Re: 73 super beetle rough start and smoke


"David Gravereaux" <davygrvy@xxxxxxxxx> wrote in message
news:bL-dnWhQt75WRWLbnZ2dnUVZ_vWtnZ2d@xxxxxxxxxxxxxx

<<And that would be 90.5 ron, not 87. If you can make 87 work for you,
great.
I can't. It runs hotter for me, and backing off the timing makes it bog.

you are correct on the "RON" rating..now do your homework and a little
googling and you will see that in the US we don't use that rating...it's
been discussed to death here and on every other forum you can find on the
internet....87 octane in the US is adequate....if it doesn't work for you,
you either have some engine work done(build up of carbon on the pistons can
also cause higher compression), or your tuning needs to be looked at....Mr.
Gravy, do what works for you, but be aware of what is actually
"recommended".

Jan said:
<<higher octane offers NO benefits, unless you change the engine to take
advantage of it, or if you were running too low octane to begin with.

Rule of thumb: run proper octane fuel for your engine, not less, not
more. A bone stock aircooled VW engine should be fine with the lowest
octane dishwater available at any pump, worldwide (!)


The higher octane fuels have a higher flash point, i.e. it takes more
compression and/or better spark to ignite it. Lower octane ignites easier.


modern engines rely on knock sensors and other methods to automatically
adjust for the fuel being used, and most are set up to use lower octane
fuel. Some will see no improvement when changing over to higher octane,
but some allow much more ignition advance and other ways of utilizing
the higher octane rating. Knock resistance is the key here. If the
engine performance was "restricted" by the ECU for it to be able to run
low octane, it simply removes the restrictions when you give it higher
octane.


On our stone age engines, we would have to go and manually adjust the
ignition to give more advance, and even then we couldn't easily adjust
the whole advance curve and mixture to take full benefit of the higher
octane. A modern car does these on the fly, all the time.


The biggest benefit is that with higher octane fuel, we can run higher
compression. If you are able to compress the fuel more before igniting
it, AND ignite it in a controlled manner, you will get more power from
the same amount of fuel. Sadly, this means tearing down the engine and
changing some fundamental parts of it's design.


For the reason explained above, I never build high performance engines
to use low octane fuel. It defeats the purpose; why optimize everything
else for better performance, and then go backwards with the fuel? :)


OLD and worn engines, then... they often have massive amounts of carbon
buildup in the combustion chambers and on the top of each piston. This
residue promoted knocking/pinging/detonation, which will eventually
destroy the engine. If you are experiencing symptoms or signs of it,
like dieseling after you turn the engine off, you should switch to
higher octane fuel just to see if it has any effect. It is more
resistant to self-ignition as I already explained. If the symptoms
disappear, you can assume you had buildup glowing red hot in the
chamber. You can then safely continue driving the car with the higher
octane, and now take some longer highway trips in it, burning off the
carbon deposits. Now is a good opportunity to also eliminate the root
cause of those deposits: a tuneup and mixture adjustment is in order.
Then after a month or so, go back to "as high octane as necessary" for
your engine.


Jan >>>>


.

Relevant Pages

  • Re: Shell "V-Power" petrol
    ... Compression is directly related to power (see engine tuning), ... that require higher octane usually deliver more power. ... ratings of the fuel... ...
    (uk.rec.cars.maintenance)
  • Re: Gasoline grade BTUs per gallon?
    ... To me efficiency is power out/power in. ... Engine efficiency is a function of compression ratio (peak ... Lower octane fuel "pings" or detonates instead of burning ...
    (sci.energy)
  • Re: race fuel question
    ... impact or its bearing on engine durability. ... science of octane. ... the compression without detonation. ... In general a higher octane fuel has _less_ energy content and burns ...
    (rec.autos.sport.nascar)
  • Re: OT: You know youre from California if...
    ... >>1)VW device advances timing until knock detected and backs off one tick. ... >>combustion cycle irrespective of the amount of octane you throw at it. ... need for higher octane gas. ... higher octane fuel does not have more energy ...
    (sci.electronics.design)
  • Re: Website
    ... engine, the effective octane requirement would be lower, not higher. ... properly with "regular," going to a higher octane does nothing but waste ... The car, any modern car with ...
    (rec.outdoors.fishing.fly)
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