Well, not all of us have 6 cylinder engines. So, for me, it would be $56

I am in the 100k mile camp. The modern ignition systems can compensate for the larger gap due to wear with nary a performance issue. I suspect any improvement from 25k mile plugs is a placebo affect or you have something else wrong with the engine causing plug damage. After 100k miles or so, the coils have to work harder to jump the gap and you will start to get coil failures.

Just my observation over the many years with many different BMW engines.

 

If you think changing your plugs at 25K miles is gonna "improve the over all performance" of your car...you're wrong. But if it makes you feel better...then by all means do it...kinda like people who change their oil every 3000 miles...a complete waste money.

 

The issue I have with this thread is the OP's comment they are free if you just take them back when you fell like it and tell them they are bad. People like this cost the rest of us more money :thumbsdown:

 

+1

 

+2 Unleaded gasolines, much-improved spark plugs, fuel management & fuel injection systems, and ignition systems have extended the normal life of spark plugs well beyond the OP's recommended 25K miles.

 

if you use good plugs like NGK, you can actually increase performance, too. but, they have a very short lifespan of about 10k miles. i changed my plugs annually on my Z28.