[Vwdiesel] Brakes --- engine brakes -- ( The physics of it ).

[H.Hagar]

I love Physics --- it is good exercise for an old brain.

A lot of VW drivers say that the diesel does not slow down the
car going down a hill as well as a gasser.

Physics tells us that is MOSTLY   myth.    Do a test as follows and
you will be convinced.Use a "calibrated hill"  (Val). Start test at top of hill
with the fuel off. ---Check max speed going down.
Then do it again with fuel on .    If braking is a lot less  with fuel on, reset idle and
fueling screws a tad towards less idle rpm and less fuel.

The Bosch pumps are real tricky in that Idle range . Totally different from a carb.

What slows us down ????   ----heat loss --it takes a lot of heat going in to
the rad to slow things down.  ----That's where the diesel shines. Higher temp
in combustion chamber faster transfer of heat.

A fair amount of force is recovered with piston on downstroke. Air working
like a spring. More braking would result if valving was changed to Aircompressor
configuration.( I think that's the Jake --am I right?)

Let me say it again  ----if a fixed amount of fuel was injected , regardless of  rpm
there would be braking. The bosch pump is tricky , and may inject enough fuel to
ruin the slowdown.

The sum of all friction and powerloss according to Physics tells us that the  VW will
work as a brake going down that hill. How do I know ??? I live in hillbilly country.
Jackass Mountain  is a good proving ground. (that's close to Hells Gate).

The bosch pump is an amazing retarder ---- 4 flyweights thrashing around in fuel,  lots of
power loss. Turning at slightly faster than engine rpm.--so going down that hill with 5k
on the clock   the weights fly around at 5000 plus. That's what heats up the fuel in wintertime.
(and summertime).

Hagar.

PS: Here are a couple of physics teasers. ---- Water is a good Insulator both for heat and electricity.
Water is not heaviest when it is coldest.