Date: Sun, 13 Oct 2002 10:56:31 -0500
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: High Octane was: what's the best kind of gasoline?
Content-Type: text/plain; charset=us-ascii
Clive, I respect your research and knowledge in this specific subject
area.
I was discussing Vanagons with 7.1 to 7.4 Compression ratios.
At such low compression its difficult to imagine detonation unless its
caused by lean burn that many VW owners get trying to get past rigid
state inspections.
Fuels that are sold in America are regionally blended to compensate for
altitude and season.
Fuels sold in large cities have anti-pollutant additives and fuels sold
outside the large cities have lesser degrees of these anti-polutants.
In the statement "Most detonation can be heard if you have the engine
cover off and race the engine while you're standing over it."
I make this general statement because the only detonation I've ever
encountered in about 10 Vanagons and VWs pre 85 was due to timing knock
caused by poorly adjusted points or distributor.
Although old gasoline looses some of its punch it can be blended with new
fuel and get enough octane to overcome knock problems unless you're
pulling a trailer or some other operation that overburdens the vehicles
engine.
Stan Wilder
On Sun, 13 Oct 2002 16:04:22 +0100 Clive Smith
<clive.harman-smith@NTLWORLD.COM> writes:
> >Most detonation can be heard if you have the engine cover off and
> race the
> engine while you're standing over it.
>
> Sorry Stan, totally disagree!
>
> a) Impossible to load the engine up sufficiently, although
> accelerating it
> loads it up a bit.
> b) Usually impossible to regulate rpm range under these
> circumstances, the
> transient conditions might detect an incipient pinking, but not high
> speed,
> high pressure detonation per se (what causes real damage in an
> instant)
> c) Engine unlikely to be hot throughout, I mean hot throughout,
> including
> exhaust valves and plug electrodes 'almost' incandescent.
> d) The engine will never accelerate as fast as this under driving
> conditions, so might even lead to backing off ignition off too much
> (unlikely but true).
>
> Pinking, whilst undesirable, is normally caused by (a whole
> multitude of
> things but...) overly advanced ignition (maybe just for a small
> range of
> throttle/rpm/load), carbon deposits glowing, too low octane petrol,
> poor
> combustion chamber design, plug heat range way too hot and can occur
> at low
> to medium speds and throttle settings (usually vacuum advance (if
> any) is
> the culprit at low throttle if all else to spec) and ... probably
> forget
> something else.
>
> High-speed-detonation usually results at high engine speed!, high
> throttle
> settings, and although slightly high heat range plugs can be the
> culprit, as
> can too low octane fuel - (the danger when full throttle for long
> periods),
> static advance settings combined with centrifugal advance might also
> set it
> off. Whilst carbon deposits going incandescent are normally cleaned
> off at
> these pressures and temperatures (why old granny's engine usually
> pinks when
> first blasted out on the highway), other chamber excrescences and
> irregularities including poorly seating or damaged exhaust valves do
> start
> becoming liabilities under these conditions;
> OR purely the exceedingly high pre-spark cylinder pressures (eg.
> supercharged, tuned or racing engines) can exceed the octane
> tolerance of
> the fuels;
> AND once ignited (the truly dangerous detonation) the flamefront
> develops
> unnaturally, through poor chamber design, lack of swirl and
> consequent
> stagnation, and thus local rich spots in the gas. The result is an
> explosive
> flamefront with colossal pressures generated, enough to test the
> engines
> strength thoroughly, and certainly enough to shake up the top rings
> and
> lands, loosen up any deposits which might stick under an exhaust
> valve,
> exarcebating the problem in fractions of a second - in extremis rods
> can
> bend or break (a Reno air-racing RR Merlin at boost pressures of
> circa
> 120-140 psi - if it detonates, will self destruct in a second, rods,
> crank
> bent or broken even).
>
> .. now this is the real difference between light pinking and high
> speed/pressure detonation. The former is usually the result of
> early
> ignition for whatever reason (with a flamefront that is still not at
> truly
> explosive velocities); the latter the consequences of an EXPLOSION,
> where
> the flamefront is not burning and advancing at typical speeds for
> the
> mixture, but totally out of control, at least in small pockets.
> Local
> richness might cause small detonation pockets that can do damage,
> but under
> high speed if the majority of the advancing flamefront decides to
> explode -
> you've got engine destroying detonation.
>
> Thus the latter is unlikely to occur in our VW boxer engines, being
> mildly
> cammed, untuned, low speed engines with plenty of safeguards (i.e.
> the plug
> heat range isn't that critical, cylinder filling won't be good at
> high
> speeds). Small scale detonation, and low speed, moderate load
> pre-ignition
> (pinking) are likely when everything isn't just so and should be
> avoided if
> possible, but don't usually damage the engine in a few seconds.
> Knock
> sensors are primarily for supercharged engines with mapped ignition
> systems
> that can be rapidly retarded (within a cycle or two) and those with
> a
> particularly sensitive ignition timing point.
