Congratulations G.M.C, again!

Yes ford does need a better exhaust brake system. But overall they do fairly well in downhill grades aside from this testing runs.

Exhaust brakes are like a reverse HP activity, and because the Duramax V8 can tolerate a lot more rpm than the Cummins I6, it can ultimately put down more retardation. I know guys who have spun the D-max up to 5400rpm downshifting the Allison. I wonder how the Cummins would have done with the 6speed manual. Then again, the TWR with the MT is WAY lower...

@Mrknowitall - valid point. I remember when exhaust brakes first came out "Jake brake" was the most common system I remember. There were guys that were blowing engines because of over revving.
The Cummins system does look like the best system but only if the tranny would of done its job.

It is interesting to note that these tests favor the Ford tranny over the Allison tranny.

Diesel engines have two redlines: one under combustion pressure, and another for overrun retardation.

Pickuptrucks.com should have found out what the limits are, and posted them. (Don't you guys have contacts at Ford/GM/Chrysler?)

Secondly, all of these engines have intake throttles-which control eEGR, why aren't they integrated into the whole engine brake package?
Are pickups that much less sophisticated than the rest of the automobile universe?

@George- under vacuume, tbe engine has less retardation than under pressure. That means the throttle is less effective than an exhaust brake.
@Lou- while the V8's can safely spin to over 5 grand, the I-6 just isn't built for that. Ultimately, that means less retardation, no matter what the transmission.

Everybody:: there are 4 types of braking systems, 1) is the brakes built into the wheels, 2) then there is the (exhaust) brake where the exhuast system is mechanicly blocked when you take you foot off the fuel pedal. 3) then there is the (Jake-brake), where inside the engine there are soliniods atached to some of the valves, this is where it can get compicated because there are diff. systems, the top of the line offers 3 of the 6 cly or 2 of the 6cly or1 of the cly to work for diff. levels of retardation, it is diff. on 12,8,6,4, cly engines all diff. types. and 4) Caterpilar has a very complicated sys. of oil passages in the fly-wheel, that creates resistance with a lever on the steering colume. The most common on p/u's thou are exhaust type brakes! and finaly some of these systems word with cruze control when you gain speed going down hill. Sandman 4X4

@Mr. Knowitall.
I didn't say that the intake throttles need to be fully closed, but closed so that there is negative work done on the intake stroked.(60 degrees or so)
This would help with the negative work done on the exhaust stroke from an exhaust restriction system.
Fully throttling would nullify the exhaust brake.

Yes, an exhaust brake has more possible negative power potential because you can only get 1 atmosphere of pressure differential from vacuum. But how much cool air (relative to the normal combustion exhaust gas temperature) can be pumped into the exhaust system before the catalytic converter cools below the critical temperature?

@George- I see what you're talking about. I'd have to check what we do here as far as using the throttle. For the catalytic cooling off, the energy that is being absorbed by the engine, is largely put into heating the expelled air (friction from being forced through the exhaust brake. This will keep the cats warm to some extent. worst case, it behaves like on cold start for a bit. Should warm right back up- what goes down, usually goes right back up.