which spark plugs for a 76 450SL?

[speedy72t]

I ordered new plugs from german auto parts for the benz and they came in as WDC8 (I think that was the right lettering) but what I pulled out was WDC9. Once upon a time I knew the answer to this but is that a different temperature plug or just a different factory pre gap? the plugs came out clean but some of them had a gap of almost 1.2mm! pretty serious gap to the .77 or so that the Haynes manual shows.

Thanks for any help

[jr6700]

different temp range....but also 75-76 is a split year
M117.985 -021837 W9DC0
-003635 W8DC0
-003634 W7DC0

[speedy72t]

Well I haven't actually looked at the engine to confirm this but according to the build card my engine is 117985 12 001649 which I believe puts me in the W7DCO range? I don't exactly understand your numbers though. The way I read it if the engine number under 021837 down to 003635 then it is W9DCO, if it's exactly 003635 then it is W8DCO and if it is less than 003634 then it is W7DCO.

Anyone have any more input on this? Why where the changes in spec made? What's the proper gap and will this one range seriously affect the efficiency of the motor?