[Vwdiesel] Diesel braking - again

[James Hansen]

> change the valve timing.  I would assume Jacobs Engineering works very
closely with the major diesel engine mfgs. to make sure the engine design
can accomodate the Jake brake components.  And I assume a setup like that
adds a lot of $$$ to the cost of the
> engine.

Yes, and yes.  The black art of exhaust valve retarding, but since they are
essentially just introducing lots of lash into the system. It's just a bolt
on item for most highway engines.  Uses oil pressure to activate.

> double the engine power and you are severely underpowered (both
accelerating and braking) compared to a light vehicle.  So instead of
overdesigning the engine for the big rig, you just beef up the engine
braking capabilities and rely on gearing in the
> transmission to handle the braking needs.

Friend's truck has 600 hp going through a 10 speed, and can select 2, 4, or
500hp braking force via the retarder, uses a Jacobs I think. Mack used to
have their own, called dynatard.  Nothing shy about braking either- you can
lock the wheels up on a fully loaded truck with king bee trailers on them-
that is load of almost 50 metric tonnes in two trailers plus the truck,
riding on 9 axles with a total of 34 wheels. Using the brakes is expensive,
the engine brake runs pretty cheap.

>
> I would imagine if you could rig up a Jake brake on a small VW diesel
engine in a light, unibody Rabbit, it might lock up the wheels if you hit it
at high RPM.  You would have so much braking force that you would not be
able to use it on all but the
> steepest of grades.

Big if.  Overhead cam engines would be tough to accomplish this in.
Imagine the possibilities in another few years when we get diesels with
solenoid controlled valves. woo hoo!


 Full size pickups used for towing can benefit from an exhaust restriction
type of brake, not as effective as a Jake brake, but probably good enough
and assuming the engine design can handle the increased back pressure
(stiffer valve
> springs), installing a system is pretty much a bolt-on install, assuming
the availability of a kit.

Basically a servo motor controlled ball valve.
I'm not a fan of this system, reminds me too much of kids stuffing a potatoe
in the exhaust pipe.
-James