Jaguar Repair: Series III ignition advance, detonation point, bosch distributor

Question
Hi,
I have an e type fitted with a 1987 series III 4.2 XJ6 engine. The engine is fitted with triple SU's and a standard bosch distributor with points. I have recently purchased a 123ignition ( electronic distributor) and I am having trouble selecting the correct advanve curve for my engine. The information with the new distributor says "if you know the maximum advance for your engine e.g. 30degrees select say C on the distributor and if this works gradually increase this to D and E until the engine pinks and then go one setting back. The trouble is that I thought the max advance was 36degrees at 4500rev but I am not sure what to select. It idles well at this setting but does not run well when revs increased. The settings listed on the info sheet are 10before TDC, __degrees at 2500 and __degrees at 4500. I would be grateful if you would know the correct curve to start with?
Thanks
John

Answer
Hi John,
They are telling you how to set it. Max performance on any engine is to set the timing advanced to just before detonation (pinging).
Any time you alter an engine in any way you change what advance curve is the max performance. Many things effect that, so all cars set the timing and advance curve at a compromise. (Except some of the new cars that have a knock sensor system that keeps the timing at close to that destructive detonation point.)
Their instructions are telling you to set timing at their letter "C,D&E" which I guess changes the curve electrically. A change in advance curve should not alter total advance so you should set total advance first for the specs of the engine. If you have put the three SU carbs on the Ser. III engine you are starting from scratch anyway on a curve. But 36 deg total advance should be ok, then just play with their changes in curve. The standard method to look for the Ping is to get the engine hot and let it idle down and quickly open the throttle and listen for the tell-tail rattle. Then a final test is to have someone in the car put it in gear and hold the brake hard and give it a good amount of throttle like you were doing a auto transmission stall test. Don't keep doing it or you will be looking for a transmission. Detonation usually happens under acceleration or heavy loads like going up hill. High speed detonation is very difficult to hear so most racers either use a dyno to find where it is or use of knock sensor systems like the one MSD sells.
Good luck, let me know how it turns out.
Howard