[A/S] Exhaust Brake Performance

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxxxxx>]

Tom,

You should see some additional braking provided by the exhaust brake in the
hills around Kerrville.  I don't know how much your device will produce.

Exhaust brakes will never actually stop the vehicle(s) but will only
increase braking effectiveness while reducing the load (and wear) on the
truck's service brakes.  Their effect is quite pronounced on a manual
transmission vehicle, I have no experience with using one on an automatic
transmission-equipped puller.

Jacobs, Pacbrake, BD, and others who manufacture exhaust brakes rate them in
terms of retarding horsepower.  As engine rpm increases, retarding
horsepower increases.  This occurs because greater engine speed equals
increased exhaust gas discharged.  When the exhaust exit is blocked by the
butterfly valve of the exhaust brake, more retarding force is created.
Downshifting to a lower gear increases engine speed which produces
additional engine exhaust braking for the same road speed.  My Jacobs brake
will hold back my truck and trailer with a GCW of 16k # on a 9% downgrade
without using the service brakes at all if I downshift from 6th gear
overdrive to 4th gear.

If you go to the Jacobs web site
http://www.jakebrake.com/popup-ex/three.html  for the Dodge Ram application,
you will see the graph showing retarding horsepower at given engine speed.
Jacobs claims that the jake brake installed in a Dodge Ram produces 143
retarding horsepower at 3100 rpm.   This should give you some idea how the
traditional exhaust brakes perform in order to evaluate yours.

The claims may vary between manufacturers but I would guess all traditional
exhaust brakes produce similar results when installed on the same engine
because the engine's volume of exhaust discharge and the size of the exhaust
pipe are the same.  The only difference between the products should be the
amount of leakage allowed past the butterfly valve.

I don't know how the Ford PSD fast warm-up device you are using compares.

My jakebrake has about a one and one half second delay after the throttle
closes also.  The computer establishes this delay so that on a manual
transmission-equipped truck you won't get jake brake application when
shifting gears in normal driving.  The throttle has to be closed for the
specified delay before brake application occurs.

Let us know how your brake works.

Harvey