5-Series (E12,E28, E34, E39, E60)Chat relating to the BMW 5-Series of all generations. Specific models include: BMW 518, BMW 520, BMW 520i, BMW 530i, BMW 528i, BMW 530i, BMW 518i, BMW 524d, BMW 525i, BMW 525e, BMW 528e, BMW 540i, BMW 535i, BMW 520d, BMW 525td, BMW 525d, BMW 530d, BMW 525i/xi, BMW 530i/xi. (BMW 5-Series Forum)
I use the Bosch +2 from the dealer and they work fine for me. Also I did use the +4 but did not feel the difference. I guess these 4 little guys fire one by one. As such in terms of power no gain over and beyond the +2. I just could not justify spending the extra money for +4. The Splitfires are different story..again I do stick to what BMW recommend for their car.
The only advantage I can think of for the +4 is they may last longer than other regular spark plugs. this can be argued as follows:
A. less abuse for the threads on the rather fragile head threads (torque, over torque, new plugs in and old ones out etc) because +4 spark plugs may last longer they get changed less frequently. I may be wrong in all this; anyone with a better feed back is greatly appreciated
B. +4 may have a self cleaning effect beacause one electrode is firing at a particular moment since all fours don't fire up simaltanously.
Again on setting the gap some recommend to set them slightly larger to 0.86-0.91mm /0.034-0.036in to get a better idle. I am so sure about that and you may want to ask the dealer when you go for the new ones.
P.S. The above is not written on a stone and open for further discussions/feed backs
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