diesel valve springs

[drew@dyermaker.cs.uoguelph.ca (drew)]

My cam profile assumption is based on the fact that diesels function with
maximum cylinder filling of intake air.  The air to fuel ratio varies with
amount of fuel injected (100:1 ish at idle to maybe 20:1 at full power)
but the cylinder is always filled with the maximum amount of air possible,
which allows more fuel to burn, makes more power, and produces less smoke.
A normally aspirated diesel pumps the same volume of intake air per
revolution at idle as it does at rated speed, or with your foot mashed to
the floor.  A turbocharged diesel will pump a greater volume of air
because the turbocharger will have pressurized the intake air to allow a
greater mass of air to fill the same cylinder volume.  This is why
turbocharging is popular with diesels - it forces more air into the
cylinder which in turn can allow for more fuel to be injected, making more
power.

Although ~some~ automotive diesels have been throttled (older mercedes
comes to mind) to aid in engine braking, diesels in general, and
definitely VW diesels, are NOT throttled (that is to say, there is no
restriction of intake air.)  Diesels are "throttled", or regulated, by the
injection of fuel into the cylinders, which are always filled with as much
air as possible.  The cam profile will support this by having a lift and
duration which will allow the engine to "breathe" as freely as possible.

Hope you enjoyed the fireworks.




On Thu, 4 Jul 2002, Larry wrote:

> Drew-
>   What leads you to believe a Diesel has a more radical cam profile?  I
> can't say it doesn't, but if that IS true, then the valve springs may indeed
> be of a higher rate than the gassers.
> But, somehow I don't buy into that; since a radical cam only benefits an
> internal combustion engine at "higher" rpm, the Diesel, with its lower
> operating rpm, would seem to be better suited to a milder cam (and visa
> versa).
> BTW, the Diesel engine is throttled. You may have been thinking of something
> else....
> I'm off to watch the fireworks....
> 
> Larry
> 
> 
> 
> 
> ----- Original Message -----
> From: drew <drew@dyermaker.cs.uoguelph.ca>
> To: Larry <rocco16v@netzero.com>
> Cc: Lisa Lutman <llutman@hotmail.com>; <scirocco-l@scirocco.org>
> Sent: Thursday, July 04, 2002 5:23 PM
> Subject: Re: diesel valve springs
> 
> 
> >
> > I'm not sure what you mean by milder state of tune overall, but yes,
> > diesels do generally operate at lower rpms than gas engines.
> >
> > As far as spring rate goes 1.6 NA and TD motors do use different inner and
> > outer valve springs than the 8V and 16V gassers.  As to spring rate, I'd
> > have to go out to the shed and squash a few and compare them...  :)
> >
> > My guess is that due to a more radical cam profile (in part to support the
> > 23:1 compression ratio of the indirect injection VW diesels) the diesel
> > springs may well be more durable than their gasser counterparts. Somewhere
> > I had diesel cam profile information, which I have misplaced, but there
> > has to be a good deal of lift to maximize the amount of air in the
> > unthrottled diesel's cylinders.
> >
> > If I find any data to support this theory I'll post it - in the meantime
> > it's just conjecture.
> >
> > Drew
> >
> > Drew MacPherson
> > '84 Wolfsburg Edition Scirocco TurboDiesel
> > '99 Vento TDI
> > '87 Jetta GLI pretender winterbeater
> >
> >
> > On Thu, 4 Jul 2002, Larry wrote:
> >
> > > I don't have any specific knowlege, but would think this would NOT be
> the
> > > case.  I base my opinion on the fact that diesels generally are a much
> > > lower-rpm (actually in a milder state-of-tune overall) engine than
> gasoline,
> > > and have no need for stiffer springs(or springs that are even equally as
> > > stiff..)
> > >
> > > Larry
> > >
> > > > I've heard that you can use diesel valve springs in a VR6 when doing
> cams
> > > > and that they're stiffer and cheaper than aftermarket ones. I'm
> wondering
> > > if
> > > > this can be done on a 16v if I put a 260/276 cam set up in my 2.0L.
> Anyone
> > > > know? TIA...
> > > >
> > > > Lisa
> > >
> > >
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> >
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Drew MacPherson - '84 Wolfsburg Edition Scirocco TurboDiesel