Gerry Davison wrote:
>The lab boys at Shell informed
>me a long time ago that they first began to put lead in gasoline in 1948.
>Prior to that, gasoline had an octane rating of between 60 and 80 and had
>no additives. Therefore engines built before 1948 ran exclusively on un-
>leaded gasoline.
Richard Notton wrote:
>As a matter of interest it was Mr Pratt and Mr Witney (Dependable Engines)
>that first started adding tetraethyl lead. In one of the first radial
>engines, developed on govt. money, there was a design fault that caused
>both valve failure and low power output vs poor consumption owing to
>necessarily rich running, the lead additive was the cure-all. We followed
>suit when the Merlin was found to be a trifle short of grunt vs the FW 190,
>in this instance the lead content was raised to allow more supercharge/revs
>with no detonation viz., open the throttle more! The lead content then
>used, and maybe still is, in AVGAS 120 octane was some 20 - 50 times that
>in pump fuel!
I've been reading up on the subject lately and a good source, among others,
is a chapter on the subject in Dr. Ulrich von Pidoll's book "Kaefer: Ein
Auto schreibt Geschichte" (Hamburg: Nikol, 1996, ISBN 3-930656-36-1).
Basically, Gerry and Richard are right. Indeed, lead was not added to car
petrol until after WW-2. Also, during the war, when the race for higher
power output from aircraft engines was in full swing, it was found that by
adding lead to petrol the octane rating could be raised (i.e. petrol became
more resistant to spontaneous combustion). Thus higher compression ratios
and supercharging became possible.
After WW-2, increased power output for car engines was also solved by
raising the compression and the revolutions per minute. Adding lead again
solved the pre-detonation problem (although up until the 1960s other
additives were also used for this purpose). The advantage of lead additives
is that after being burned, they act like a solid lubricant on the exhaust
valves and seats, and thus reduce the amount of wear over a given period.
(The process is comparable to the use of white metal in engine bearings.)
Now that leaded petrol is being banned (for our own health), what can we do?
1) fit induction hardened valve seats and valves when rebuilding the engine.
This is recommended by the Dutch Federation of Historic Car Clubs, as the
cost of hardened seats and valves is only slightly higher than non-hardened
ones, and is simply the most durable solution.
But what if we have an engine which is not yet due for a rebuild?
2) Dr. Von Pidoll quotes a 1986 SAE technical paper. A number of SAE tests
(incl. one on Army vehicles) proved that the wear on valve seats and valves
with unleaded petrol is not noticeably higher (compared with leaded petrol)
if the engine is operated under 3,000 rpm.
My own opinion is that this is a good tip, as 1940s and 1950s MV engines are
rarely operated above 3,000 rpm. over long periods. It is also confirmed by
Gerry's test:
>I run a Dodge WC51 from 1943, have had it 3 years and run it on unleaded
>gasoline without any problems whatsoever.
I'd like to hear from anyone who can add to and/or correct this.
Hope this helps,
Hanno Spoelstra <H.L.Spoelstra@WbMt.TUDelft.NL>
Bloemendaal, The Netherlands