Ignition

Not too much to say here. There is no reason to use points in this day and age. John Eales recommends the standard Rover systems. Lots of people use Lumenition quite happily.

It is worth knowing how to tailor the advance curve to get the most out of your engine. The standard SD1 distributor has bob weights that are supposed to give 26 degrees of mechanical advance but they only give 22 degrees. The 3.5 litre engine needs 34 degrees of total timing at wide open throttle and this should be all in by 3000-3500rpm. The standard advance springs do not allow maximum advance until about 4000-5000rpm. You can replace the springs in the distributor with weaker ones (available from Real Steel among others) to improve this. Using this timing will result in about 12 degrees at idle which works very well with a fast road cam. It is enough to get the idle nice and smooth but not so much as to make starting difficult.

The bigger engines need less ignition timing, about 29 degrees for a 4.2 and 28 degrees for a 4.6. This causes a problem because the idle timing ends up at about 6 or 7 degrees which will cause a poor idle and the engine will sound really flat if the cam is longer duration than standard. It can also cause overheating problems in traffic. You can either modify the distributor bob weight stops to reduce the total timing or fit a different distributor. There is a Land Rover distributor that has bob weights that give 18 degrees of advance but I don't know what cars this was fitted to.

The vacuum advance should be retained for maximum economy but if this is not a concern then disconnecting it and locking the baseplate removes another thing that can go wrong.

There is a book available from SpeedPro called 'How to Build & Power Tune Distributor Type Ignition Systems' by Des Hammill. This explains everything you need to know about this subject. Alternatively most of the information is available at Dave Andrews' web site.

One final word. If you are not confident of what you are doing it is best to leave the distributor alone. Too much timing or an over-aggressive advance curve can destroy an engine through detonation!