>
> Note that one effect of a rich mixture is to effectively advance
> the
> ignition, due to its increased flamefront speed and on say,
> motocross
> 2-strokes, not an effect one can ignore.
>
> I bet you didn't want to know all that but I'm well aware that this
> is an
> incredibly complex area with plenty of room for contention - this is
> why Sir
> Harry Ricardo spent a lifetime reseaching such things, almost every
> engine
> produced in the 30, 40's and 50's using data that came out of the
> Ricardo
> labs at some time or other.
> Rather than Research Octane Number, RON ought really to stand for
> Ricardo's
> Octane Number, to salute his lifetimes work... a bit of a Brunel or
> Barnes
> Wallis - but not so famous!
>
>
> Clive
> '88 Syncro Transporter
>
> ----- Original Message -----
> From: "Stan Wilder" <wilden1@juno.com>
> To: <clive.harman-smith@NTLWORLD.COM>
> Cc: <vanagon@GERRY.VANAGON.COM>
> Sent: Sunday, October 13, 2002 3:00 PM
> Subject: Re: High Octane was: what's the best kind of gasoline?
>
>
> > If you want to hear how that motor sounds and you don't have
> anybody to
> > drive slow and lug the engine for you.
> > You can find a tall brick wall or back of a building, get as close
> as you
> > can and still open your drivers door.
> > Drive along the wall at the speed required to reproduce the noise
> you are
> > faintly hearing before .............. that noise will resound back
> at you
> > from that wall like its amplified. Works the same for noises on
> passenger
> > side you just need to leave the sliding door open to get the full
> audio.
> > Most detonation can be heard if you have the engine cover off and
> race
> > the engine while you're standing over it.
> > A good detonation test is simply to get your front wheels against
> a
> > parking stop and accelerate the van as if you were going to drive
> over
> > the parking stop. This lugs the engine pretty good and you can
> detect any
> > number of stress related noises from your van.
> > Knock sensors are a common topic on this list but most vanagons
> with
> > standard engines don't have them. I believe that they are on some
> in line
> > 4 conversion engines.
> > Be wary of any knock or ping your engine develops, it can be
> caused by
> > overheating, overworking the engine or something showing its wear
> or that
> > its going to soon fail.
> > Then to negate everything I just wrote: There are ticking,
> clicking,
> > taping, knocking sounds that are common to VW engines, I've never
> heard
> > some of these noises from other automobile engines. A carbuerated
> engine
> > will produce a complete different range of sounds that you don't
> get with
> > an injected engine. It takes an educated ear with VW experience
> to
> > identify many of these sounds and relate them to the proper engine
> part
> > or function.
> > If you suspect detonation, it can be caused by carbon build up on
> your
> > piston tops and combustion chamber. Run 16 oz of Marvel mystery
> oil in
> > your next tank of gas and possibly in the second tank as well.
> This
> > should reduce the carbon deposits. There are other products that
> can
> > perform the de carbonizing and I wouldn't discard them, I just
> prefer the
> > Mystery Oil.
> >
> > Stan Wilder
> > 83 Air Cooled Westfalia
> >
> >
> > On Sun, 13 Oct 2002 13:08:33 +0100 Clive Smith
> > <clive.harman-smith@NTLWORLD.COM> writes:
> > > High speed detonation isn't pinking. You'll not hear it at full
> power
> > > on
> > > many engines, but it'll damage the engine in seconds flat, the
> > > spark plug's
> > > earth electrode often being the first to go (with inevitable
> damage
> > > to
> > > cylinder walls/rings) , then bits off the top ring land.
> Looking
> > > for
> > > microscopic ally spatter on the plug's ceramic insulator will
> > > reveal
> > > 'incipient' high-speed detonation - always cast a cursory eye
> over
> > > your
> > > plugs whenever they are out.
> > >
> > > Pinking now and again is a different set of cylinder conditions
> and
> > > doesn't
> > > in the short term cause a lot of damage.
> > >
> > > Clive
> > >
> > > ----- Original Message -----
> > > From: "Andrew Grebneff" <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
> > > To: <vanagon@GERRY.VANAGON.COM>
> > > Sent: Saturday, October 05, 2002 8:31 AM
> > > Subject: Re: High Octane was: what's the best kind of gasoline?
> > >
> > >
> > > > >
> > > > >The key is to listen for pinging. If you can't hear your
> motor
> > > very
> > > > >well, try warming the motor up thoroughly, then take the
> motor
> > > cover
> > > > >off, and drive up a fat hill in 4th. Ping? Retard the
> advance
> > > slightly.
> > > > >No ping. No worries.
> > > >
> > > > Be careful. Just because you can't HEAR pinging, it doesn't
> mean
> > > that
> > > > it itsn't happening (ie subaudibly).
> > > > --
> > > > Andrew Grebneff
> > > > 165 Evans St, Dunedin 9001, New Zealand
> > > > <andrew.grebneff@stonebow.otago.ac.nz>
> > > > Seashell, Macintosh, VW/Toyota van nut
> > >
> > >
> >
> > ________________________________________________________________
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>
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