by Jim Thompson
|Bosch Spark Plug Numbering System
(at least here in the US/Canada):
|Old Bosch Part #||Revised #||Latest #|
Note: "LATEST #" designations are the latest Bosch Marketing numbers being phased in here in the US. I've seen these numbers on skin-packed plugs at places like K-Mart, Target, Wal Mart and some FLAPS. Use to be you could tell the heat range of the plug by it's Part Number (W8 being hottest, W4 being coldest) but with this new system, you can tell anymore without a scorecard. I continue to list and sell 'em under the "W" Part Number.
W8's are hotter running plugs for most normal driving conditions as well as colder climate and lotsa stop n go traffic.
W7's are colder running plugs for warmer climates and extended/high rpm highway driving. Usually the plug of choice when building those hi-perf motors as well because they tend to run a little hotter than stock.