Twin spark

[per oiestein]

Hello
I am going to uppgrade my 911 to twin spark.
I heave a friend that is an cnc operator and we are trying to find the speks.for how to drill the second sparkplugg hole in the head.
Is there anyone on this forum that can help us with the angle or teknical drawing of the head with twin sparkplugs.

Best reguards from Norway.
Got our firs snow today so it is time to build porsche engine.

Per Oiestein

[neilca]

This is a good question, anyone have a drawing showing the angle and location?

[prschmn]

Pardon me but as someone who does Porsche machine work for a living---
You probably should expect those who have spent countless hours developing methods and measurements to share an awful lot. If your frined is competent the two of you will be able to come up with a plan.

[tadd]

Hi. Did you get my pm? If you would like more detail, feel free to email. Here was the jist...

Adding the second plug is not hard. Look up 'DIY twin plug' - a good read. I've done several sets over the last few years on a Bridgeport series I. I turned a rod to 3/4 for a collet on one end and 14x1.25(IIRC) for the plug on the other. About 7-8" long. you will also need a plate with four holes for 'head studs'. I chuck the head hanging from the collet and rotate the quill so the head sits square on the table and clamp. Remove plug fixture rod. Unbolt head, rotate 180*. translate table 0.4" to move the 2nd plug back towards the exhaust. If this is a 3L head your good to go. First cut is a 3/4 inch end mill if you go with the 12mm plug. The 'Y' series Bosch is 16mm on hex, so you'll need a second pass with a larger end mill - just don't go as deep as the Plug seat. Finally get some canning wax from the food store and instead of melting between the fins, beat it in with a plastic mallet. Pack it on good, otherwise you'll break fins. Heads need to be clean or the wax will work out as you cut. If you are doing 2.0/2.x heads you need to add an additional 0.7-0.1" translation (in/out) to move towards the head center. There is less metal and this gives a full seat with no breaks. Enjoy! BTW, it's nerve racking on the first set!

[neilca]

Thanks Tadd,

That is a great tip using the wax. I think I will try it on some scrap heads first.

[per oiestein]

We need more data if anyone can help us.
Got a message from a German mechanic that Porsche used mm plugs even on the second set.
Heave read on the forum that they user mm.
Any documentation out there?

[per oiestein]

Lost 12mm and 14mm

[JohnJL]

Best to see if you can borrow a twin-plug head from someone and take measurements/comparisons from that.

[cgarr]

I set my mill at 12.5 and 23 degrees as far as angle then use my jig to position the new plug hole in the correct position. Use a ball end mill for the initial cut depth then finish with a end mill and you won,t get any fin chatter or damage. I only do 12mm plugs to leave more material.