6" SS EXHAUST STACK

[Pete Masterson]

Tom,

I appreciate your explanation ... but it is a reality that the
"engine braking" performance seems to be less effective after the new
muffler than before. Perhaps this is a matter of perception (as it is
_not_ as loud) but I suspect that the increased back-pressure in the
exhaust system is making the engine braking slightly less effective.

Here is an explanation of what a "Jake Brake" engine compression
braking system is:

A compression release engine brake uses an extra lobe on the camshaft
to open a second exhaust valve at the top of the compression stroke.
The stem of this valve telescopes during normal operation so the
valve remains closed, but is locked at full length by a solenoid when
the engine brake is engaged so that the valve opens as directed by
the cam. This releases the compressed air in the cylinder preventing
it from returning its energy back to the piston and accordingly, the
vehicle speed is reduced.

The driver controls consist of an on/off switch and, sometimes, a
multi-position switch that controls the number of cylinders on which
the brake is active. When the compression release engine brake is
turned on, it will activate when the driver releases the accelerator.
There are also switches on the clutch and accelerator pedals that
will deactivate the compression brake when the clutch is disengaged
or the accelerator is pressed.

Without doing a LOT more research in my DD documentation than I care
to do at the moment, I can't say for certain exactly how the DD
Series 60 engine braking system is designed, or if it is a true
engine compression system braking system as described above.
(However, the control system described seems to reflect the
operational characteristics of the system on my coach.)

As installed on the BB, it is pretty obvious (due to the noise level
reduction after installation) that the engine braking exhaust is
dumped through the exhaust system. Originally, many over-the-road
trucks dumped the compression braking exhaust directly without
passing through the exhaust system (since there are no noxious fumes
or much heat (compared to the burnt fuel under power) are present,
the routing issue isn't as important). This caused the very loud
"blat-blat-blat" sound (once) commonly heard from large trucks as
they decelerated -- resulting in restrictive local ordinances
restricting use and in many states, requirements that "engine
braking" systems pass through a muffler.

In my research, I note that DD Series 60 engines built after 2000
"have a new-design engine braking system." I also note that there was
a recall on the '95 (and possibly later year BBs) where the 2-4-6
cylinder system was rewired to only have "low" and "high", due to a
flaw in the DDEC and/or other control systems. (I presume the low and
high are 2 cyl or 6 cyl engine compression braking.) You can see if
the "fix" was applied to your coach by examining the solenoids on the
upper-right (as you face it) of the front power center where you will
see one of the three associated with the engine braking system "wired
out."

Pete Masterson
'95 Blue Bird Wanderlodge WBDA 42
aeonix1@...
On the road at



On Nov 6, 2008, at 12:14 AM, Tom McCarthy wrote:

> Pete, I do not think our Jacobs brake is exhaust based at all. It is
> an engine brake that uses the compression of the DD60 to "brake." It
> shut down fuel to certain cylinders at the upstroke that normally is
> pushed by combustion. This is as far out on the limb with mechanics
> that I am willing to go. This is based on an FMCA DD seminar on DD
> 60 Jacobs braking.
>
> TTS McCarthy
> Poway, CA
>
> --- In WanderlodgeForum@yahoogroups.com, Pete Masterson
> wrote:
>>
>> Having recently replaced my muffler (at great expense) -- had I to
> do
>> it over again, I'd have switched over to a 5" system from turbo to
>> stack. As others have stated, it's 5" at the turbo outlet and the
>> standard in the heavy truck industry is 5".
>>
>> The only performance difference I notice (between the old blown
> out
>> muffler and the new one) is that the exhaust-type Jake brake seems
> to
>> be slightly less effective.
>>
>> Pete Masterson
>> '95 Blue Bird Wanderlodge WBDA 42
>> aeonix1@...
>> On the road at Hohenwald, TN (Natchez Trace Parkway)
>>
>>
>>