[Public-List] Old gas engines

[Stephen Gwyn]

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.



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  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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