I agree, the wires seem to add a lot of clutter to the otherwise beautiful engine. To resolve this I’m going to run the wires horizontally under the intake manifold and then up the engine V from the rear, vs over the cam cover. (To facilitate this I’ll be using a cap which has the wires come in horizontally. )
Once they enter the V, I’m using a chrome spark plug lead conduit from an Aston Martin DB5 vs the Jaguar cardboard one.
Here’s a link to an old thread that discusses this:
7mm seem to be the standard as others have said with the carbon not Cooper center core
From Aston to Ferrari and Jaguar
It seems to be it
Ps use prep sol to take off the white lettering
All my 123 has been 7mm, you could use 8 but I think that you might have an issue with original radios and static to a degree.
I think either would be fine though…
gtjoey1314
My 1950 120 OTS would have had its HT leads routed around the back so during its restoration I put it back to this original specification. I’m unsure as to why Jaguar made the change but in case it was due to excessive heat creating breakdown of the insulation I routed them through an aluminium tube with a calcium silicate sheet between the tube and the engine for additional heat insulation. Cross firing between leads has also been suggested as a reason for the change.
For long term reliability my preference has always been for solid copper core leads with non-resistive plug caps but this arrangement will certainly radiate into long, medium and to a lesser extent VHF/FM radio transmissions. Not sure about the USA but in the UK, digital radio (DAB) frequencies typically all above 175MHz are unaffected.
Of course choosing this route may well cause interference to others using older radios and feasibly upset some not so well screened electronic control systems on modern cars which could be fun.
As you can see from the following photos, there is no doubt that re-routing improves appearance.
Bob, I do not know about reliability, but for best ignition, there should be a minimum of about 100 ohms resistance in each wire. It allows for better extension of spark. For radio, suppression, yes, probably 1000.
Tom
On my 3.8, this is the way they were originally arranged, in a PVC sheath coming up between the cam covers. These are the original impregnated cloth covered wires that were fitted at the factory and they never gave any problem (and with points ignition too).
They used copper wire with which they were secured to the screw-in distributor cap terminals where the wire was splayed out behind a copper disc.
If you are using original conduits, the only size that will work is 7mm. Otherwise, 8mm or larger is mostly about better insulation, it won’t create radio interference as long as it has a suppression core. The larger diameters may also have thicker conductors, but that really doesn’t make much difference for street performance.
