348 Spark plugs wires for GBP 50...

I'm making a new set of spark plug wires.

I have a couple of questions (as usual):
1) The spark plugs:
a) I am using Iridium DR8EIX's and have put about 9K miles on them. They look fine, brass brushed them and regapped. Are they up for a change or is 8k miles nothing?
b) I believe the "R" in DR8EIX stands for a resistor. Does this mean the plugs have a resistor in them to manage EMI suppression? If so, isn't the 6K Ohm built in suppression in the stock plug wires enough?
2) EMI or RFI:
a) I believe the real problem with electronic injection is EMI (Electro Magnetic Interference) and with radios it is RFI (Radio Frequency Interference), the latter being most noticeable in the AM band.
3) Plug wires:
a) I cut through a stock wire and found a copper core. This means the wires are not resistive. So they can be replaced with stock copper core wire with the appropriate plug resistance or am I wrong?
b) Can I just make up some wires with resistive cores (no resistors in the connectors) and get away with that?

Observation data:
Claim that wires are non resistive: This is confirmed by the resistors built into the plugs, 1Kohm in the coil side connector, and 5Kohm in the plug side connector. This is further confirmed by the fact the wires are of different lengths, if they were of a resistive core (resistance in terms of ohms per a given length) they would have to be all the same.
Reusable connectors: The Bosch, Beru and Ferrari caps are all reusable unless damaged. Measure the resistance between the two ends of the connector andif they are within +-5% you're good to go.

Parts:
Beru spark plug connector - part number 0300 332 110 (5 Kohm)
Equivalent Bosch spark plug connector - part number 0365 150 020 (5 Kohm)
Coil side bosch connector - part number 0356 250 033 (1Kohm)
7 Meters of copper core wire - generic parts use with double silicon insulator

 

The DR8EIX has a built in 5 Kohm resistor for EMI suppression. The leads have 6Kohm, meaning when used in series with the DR8EIX's you have a resistance of 11K0hm... Suppression needs about 5Kohm, the OEM leads have 6 Kohm which are slightly over the top. But adding the spark plugs in series - Too Much... Or am I wrong? Ferrari's original spec was for Champion A-6G's, may be crap, but were also resistor less...

Marco

 

The vendor is in Italy and a set of the Beru connectors costs about 150 GBP for 8.

I also have learnt that we have three options:
1) Expensive - use copper core wire with the resistors (to suppress EMI that can upset the ECU and engine sensors) built into the coil plugs (1kOhm) and in the spark plug end (5kOhm) for a total suppression of 6kOhm. This is to use the Ferrari specified Champion a-6G plugs (12mm thread, 19mm reach, 18mm hex, upper quartile heat-range) with NO resistor.
2) Cheaper - use standard connectors to the coil and plugs, resistive wire of a resistance : length spec to give you about 5.6kOhm of resistance for the length needed for the cylinder farthest away (1 and 8). You can refit the Ferrari rubber grommets (dust caps for the spark plug hole) and get extension adapters. You will need for all the wires to have the same length to ensure you achieve 5.6kOhm - also for a non resistored spark plug.
3) Cheaper - risky - I cut open the plug ends on the OEM plus, unsoldered/unclipped the copper core from the connector and rewelded (I melted the plastic with a soldering iron and user high temperature gasket silicone) the plugs putting in new 8mm wide copper core

Spark plugs: NGK's DR8EIX's that are excellent sport an internal 5kOhm resistor - if you fit them to the standard wires or resistive core wires described above, you will have excessive resistance, that as the plug gap widens with wear and in some air / humidity densities may cause irregularity. Not that important, but I haven't found any references to people outlining the need to match resistive plugs to non resistive cabling or vice versa, but not to double up...

Why 5.6 kOhm? this is the minimum resistance that will attenuate the EMI pulse at the power of the coil's maximum output (45kV * 2) and yet be low enough that the resulting electrode end energy differential can overcome the maximum resistance caused by the compressed air-fuel mixture (very dense).

Marco