Short answer: go ahead and use regular unleaded.
There are two issues here- valve seat recession and fuel octane rating.
The main problem encountered when using unleaded fuel in an engine designed
to run leaded fuel is an effect called "valve seat recession". The
tetraethyl lead present in leaded fuel serves as a lubricant on the
interface between the valves and the cylinder head. If your cast iron valve
seats are not hardened and you use unleaded fuel in your new engine the
valve seats will wear away pretty rapidly, the valves will sink into the
head, and the engine will run progressively worse until a valve is burned
out or something else breaks.
In general engines built from the mid-70s on have hardened valve seats, as
do engines designed before the widespread use of lead (1930s? not sure). A
lot of engines built during the lead years have cylinder heads that work
just fine with unleaded fuel. Engines which ran using leaded fuel for many
years and have been switched over to unleaded will also be fine- the valve
seats have been coated/embedded with lead and can now tolerate unleaded
fuel indefinitely. If you rebuild an old engine and chemically clean the
cylinder heads you should have the machinist install hardened seats (at
least in the exhaust valves) to prevent the problem.
If you have a British car you can get in touch with Practical Classics
Magazine (UK) for a list of classic cars that are OK with unleaded. Britain
just recently banned most leaded fuel sales so the issue is still fresh for
The other issue is octane rating. If the fuel additives you have been using
also raise the octane of the fuel (this was the main function of lead!) and
you have an engine with a high compression ratio then your friend is
correct- you will need to use premium gas. Find out what octane rating your
car is supposed to use and stick with it.
At 10:03 AM 5/4/2001 -0500, Eric Schulte wrote:
>I've been using lead additives in my Regular gasoline that I burn in my
>older cars (1934-1955), with the understanding that the modern unleaded
>gas does not have the ability to protect the older valves from damage.
>Recently a friend told me that this is unnecessary to do if you run
>premium gasolines. Is this true?
>Skeptical, but ready to listen,
Erik Quackenbush, V.P. Operations, Midwest Filter Corporation
1-847-680-0566 fax: 1-847-680-0832 http://www.midwestfilter.com
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