VAC Recommends that you replace your spark plugs in these
Classic 'M' engines every 15-20k miles depending on use.
Direct replacement plugs for the S14 and S38 found in E30 M3,
E28 M5, E24 M6.
Also used in some BMW motorcycle models.
VAC Tech Tip:
We recommend these plugs for many s14 engines up to about 250BHP
depending on your fuel used and ignition timing.
For max performance street and mild race engines up to about
310BHP, we recommend a race plug like the Bosch XR4CS plugs
is currently empty