Wow, 5 to 18psi of retarding pressure provided by the "exhaust brake. " Dodge's with either a Cummins-Jacobs, PacBrake, or other aftermarket brake have always provided up to 60 psi of braking.
I guess if a buyer doesn't know the difference between turbo boost and exhaust back pressure it helps explain why he would buy a GM truck with a car type Japanese V8 diesel, even though Isuzu builds hundreds of thousands of inline four or inline six cylinder real diesel engines.
This buyer certainly knows the difference between turbo boost and exhaust back pressure.
Actually Harvey, I didn't say 5 to 18 psi of
retarding pressure. Let me explain how the brake in the GM works a little bit better since you don't seem to understand how the braking system works with a VGT turbo.
There is no secondary module with a flapper valve like in your truck, all the braking is done using strictly the turbo and the engine computer. The computer closes the drive vanes (exhaust side) on the turbo, creating back pressure. This in turn spools up the turbo and the driven (intake side) is obviously spooled up as well. That is what creates the 5-18 psi of pressure I was talking about. Positive manifold boost pressure from the turbo, 18lbs of boost, just as if you were on the throttle. In turn, this additional manifold pressure creates more exhaust going thru the vanes of the drive side of the turbo, thus creating even more manifold pressure on the driven side. Basically the more the brake works, the more it can work if you will. It's a pretty ingenious system, working much better than the "on off" flapper valve style you are used to. Since it is computer controlled it is completely variable based on the load and grade you are descending.
Previous models of GM vehicles using the after market flapper valve style were limited from 55 to 60psi of exhaust back pressure from what I could find looking at a few manufacturers web sites. Appears to be the same amount Dodge uses. However GM didn't require replacement of the valve springs the way Dodge did in the earlier years.
Edit:
To add another feature of the GM brake since a member posted about not being too fond of how the transmission downshifts in the Dodge no matter what:
While using Cruise Control the GM brake will turn on
before the transmission downshifts, then it will downshift the transmission as necessary based on the load. Opposite of how the Dodge downshifts then turns the brake on. Also, if you want to prevent the truck from downshifting at all and just stay in whatever gear you choose, simply put the transmission in manual mode and select your gear. The transmission will hold that gear and the computer will ramp up the brake to maximum retarding pressure. However you will gain speed as expected if it is a steep hill. I love this feature since on some of the hills you can see you are about to the bottom and it's no big deal if the truck gains 5 - 10 mph.
The GM brake has a much softer engagement / disengagement as well. It doesn't jerk the truck the way the Dodge does when loaded heavy.
When you factor all that in on top of that it has more retarding ability than the Dodge, it really is a pretty slick system. Perhaps someone who is able to keep an open mind should go for a drive in a new GM truck, I really feel they would be impressed with how the transmission, cruise, and brake all work together seamlessly.
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