behind a bus and braked for the corner and the pedal went to the floor :E Fortunately I was still going slow enough that I could pull it into 1st gear. A lot of pumping on the brake pedal gave me a little (just enough) braking. After following the bus downhill and pumping like mad when needed I regained reasonable braking in about 20 minutes.

We now drive a small (32') diesel pusher with 22.5" wheels, airbrakes and a great Allison 6 speed an excellent cruise control and exhaust brake.

OOPS!

Thing is. Diesel Exhaust brakes were developed to give diesels the braking, that gas engines already had. You want to slow down a gas powered vehicle. Drop a gear, want to slow down more. Drop another one.

Gassers have a transmission brake as a lot posters mentioned! If your not aware DP's have a engine brake this is when a Jacob Head (hence the term Jake Brake) turns the engine into a compressor by closing all the valves in the engine, therefore creating back pressure! Good Question