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Old 11-23-2009, 03:27 PM   #1 (permalink)
Jager
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Engine Brake vs Exhaust Brake

I was talking to a friend about my new truck and he asked if it had an engine brake or an exhaust brake. I said it had an "engine exhaust brake" since that is what it is called on the spec sheet. He told me they are two different things.

I assume an engine brake is the same things as a jake brake - (from Wikipedia) Also known as Compression Braking, this is used mainly in large diesel trucks. It works by opening the exhaust valves at the top of the compression stroke, releasing the compressed air in a pop so it can't push the cylinder back out.

From Wikipedia exhaust brakes were explained as closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine.

I assume we have an exhaust brake and not a Jake brake. It sounds like the exhaust brake would be better anyway.

Does anyone know if there is also a EPM (exhaust pressure modulation) system used on our system?
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Old 11-23-2009, 04:19 PM   #2 (permalink)
Carl Lassiter
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A Jake brake is an "exhaust brake". It takes it name from the company- Jacobs- who makes most of the exhaust brakes on big rigs. Where it gets confusing is exhaust brakes/jake brakes are sometimes referred to as engine brakes and vice versa (through compression release), if memory serves me correctly. That is where the confusion with your spec sheet comes in.

Exhaust brakes are superior to engine brakes at helping stop BIG weight, which simply gear down to slow. All big rigs have exhaust brakes, they are noisier and rougher than engine braking hence why they are not usually available on light trucks, though the Dodge Ram Cummins series does feature them as standard with the new 6.7.

I believe your truck is equipped with the Allison 1000, if so you have "engine braking"
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Old 11-23-2009, 06:15 PM   #3 (permalink)
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My 2003 C4500 came stock with a exhaust brake. It works great when towing!!
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Old 11-24-2009, 04:45 AM   #4 (permalink)
ronjhall
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Your engine came with a Exhaust Brake. The 2006 and on GM MD Duramax trucks uses the Variable Vanes of the Turbo to create the back pressure needed to work as a exhaust brake.
Older versions of the MD truck used a exhaust brake in the exhaust pipe.
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Old 11-24-2009, 08:14 AM   #5 (permalink)
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Quote:
Originally Posted by Carl Lassiter View Post
. . .
I believe your truck is equipped with the Allison 1000, if so you have "engine braking"
Hey Carl, Thanks for the extra information . . . very helpful. When I was reading about them it seemed like the exhaust brake would be better than an engine brake.

My truck, 2008 Kodiak 4500 has the MHE - Allison 2350 6sp tranny and K40 engine exhaust brake. However I have a friend who has a 2005 Kodiak 4500 with an Allison 1000 and he also has an exhaust brake.

It would seem like using an exhaust brake would put a lot of extra stress and strain on the engine and exhaust ports. I guess they must be designed to handle this.

For those of you that tow heavy loads do you find yourself using the exhaust brake all the time or just in emergencies?
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Old 11-24-2009, 11:18 AM   #6 (permalink)
ronjhall
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A Allison 1000 can have an exhaust brake. Mine does.
Big rigs have engine brakes.
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Old 11-24-2009, 01:14 PM   #7 (permalink)
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I use mine going down steep grades and short offramps. It saves the brakes so they are ready for emergencies. When I lift off the go pedel the trans downshifts and the exhaust valve closes. Works great!!!
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Old 11-24-2009, 01:21 PM   #8 (permalink)
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Quote:
Originally Posted by ronjhall View Post
A Allison 1000 can have an exhaust brake. Mine does.
Big rigs have engine brakes.
I wasn't sure about the Allison 1000 and didn't word it very well to reflect that, good to hear.

However, it's my understanding that big rigs generally have Jake Brakes, which are exhaust brakes even though they can be referred to as engine brakes. If I'm wrong on this then my apologies to Jager.
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Old 11-24-2009, 01:38 PM   #9 (permalink)
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Quote:
Originally Posted by Carl Lassiter View Post
I wasn't sure about the Allison 1000 and didn't word it very well to reflect that, good to hear.

However, it's my understanding that big rigs generally have Jake Brakes, which are exhaust brakes even though they can be referred to as engine brakes. If I'm wrong on this then my apologies to Jager.
Simple explanation of a Jake Brake (engine brake) is the engine is turned into a air compressor. Using the drive train to power it as truck slows.
A Exhaust Brake blocks the exhaust from exiting out of engine. This cause back pressure and slows the truck down.
Both systems use the transmission and drive train in a lower gear to increase rpm,s. More rpm's, more stopping power.
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Old 11-24-2009, 04:24 PM   #10 (permalink)
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Some people here are confusing these brakes.
Even though the Allison programming includes "Engine braking" all it really does is backshift the tranny sooner and provide compression braking through engine speed.

Jacobs brakes, or "Jake Brakes" include a modified cylinder head and controller. When activated, effectively turns the engine into an air compressor. These are the real engine brakes.

Exhaust brakes are inline the exhaust system (See PacBrake) and use a butterfly valve to restrict the exhaust flow, causing back pressure and negative work.

VVT Brakes simply use the VVT turbo vanes to restrict exhaust in the turbo rather than inline with the exhaust. All accomplish the same thing in the end, but several ways of doing it. As of now, Jake brakes aren't offered for our trucks, and probably won't be. You can get an exhaust brake, or tuning via Banks or EFI Live to control the VVT if you've got an 04.5 or newer. Hope this helps
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