Downshift or exhaust brake?

I never even thought about the higher compression ratio. You did all confirm my feeling that the EB is stronger. But with no real world experience I figured I'd ask.
Thanks everyone :)

4x4ord wrote:

Turtle n Peeps wrote:


The reason an exhaust brake works better on a diesel is because of the compression ratio. It takes a lot more energy to compress an 18 to 1 cylinder with air in it than a 10 to 1 cylinder with air in it.

The high compression ratio of a diesel contributes much to engine braking when a "Jake Brake" is used because the exhaust valve is opened at the top of the compression cycle. With these little pick ups and the exhaust brakes they have the compressed air is allowed to push the piston down on the powerstroke there by largely offsetting any braking that was accomplished on the compression stroke. The one thing that does make the diesel more effective at engine braking is the fact that the turbo is pushing more air through the engine than with a naturally aspirated engine. On the other hand the higher revving gasoline engine can pump more air than the diesel because it is comfortable revving higher.

The diesel with an exhaust brake is like an air compressor that leaks. It can build significant pressure against the piston when intake air is drawn in, compressed, re-expanded (cancelling the compression) then finally forced out through the restricted turbo in the exhaust. That final part is where it creates many psi against the top of the piston. Constrast that with a throttled gas engine where the most psi it can have acting against the piston is a pure vacuum at 14.7psi. Put an exhaust restriction on the gas engine and it too can have similar braking performance, although you’d actually want to open the throttle to force more air into that restriction.

Btw exhaust brakes, jake brakes, retarders, all different.

Didn’t read 4 pages.
Answer to original question. Yes.

Btw, the light duty trucks have an exhaust brake, not an engine brake. Two totally different things.

rhagfo wrote:
Well are you referencing an exhaust brake or engine brake?.

Neither ,, What is on my 8.3 is a simple throttle valve, that closes when the switch is in the on position.

Turtle n Peeps wrote:


The reason an exhaust brake works better on a diesel is because of the compression ratio. It takes a lot more energy to compress an 18 to 1 cylinder with air in it than a 10 to 1 cylinder with air in it.

The high compression ratio of a diesel contributes much to engine braking when a "Jake Brake" is used because the exhaust valve is opened at the top of the compression cycle. With these little pick ups and the exhaust brakes they have the compressed air is allowed to push the piston down on the powerstroke there by largely offsetting any braking that was accomplished on the compression stroke. The one thing that does make the diesel more effective at engine braking is the fact that the turbo is pushing more air through the engine than with a naturally aspirated engine. On the other hand the higher revving gasoline engine can pump more air than the diesel because it is comfortable revving higher.

Tom/Barb wrote:

rjstractor wrote:

However, as has been stated, a modern diesel (or even one like mine with an add-on) with an exhaust brake will provide significantly better engine braking than a gas engine, mostly by virtue of a much higher compression ratio.

That's not true with a Cummins. They really don't have an exhaust brake Like a Caterpillar.

Well are you referencing an exhaust brake or engine brake?
Newer exhaust brakes are handled with variable turbos, not a true butterfly valve like a PacBrake. Engine brakes typically alter the valve train operation.

rjstractor wrote:

However, as has been stated, a modern diesel (or even one like mine with an add-on) with an exhaust brake will provide significantly better engine braking than a gas engine, mostly by virtue of a much higher compression ratio.

That's not true with a Cummins. They really don't have an exhaust brake Like a Caterpillar.

On My Cummins 8.3 with a banks intake and exhaust kit, the intake is blocked, as in an intake choke. there is nothing on the exhaust side. (just like a gas engine)

When I click the engine brake on, fuel flow goes to 0, the transmittion shifts to 4th. On steep hills I'll drop it one more (3rd)

When I feed fuel the brake will go off and transmission will shift up. as soon as I take my foot off the throttle, the brake goes on and the transmission will shift back down.