Twin Plug DIY?

[Bob Goding]

Keep going boys--I have been thinking about this for quite a while but a sacrificial head is pretty scarce round these parts!
.I like the idea of a smaller dia.spark plug
might be able to run the lead thru a smaller hole in the cover, But I guess the plug tool would dictate that.

Bob
76 & 77 2.7's

[David]

I've just about finished the first head. After starting to machine through the fins I decided to go with the 12mm plug. It was just too scary cutting with an endmill large enough for the 13/16" socket. I cut the pocket with a 3/4" endmill and then followed with a 1" endmill to make room for the 5/8" socket. I should be set up to crank out the remaining 5 pretty quick. Then I'll change the set up and relieve the combustion chamber side with a ball end mill.

Is it worth the trouble? NO, I don't recommend this as a DIY job. Every cut I make makes me feel like I'm taking the final critical cut on something I've spent 20 hours machining.

As for the plug wires, does anyone know a source for matching plug wires to fit the 14mm and 12mm plugs?

[Grady Clay]

David,
You are right, this is not a DIY process.

Now that you are set up, fill the fins with wax to prevent vibration.

Best,
Grady

[Steve@Rennsport]

David:

You can use the Beru, Bosch, etc ones (I prefer Magnecor 8.5mm wires & connectors) as they fit very well on all those 14mm and 12mm plugs (W-series Bosch/B-series NGK and X-series Bosch/D-series NGK)) that you might use with a 13/16" hex. I've used them on all twin-plug motors for 25 years. I also use plug retaining clips on the lower 6.


They do not fit well on the 5/8" plugs (FR5DTC) that the 993 uses,.....

[David]

EDIT: Grady, thanks for the wax tip, it works great.

[Grady Clay]

Steve, David,

There is a nice short Beru (resistor and non-resistor) connector where the wire is 90 deg that will fit a 12 mm sparkplug. The great part of this is it fits under the lower valve cover!

Once you have a twin plug that is all settled in and you rarely have to change plugs, this is a great solution for a street car. The connectors and wires are all protected by the valve covers. Yes, to change the plugs you have to remove the valve covers. That can be a pain. However with a good running engine it works great. It keeps the wires and connectors out of the debris and water path from the rear tires.

If you want to appear original single plug, this hides the second ignition.

You would not do this for a track only/race car.

Of course if you want to show off your twin plug installation; long connectors, bright retaining clips, and bright red/yellow wires work great.


Best,
Grady

[David]

After putting wax between the fins things went very smooth. Here's a few pics:

[David]

Here's some pics of the ports where I opened up the intake for the Carrera intake and the smooth plug for the exhaust air injection:

[Grady Clay]

David,

Beautiful work.
The Factory machinists would be proud of you.

Best,
Grady

[TimT]

Nice....

[David]

Thanks for the compliments.

After looking at the new holes for a while, I think the 12mm plug is the way to go. The combustion chamber pocket is so much smaller and I sure don't need any less compression.

[Scott Wolthuis]

Originally posted by Grady Clay
Steve, David,

There is a nice short Beru (resistor and non-resistor) connector where the wire is 90 deg that will fit a 12 mm sparkplug. The great part of this is it fits under the lower valve cover!

Once you have a twin plug that is all settled in and you rarely have to change plugs, this is a great solution for a street car. The connectors and wires are all protected by the valve covers. Yes, to change the plugs you have to remove the valve covers. That can be a pain. However with a good running engine it works great. It keeps the wires and connectors out of the debris and water path from the rear tires.

Best,
Grady

Grady, do you or anyone else have pictures or more information on the above-mentioned set-up. Pros/Cons?

Thanks
Scott

[asphaltgambler]

Hey what's that guy doing in my garage??

[beepbeep]

Very nice! What EFI is going to be used?

[911pcars]

Sorry, I couldn't resist the urge for a commercial plug (no pun intended).

These work well to prevent the spark plug cables and connectors from melting. Exhaust tubing surface temps are right around 400 deg. F.

This is a pic of Thom's 3.6 but they work fine for all 911s.


Sherwood

[David]

I've been moving pretty slow on this project. Hopefully I'll get the cams in and seal it up this weekend.




New parts:
Carrera intake
Autronic ECU for injection and ignition
Autronic CDI to fire 6 waste spark coils
Twin Plug (still haven't looked for wires for 12mm plugs)
Three angle valve job with new valves, guides, and springs (done by EBS)
JE 3.4l, 7.7:1 CR pistons
Pauter rods
ARP head studs
Patrick lightweight flywheel
Centerforce aluminum pressure plate
8:39 r&p
a ton of expensive odds and ends

Existing parts (installed by PO):
K27 with 1 bar wastegate spring
B&B exhaust
B&B dual outlet muffler ( I may build a stainless open pipe exiting on the right)
B&B intercooler (I may get a custom large intercooler to fit the Carrera intake)

[Jim Richards]

Originally posted by Scott Wolthuis
Grady, do you or anyone else have pictures or more information on the above-mentioned set-up. Pros/Cons?

Thanks
Scott

I was wondering about this, too. My parts are on the way to the machine shop and we have been talking about twin-plugging the heads and valve covers. I'd like to nail down my approach ASAP. I'm already thinking of 12mm.

Ooops. Might be a thread hijack in progress.

[914timo]

David, just curious, what kind of wax did you use between the fins ?

[David]

I used Gulf parifin wax from the grocery store. I guess it's used for canning. I used some clay to block off the ends and the head bolt holes and poured in the melted wax.

[MotoSook]

Very nice work David. Very nice!