[Vwdiesel] Diesel braking - again

[Erik Lane]

sorry, i guess i misunderstood and took what you were
saying a little too literally.

--- Roger Brown <r.c.brown at ieee.org> wrote:
<snip>
> I stand corrected, I should have used a different
> wording for that.  The higher compression in a
> diesel is going to make the compressed air hotter
> resulting in a more heat transferred to the coolant
> and thus a bit less energy returned to the piston. 
> However, since there is less volume of air entering
> the engine through the intake restriction, the
> internal pressure in the diesel (and the gas) engine
> is less, I commonly see 25" of Hg on my gas engine
> vacuum gauge near sea level while engine braking,
> that means that only 1/6 of the normal air volume is
> getting in (30" is nearly a perfect vacuum).  So,
> instead of having say 500 psi (or whatever the
> normal number is) in the diesel, you only have 500/6
> or 83 psi in the cylinders.  Your gas engine would
> be 25 psi (assuming 150 psi normally), so there will
> be a little difference due to the differences in
> pressure, but neither one will be anything near what
> it would be with no intake restriction.  So if you
> have a one factor (i.e. intake restriction) and
> another factor (braking due to pumping/heat losses)
> and the first factor has a bigger effect (everyone
> seems to agree a gas engine has more braking than a
> similar sized diesel) and by making the effect of

but that's my point - everyone DOESN'T agree that a
gas engine has more braking. that was my question, or
at least the why's of the difference. my diesels
always seemed to engine brake VERY well. problem is, i
haven't had a chance to directly compare two simliar
cars with different engines.

and you keep using all these numbers to say that one
thing is necessarily more important than the other,
but it seems you're assuming a lot of things, with
relation to the operation of the engines. now those
assumptions may be perfectly valid, for someone who is
familiar with the physics of it, but i, unfortunately,
am not. that is my failing, i'm not trying to blame
anyone for anything. i have a deep distrust,
especially with all the 'experts' around who like to
shove their numbers down our throats telling us that
they know what's good for us. no, this is not you i'm
talking about, just my disgust with the government and
establishment in general. this is just a long winded
way to explain that i'm a sceptic, and until i see
very well researched data that i can understand and
also doesn't baldly contradict my experience i'm
stubborn in changing my mind.

and thanks for all the info - from everyone. it's
really made me think and gave me some things to puzzle
over. (and test, once all this snow and ice goes away
- we were HAMMERED!) and i guess that's what this was
all about, anyway!

best,
erik


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