Engine braking Gas Vs Diesel

I still don't buy into this whole idea that gas engines are so much better at engine braking.

On the farm, I spent many years hauling loaded wagons from the field to the barn that weighed upwards of 10 tons. It was generally downhill back to the barn so much of the trip involved "engine braking."

For many years in the '80s and early '90s, I hauled with a gasoline powered tractor, and "engine braking" was only good for a couple of seconds at the top of the hill. From there on you rode the brakes the rest of the way down the hill to keep the engine from overspeeding.

In the mid '90s we got a diesel tractor about the same HP and weight as the gas tractor we had been using. That diesel tractor handles the load SO MUCH BETTER. It holds the same loads almost all the way down the same hills at the same speeds with almost no braking needed.

Same thing can be shown with an empty tractor. Going down the road, you pull back the throttle of the gasoline tractor, and it just coasts, driving the engine. Without brakes, you'd sail right on by the driveway. Pull back the throttle on the diesel, and it's like you threw out the anchor.

RCMAN46 wrote:
I do not believe the diesels used in the pickups have true Jake brakes.

The braking is done with the turbo and not with valve timing as in the big rigs.

Ram calls it a Jake brake but it really is not a true Jake brake.

If you go to the Jacobs website you will see that they say that ANY engine braking system that is manufactured by Jacobs IS a "Jake Brake".
If the manufacturer says the Jacobs Rambrake used on Dodge/Ram pickups is a Jake Brake, that is good enough for me!

brulaz wrote:

It also makes sense that the RAM Ecodiesel has weak engine braking, from what I've read in the forums probably worse than my 3.5L EcoB, because it does not implement an exhaust brake.

The EcoD does not come with any exhaust brake from the factory. It does have some transmission braking. If you get the Green Diesel Tune, they have an option of Exhaust braking about 2700 RPMs, Transmission in 6th of less (Doesn't work in 7th or 8th).

Me Again wrote:
I wonder how the new direct injection gas engines are doing that have no butterfly valve? Audi, BMW and Mini Cooper all have engines in production with DI.

I was under the impression that DI just places the fuel injector in the combustion chamber instead of the intake runner. They should still have a throttle body to let air into the engine. I could be wrong.

Thing is. Diesels need add ons to have the same braking as gas engines do naturally. Mostly because of back pressure. Diesels have tons of compression on the front side. But have a HUGE hole on the back side. Result, no back pressure, and no engine braking. Which is exactly why Jake brakes were invented. To give diesels engine braking.

IMOP. No diesels should be sold with out some kind of add on braking system. Be it exhaust, or, trany brakes.

rhagfo wrote:

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BRULAZ wrote:
My 2011 F150 with the 3.5L EcoB has good engine/tranny braking in Tow/Haul mode, but on some steep and windy Appalachian trails I've needed to let it wind up to 4000-5000 rpm in first gear so as not to cook the truck+trailer brakes. From what I'm reading here, a similarly sized diesel without an exhaust brake would be worse.

Wow, and how fast were you still moving, lowest gear I have ever needed was 3rd, on my 5 speed, traffic was down to about 40.

Down west slope of Newfound Gap in Smoky Mountains National Park. Speed limit was 35mph, many hairpin turns with 20mph speed limit.
The Dragon's Tail just south of the park is similar but not as steep.
Not talking Interstate Highway travel here!
Think I was up to 30mph at 5000 rpm in first gear.

RCMAN46 wrote:
I do not believe the diesels used in the pickups have true Jake brakes.

The braking is done with the turbo and not with valve timing as in the big rigs.

Ram calls it a Jake brake but it really is not a true Jake brake.

Well the Cummins 6.7 can be equipped with a true engine brake, PacBrake has a kit. That is not badly priced.
Pacbrake Loadleash Engine Brake


My 01 with a after market PacBrake will slow well enough in Direct drive 4th on a 5 speed that I need to either release it or apply a little throttle.

BRULAZ wrote:
My 2011 F150 with the 3.5L EcoB has good engine/tranny braking in Tow/Haul mode, but on some steep and windy Appalachian trails I've needed to let it wind up to 4000-5000 rpm in first gear so as not to cook the truck+trailer brakes. From what I'm reading here, a similarly sized diesel without an exhaust brake would be worse.

Wow, and how fast were you still moving, lowest gear I have ever needed was 3rd, on my 5 speed, traffic was down to about 40.

Me Again wrote:
I wonder how the new direct injection gas engines are doing that have no butterfly valve? Audi, BMW and Mini Cooper all have engines in production with DI.
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Good point. The F150's 3.5L Ecoboost is Direct Injection, so possibly no air throttle plate, but it does have twin turbos. Maybe not that different from a similar turbo diesel with no exhaust brake after all.

Can a gas DI engine with turbos and no throttle plate ever have an exhaust brake?

I do not believe the diesels used in the pickups have true Jake brakes.

The braking is done with the turbo and not with valve timing as in the big rigs.

Ram calls it a Jake brake but it really is not a true Jake brake.

I wonder how the new direct injection gas engines are doing that have no butterfly valve? Audi, BMW and Mini Cooper all have engines in production with DI.

Back to grade braking! For some reason the V8 diesels in GM and Ford trucks held back better than the Cummins I6 did in the RAMs. Maybe it was the much heavier rotating mass of the Cummins. I know from experience with my 2001.5 RAM that when I had just the smart controller on to keep the torque converter locked with the exhaust brake off, that the engine just free wheeled down grades without hardly any hold back. Chris