Spark Plug type for modified engine
 

I recently rebuilt my engine on my Euro 79 911SC. I used pistons and cylinders from an 82 or 83 sc with a CR of 9.3:1 in lieu of the stock 8.5:1. Also, I had my camshafts reground to that of a 911 Carrerra C2/C4 3.6L, Grind # 40. Anyone care to offer an opinion as to what type of Bosch Spark Plug I should be using?

the stock specification for that year porsche was a Bosch W5D for a Euro car.

Appreciate any assistance you may offer.

I think that you can use the same spark plugs. I do that into a 1982 911SC with 9.3:1 compression with out camshafts modification and I have no problem. I rebuilt an engine some months ago with 10.5:1 comrpession and I use the Bosch+4 4477 spark plugs. If I'm correct, is the equivalent for WR7DP. Is a colder spark plug for that engine. But if you want, try to use a colder spark plug. The heat range for Bosch and Ngk spark plugs you can find it into their internet sites.

Also, if you contact Ngk, tell to that people the engine modifications that you have and they will help you to choose one spark plug for your needs. I do that for my 911.