Rotor Arm Mod
Also known as the "NOSWizard mod", because it was first described by the NOSWizard. It aims to increase the strength of the spark by 10-20%. It involves scrapping the inline resistor that lives in the rotor arm. (Click for larger images)
Below is a new rotor arm intact. The resistor is within the black bit.
Scratching the resistor reveals a lot of the stuff:
I used a Dremel with an engraving tip, but other tools might do the job:
Below are two rotors - one is stock with the whole resistor, to the right is the modified one. It's filled with solder, effectively short-circuiting the two copper ends.
The stock rotor measures 1KOhm between the two ends. The modified one is practically zero Ohms.
This has to be done with attention to detail because it rotates at half the engine's speed, which is a few thousand rpm. If it's not secure it might disintegrate, leaving you with a weak (or none at all) spark. Also try to use some epoxy resin to cover the lot, in the manner the OEM item does it. Good quality solder has a resin in the core, which floats to the surface once molten - but add more if it doesn't look enough. This will prevent the air within the cap from becoming ionised (used to be a source of inexplicable intermittent faults in older automotive designs). Better safe than sorry.
Be careful to measure the resistance afterwards, and verify that it's zero (or thereabouts). If the copper ends are not electrically connected, then the resistance will be infinite, of course. The car may still run though, as the spark can jump a few millimetres - but it will be weak, and under boost it will misfire.
This is a no-nonsense mod. The car feels stronger and smoother at full boost - no question about it. It also appears to pull cleaner through the whole rev range, an effect similar to advancing the ignition timing by a few degrees. I can only think of two reasons that this could happen:
1. Without the resistor the coil now discharges slightly quicker.
2. Without the resistor the spark duration is now slightly longer, increasing the chances of finding an ignitable charge specimen within the plug tips.
An inspection of the spark via an oscilloscope would indicate which of the above two is actually happening. Either way, the mod works a treat. Stock turbos may not feel the full benefit, but high-boosted engines will definitely feel happier (apart from the higher cylinder pressures, they also tend to run 'colder' plugs that are less efficient off-boost).
Then why did the manufacturer fit the resistor in the first place? Good question:
One reason is to contain the 'backfire' that occurs after the coil has discharged (a high-voltage spike is sent back into the coil). Having zero-resistance wires is regarded by most people as a 'good thing'. In fact it just shows that they don't understand how these ignition systems work. The manufacturer has added resistors on the path for reliability reasons, these cars are not meant to be rebuilt every 1000 miles!
Anothr reason is to reduce interference, which is why the recommended spark plugs also have inline resistors ("R" in the name). The stock ignition leads have carbon resistors in there, too (that's why they age and weaken the spark). Getting rid of all these resistors should theoretically make the car fizzle like a mobile phone mast - interfering with the ECU, the radio, the ABS - even the aeroplanes and satellites. In reality it runs just fine - all the people in the NOS forum run their cars like this and they've reported no dental fillings tuning to radio stations.
Please note that the long-term effects of such a modification are not known. There is now extra load on the coil and it might be forced to fail prematurely. Try it at your own risk - just like every other attempt to deviate from the manufacturer's design.
NASA knew of the beneficial effects (in terms of reliability of ignition points) of resistive leads back in 1945!
Has anyone on here done this mod yet to there cav/cally turbo or any car running a c20let?
Information taken off www.max-boost.co.uk, hope you dont mind johnny