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My 67S with the stock ignition came with the Bosch W5DC spark plugs when I got it, but the documentation talks about the W3DPO. I now need to replace them and was wondering what to get.
I am also thinking about switching to a CDI unit. Would that change the choice of the plugs?
Behyar
Hi:
IMHO, the W3DPO plugs are too cold for these engines unless they are being driven flat out for a long time.
You can get away with those plugs if the car has an MSD ignition system and matching coil.
I would use W5DS with either ignition setup for all-around usage and W4DS for track use. These are silver plugs and have a very wide heat range.
I cann't seem to find the Bosch silver plugs anywhere. They must have been discontinued. What is the downside of running cold plugs beside the big price difference?
Running plugs that are too cold for the application results in poor running and a loss of power.
The silvers are usually a special order and few outfits stock them. Its a real shame as they are really better than the old style platinums (DPO).
If you cannot find them, please e-mail me directly and I'll get you a set.
I couldn't agree more. I've used nothing but the silver plugs for years. THey last longer than the old platinums, and cost much less. I've not tried to buy any for a while, so if they are becoming hard to get, please let me know where to find them!
Relative to the heat range (W3, W4, etc), that's independent of the electrode material. I also agree that a W3 is a bit cold for anything other than racing, but I would probably not go beyond a W4.
Lee