Engine Brake - how do you evaluate it?

jvbronco · January 13, 2016

Driving home from work today and was thinking...

Is there any way to compare engine brake performance across the 3 truck brands?

Is it proportional to engine size?
How is engine brake performance measured? some sort of 'reverse' HP?
Is there a way to objectively compare the engine brake on the Duramax vs Powerstroke vs Cummins?
Any differences in how the brakes work across the 3 brands?

I'm the proud new owner of a 2016 Silverado 3500 HD with the Duramax. LOVE the truck. Had a 3/4 ton Ram with the 6.4l gas motor that developed a terrible engine tick and was literally creaking down the road on the interior at 5000 miles.

Figured I'd do it right and go back to GM (had good luck with my last two 1/2 ton Silverados) and just get a diesel.

Thanks!

MikeNH · January 13, 2016

Check out Fast Lane Truck on YouTube. They put all the trucks at max or near max payload/tow and go over the Eisenhower Pass in Colorado and among other things, measure brake temp at the end.

newdude · January 14, 2016

One thing to keep in mind on the light duty trucks. They use an exhaust brake and not an engine brake. The VGT vanes in the turbo create the exhaust backpressure for the system to slow the truck down.

Exhaust Brake Description and Operation
The exhaust brake system creates a restriction in the exhaust system that induces back pressure against the engine. This slows the vehicle using the engine and transmission. The exhaust brake system consists of the following components:

Body Control Module (BCM)

Engine Control Module (ECM)

Exhaust brake switch

Transmission Control Module (TCM)

Turbocharger assembly

Under certain conditions, the ECM will automatically close the turbocharger vanes to build back pressure in the exhaust. This increase in back pressure causes the engine speed to be reduced. The following conditions are required for the exhaust brake to be enabled :

Exhaust brake switch is On.

Antilock brake system (ABS) is not ACTIVE.

Automatic transmission fluid temperature is greater than 5°C (41°F).

Coolant temperature is greater than 30°C (86°F)

Transmission torque convertor is LOCKED.

Fuel system is in deceleration mode.

Vehicle speed is greater than 20 km/h (12 mph).

No Accelerator Pedal Position (APP) or Vehicle Speed Sensor (VSS) DTCs are active.

The ECM may also enable engine braking while the cruise control is active, to maintain the set target speed. This is called cruise grade braking. If cruise control is active and the exhaust brake switch is On, then the exhaust brake will activate when the vehicle speed is greater than 3 km/h (1.9 mph) over the set speed. The TCM makes this request along with a modified shift schedule, (more downshift availability), to hold the cruise set point on downhill grades.

To my knowledge, all of the big 3 use the same setup (VGT vanes close and create the backpressure). From what I've read on the Fords, you have to be in tow/haul for it to work, where GM's system is operational with or without tow/haul on. It is more effective with it on however, but you will still get exhaust braking with it off if you command the switch on.

A couple of the truck mags a few years back tested the three of them. GM had the strongest and most fluid functioning system, and Ram was right behind them.

jvbronco · January 16, 2016

One thing to keep in mind on the light duty trucks. They use an exhaust brake and not an engine brake. The VGT vanes in the turbo create the exhaust backpressure for the system to slow the truck down.

To my knowledge, all of the big 3 use the same setup (VGT vanes close and create the backpressure). From what I've read on the Fords, you have to be in tow/haul for it to work, where GM's system is operational with or without tow/haul on. It is more effective with it on however, but you will still get exhaust braking with it off if you command the switch on.

A couple of the truck mags a few years back tested the three of them. GM had the strongest and most fluid functioning system, and Ram was right behind them.

Good post - thanks for the info!

Cowpie · January 16, 2016

Not sure if the Allison also has a lot to do with it. On heavy trucks, the Allison in them also provides additional braking in conjunction with any engine braking. When you can head down a 3 mile 5-6% grade and never touch the brakes all the way down with a gross load of 78,000 lb, it is a good thing. True, the engine braking is different on a heavy truck, but any engine braking combined with transmission induced braking will be the cat's meow. Just not sure if the Allison in the pickups provide that level of performance.

newdude · January 16, 2016

Not sure if the Allison also has a lot to do with it. On heavy trucks, the Allison in them also provides additional braking in conjunction with any engine braking. When you can head down a 3 mile 5-6% grade and never touch the brakes all the way down with a gross load of 78,000 lb, it is a good thing. True, the engine braking is different on a heavy truck, but any engine braking combined with transmission induced braking will be the cat's meow. Just not sure if the Allison in the pickups provide that level of performance.

I Think that's where tow/haul comes into play with the exhaust brake. When you activate tow/haul you get the different shift points and line pressures, and then you get the tow/haul grade braking and more prominent downshifts, add the exhaust brake into the mix and it becomes quite the package.

jvbronco · January 16, 2016

On the interwebs, I've heard claims about Chevy's exhaust brake being "best in class". I'm looking for a way to objectively evaluate that statement and see which of the 3 is actually the best in class.

HP and torque numbers allow us to say which diesel engine has the best specifications. I'd like to find the same about the exhaust brake.

I'd like to note that this is purely out of curiosity - It's a great feature on these trucks. It would be nice to be able to know how they compare to each other.