That may be true if the original wires are used.

But, Bosch on their own site specify their part 09027 wire set for our '72 350SL 4.5L . Almost all on-line parts suppliers sell the same wires for 4.5L M117 engines.

These wires are not copper wires, but are what Bosch call Opti-Layer Mag wires - They say it is a nickel alloy (stainless steel). These wires measure about 1.6 kohms end to end and do not appear to have any resistors built in, at least on the distributor end.

The original 1972 vintage MB wires that I just removed measure 8 kohms and have an integral 1.6 kohm resistor at the distributor end (molded into the ceramic plug) (I know - I cut one apart!)

So now we have a Bosch recommended wire set that has 6.4 kohm less resistance than the original MB wires.

So the question comes up as to which plugs to use.

I was sent plugs with following designation:

7500
0 242 235 663 -74U
WR7DC+

Old plugs, which were W7DC, also had the 7500 designation? Does this mean that Bosch consider these "R" plugs a replacement for the non-resistor plugs? WR7DC used to have 7501 number. Can anyone verify this change and explain the thinking?

If I used non resistor W7DC plugs, would my overall resistance not be lower and could this mean a very short lived hot spark? How much resistance would the 7500 WR7DC plugs add?

There are two of us with this dillema, being discussed in a separate thread. But the experts are here, so I would really like to hear any comments.

BTW, the car is running OK with new wires/plugs , but always interested in improvements!