Newbie questions about high CR and twin plug conversion
 

Good day,

I'm afraid that I've been away from Porsches for way too long! I have searched on this topic, but I really don't have the 'vocabulary' to understand a lot of what I read. So, I'm going to expose my ignorance and ask a couple of questions, not hoping for 'in depth' answers, but more for general guidance and information. So, here goes...

I have just purchased a 1987 Carrera coupe, just over 100,000 miles and in absolutely superb condition.

A few years ago (some 6,000 miles ago) the previous owner converted the car from 3.2 to 3.4, using JE pistons (10.5:1 CR), cams reground to 964, and SSI exhaust.

From what I read (and the little I understand!), I learn that the 10.5:1 CR with single plug heads is problematic... tuned to be 'safe' results in less-than-optimum performance.

So (finally my questions!); what is the simplest route to twin plug conversion? Can I simply have the heads (and valve covers) modified, bolt in a JBRacing twin distributor and go... or, is there more work needed?

Alternatively, should I just change the pistons to 9.5:1 CR and forget the twin plug idea?

Full disclosure: I have the title, but not the car... Intercity will be bringing it to me in a week or so.

Thanks for indulging an old geezer!

Rob

The easy part is drilling/tapping the head and putting the spark plug in (assuming you already have the engine apart).

The expensive part is the twin plug distributor. Many people go with a crank fire or other form of electronic ignition to avoid the distributor cost. You could also do a 964 distributor. Or pay for the correct looking 12 terminal cap type.

Thanks, Flieger, for the helpful response. So, am I understanding this correctly, "do" the heads, then buy (~$1,500 + or -) a twin plug distributor and wire the sucker up... is that it?

Or, should I just lower the CR to 9.5:1 /

Rob

I'd skip the distributor and go right to an xdi system from Clewett. You can google that.

Do the twin plug. Keep the compression.

But how could you say no to this ...

http://dorkiphus.net/porsche/attachm...1&d=1395771098

We are doing this now...but very slowly. We have the 964 distributor, twin plug heads, and an Andial Motronic splitter. The Motronic can't run the twin plug by itself.