Bosch spark plugs: WR7DC vs W7DC - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 02-13-2010, 06:05 AM Thread Starter
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Bosch spark plugs: WR7DC vs W7DC

The other day I ordered some spark plugs for my 3.5 with transistorized ignition. I got some Bosch WR7DC instead of the original W7DC. What does that "R" stand for? Is this what they call integrated resistor plugs? Is it OK with the transistorized ignition or do I risk to fry something? The car works OK, even if it seems to be a bit less responsive at mid and higher ranges. But I don't know if this is the cause as I worked on several things at the same time.
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post #2 of 3 (permalink) Old 02-13-2010, 06:16 AM
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If yours is like my 72 280se it has resistor ends on the wires, so you need to use the non resistor plugs if you can. Without the R. However I have been using resistor plugs because I didn't know any better.
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post #3 of 3 (permalink) Old 02-16-2010, 12:50 PM
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It shouldn't have any ill effects
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