re: Bosch +4

[tedcrum@xxxxxxxxxxxxxxxxxxxxx]

I put them in my 1980 528i, and the engine idles much better now.

The  injected Big Six has always had a lean surge problem, and such
problems are often helped by a longer spark. BMW addressed this with a
service order increasing the plug gap to .8 mm, but they were unable to
call for a bigger gap because of the limitations of the ignition system.
They called for the silver plugs in the same service order, I suspect
because they wanted to gap reduce erosion and further stress on the
ignition system.

A semi-surface discharge plug like the +4 can produce a longer spark with
the same voltage. The Lodge Gold plug of the 60's use that technology, and
Alfa Romeo instaled them at the factory in about '75 to get their
lean-running cars through smog.

They probably won't help cars with high-energy ignition, but they beat the
Silvers in the Big Six.


- -Ted Crum
 1980 528i

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