Fw: [Vwdiesel] Diesel braking - again

[Kevin Jack]

> Ya but how many gas trucks are on the road (real trucks, not pickups).
You
> never see gas ten wheelers hauling around 20 tons. The reason for the jake
> brake is the high load. If a gas truck had the same load, the compression
> braking of the gas would not be as high as the diesel with the jake brake.
> ----- Original Message ----- 
> From: "Harmon Seaver" <hseaver at cybershamanix.com>
> To: <vwdiesel at vwfans.com>
> Sent: Tuesday, January 06, 2004 6:34 AM
> Subject: Re: [Vwdiesel] Diesel braking - again
>
>
> >    So why do you think they put those expensive Jake brakes on diesel
> > trucks? They sure don't put them on gasser trucks.
> >
> >
> > On Tue, Jan 06, 2004 at 02:46:29AM -0800, Erik Lane wrote:
> > > 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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> >
> > -- 
> > Harmon Seaver
> > CyberShamanix
> > http://www.cybershamanix.com
> >
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>