Re: Bosch +4 Plugs (archive)

My question is, who has used the bosch +4 spark plugs and what were the results? I need to replace my plugs soon and was wondering if I should get them. TIA
Jim Eagan
83 533i 424,000 miles

I run them in my '86 535i w/195,000 miles. I have had decent results with them but I know subtle differences in my cars pretty well. One cannot expect the world from a spark plug update but the 4's do have an advantage.

Have you ever wondered why some cars like the high end Porsches run dual plug cylinders??? It is because it will burn the fuel mixtures more evenly and cleanly. One fires in one place starting the burn from one side and then the next round is fired by the other plug. Thus a cleaner combustion chamber and a more consistant running engine. The plus-4's are a poor mans way to accomplish about the same thing. The spark will always fire at the terminal of least resistance and then dance around the terminals thus moving where the burn starts. Of course it may fire 5 times at the same terminal and then start moving around.

One more related item, I also don't use regular Bosch platinums. The small platinum electrode in the ceramic tends to burn down thus widening the gap. when one gaps the plug they think it is normal but the gap is longer because the electrode is burnt down into the ceramic. This really plays havoc on turbo cars given the extreme combustion pressures....in other words it fires only when it gets lucky and you have one crappy running engine.....

Mike H

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