HKS Spark Plugs for BMW S65 (E9X M3)(Requires tune to clear engine knock code) used for about 4000 miles, new are $25 each.
Gained 3-4HP on the dyno on a hot day!
These plugs are "colder" than the stock plugs, allowing the engine to keep full timing up to redline without pulling back due to heat!
$50 +$5 ship
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