As Bosch no longer manufactures the non-resistor version of the W9DC and W8DC, I did some research and came up with the following cross chart. The thing I found most interesting was that different manufactures heat ranges do NOT match - some have more overlapping ranges than others. So in the chart below, the plugs are all arranged from HOTTEST (top) to COLDEST (bottom). As such, it is up to your judgement as to going a little hotter or colder on a plug.
In making that decision: A HOTTER plug will run cleaner, but may cause more detonation/preignition/pinging. A COLDER plug may be more likely to become fouled with carbon deposits, which will then lead to misfires.
THE CHART
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I also found the following links to plug temperature ranges and selection that you may find useful:
From NGK's learning center:
General Information on Heat Ranges
NGK's heat range conversion chart
Interesting discussion on reading plugs for race tuning:
Wallace Racing - Spark Plug Reading
And a page with the minutiae of spark plugs:
Stealth 316 - 3S Spark Plug Information
In making that decision: A HOTTER plug will run cleaner, but may cause more detonation/preignition/pinging. A COLDER plug may be more likely to become fouled with carbon deposits, which will then lead to misfires.
THE CHART
I also found the following links to plug temperature ranges and selection that you may find useful:
From NGK's learning center:
General Information on Heat Ranges
NGK's heat range conversion chart
Interesting discussion on reading plugs for race tuning:
Wallace Racing - Spark Plug Reading
And a page with the minutiae of spark plugs:
Stealth 316 - 3S Spark Plug Information
Added 10/23/2014
