[Public-List] Old gas engines

[Gordon Laco]

Y'know - I never really understood what Octane meant.

Thank you very much Stephen!

Gord #426 Surprise


On 31/08/10 3:05 PM, "Stephen Gwyn" <gwyn at beluga.phys.uvic.ca> wrote:

> 
> Hi,
> 
> Just a quick note to remind people that for gasoline
> "high octane" = "less flamable" not "high power".
> 
> The point of high octane fuels (running from higher octane
> automotive fuels or aviation fuels like 100LL to jet fuel and
> highest octane of all, diesel) is not that they burn hotter, it
> is that they don't ignite prematurely in high compression
> engines.
> 
> In such engines, the increase in temperature of the fuel-air mix
> as it is being squeezed on the compression stroke can ignite low
> octane fuels before the spark plug fires, causing knocking.
> Tetra-ethyl lead was used as an anti-knock compound, decreasing
> the spontaneous ignition temperature of fuel. It is amazingly
> poisonous, (you know, lead poisoning, except now it's in the air
> you breathe) so it has been taken off the market except for
> limited amounts in aviation fuel (LL in 100LL stands for Low
> Lead).
> 
> The Atomic 4 is not a high compression engine, and older (is
> there any other kind) engines in particular usually have fairly
> low compression. If you want your A-4 to run well, use low octane
> fuel. If you use high octane fuel, it will burn poorly since it
> won't be at its correct temperature when the spark goes off,
> causing decreased performance and increased fouling to due
> incomplete burning.
> 
> If you want high octane fuel, you can always use diesel,
> which has a very high octane rating.
> 
> Stephen
> #495 Quasar
> (with a smooth running Atomic 4)
> 
> 
> 
> 
> 
> Still scraping by with the A4, while rebuilding the carb on the
> dock I met a lot of other people having engine troubles recently.
> I had a friend who is also a mechanic helping me.  He suggested
> the reason so many people are and will have trouble with older
> gas engines is the gas itself. These engines were built to run on
> leaded gas, the lead in the gas acts like a lubricant. The low
> grade gas at most fuel docks also has ethanol in it which would
> do just the opposite. You can purchase a lead additive from most
> automotive supply stores and if you can't bring in your own high
> octane fuel there is another additive to deal with the ethanol.
> Can't remember the name - it's blue.  These changes made an
> improvement in my engines performance. Thought I would share
> incase others are/were in the dark about this.
> 
> 
> 
> ------------------------------------------------------------------
>   Stephen Gwyn                 |  Tel: 1-250-363-3136
>   Dept. of Physics & Astronomy |  Fax: 1-250-363-0045
>   Univ. of Victoria            |  Cell: 1-250-885-6969
>   PO Box 3055                  |  E-mail: gwyn at uvastro.phys.uvic.ca
>   Victoria, BC  V8W 3P6        |  http://orca.phys.uvic.ca/~gwyn
> ------------------------------------------------------------------
> 
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