[Vwdiesel] Diesel braking - again

[Erik Lane]

ok, i've been thinking about this. sorry to bring this
up again, but i just can't get it off my mind. :)


i've been driving diesels for many years and have
never noticed a problem using the engine for a brake.
of course, since i only use it when there's a REALLY
long hill or some such i might not use engine braking
as much as some of you. and i don't drive gassers as
much as i do diesels, but when i do i've never noticed
that much of a difference. i find it hard to believe
that would have missed it, but of course it's
possible. you can bet next chance i get i'm gonna be
testing it!

my understanding of the physics and all might be
mistaken, but seems to me the higher compression is
still a large factor, even when the air is let back
out on the exhaust stroke. the diesel starters are
much larger than the gas equivalent, and they spin the
motors slower, in my experience. even with a fresh
battery and not counting the first few turns, when
arguably the engine hadn't had a chance for the
compression vs exhaust to equalize, it still seems to
take a LOT more power to turn.

and if a gasser is pulling against a vaccuum that also
means that the air density in the cylinder when it
goes to compression is VASTLY reduced. that's a lot
less work.

yes, a diesel gives more fuel at higher rpms. but so
does any engine, what does that have to do with it? if
it's a gasser and port fuel injected then it will get
more squirts of fuel for every intake stroke. if it's
mass fuel injected then it will increase for the
increase of air crossing over the air metering device.
(cause even tho it's pulling against a vaccuum it
should still pull more air as the engine speeds up,
right?) and with a carb higher vaccuum will cause a
greater differential across the metering screw and let
more fuel in that way.

i'm not tryin to say that they are exactly the same.
just tryin to theorize why there wouldn't be that much
of difference, like it has been in MY experience.
maybe some people's injection pump settings are a bit
high at idle? but one of mine has always idled a bit
high and it still has good engine braking if needed.

i don't want to fight anyone or argue. i'm just trying
to understand and match what i see in the real world
with my undertanding of HOW it all works. so if
someone can see where what i'm saying is faulty,
please let me know. (just tryin to be extra careful,
cause i don't always come across well on the
computer.)

sorry again for dragging this out again.

regards,
erik

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