באמת קשה לחפש בגוגל...?
....The Unites States and most other countries switched from leaded to unleaded
fuel years ago. The lead additive, tetraethyllead, retarded "preignition"
in gasoline engines. Preignition causes engines to run rough, and to not
shut off when the key is turned off. The suppression of preignition is
measured by the gasoline's "octane rating". A good high-octane gasoline
allows a standard engine to run smoothly. Leaded gasoline also protected
some older car engines from wearing down by covering soft engine parts with
lead-containing material.
--------------------------------------------------------------
....Lead was used in fuels as a lubricant and octane (energy level) booster.
However, we have developed other less dangerous chemicals to use in it's
place in fuels. Gasoline still includes a tiny amount of lead because of
the natural processes under which oil formed in the ground, but we no longer
add lead to fuels in the United States.
-----------------------------------------------------------------
Lead has not been in gasolines for use for years mainly because lead
pollution affects living cells and health, especially in children. Lead
was added to gasoline as a liner for cylinder walls in a compression
engine to smooth the effects of metal rubbing metal. It is abundant and
cheap. Now other chemicals are used.
-----------------------------------------
והרי לך התשובה המלאה.
עריכה: אני מניח עכשיו שאתה מסוגל להניח למה מנוע שתי פעימות צריכים דלק עם עופרת(פעולה יותר אלימה של המנוע ופחות ידידותית לצילינדר)