MG Car Repair: Ignition timing, detonation point, vacuum advance

Question
My competition MGB requires a very high 18 degree BTDC as it has a highly modified cylinder head with high compression. The engine idles at 1200 rpm. Getting the starter to turn the engine over can be a problem. Can you offer a solution, please. How do I check the maximum advance.

Answer
Hi Era,
If you have a vacuum and a centrifugal advance, all you need to do is to remove the vacuum and plug it and run the RPM up high with a timing light and check the timing. Then let it idle and note the timing with the vacuum advance connected and use a vacuum pump to pump up about 5 in. hg. and see how much the timing advanced. Take that figure and add it to the other timing you came up with. (most engines will still produce 5 in vacuum at full throttle and full load)

The most horse power occurs just before detonation but high RPM detonation is hard to hear. To get the max advance possible on any engine, it requires a Dyno. But MSD makes a LED display of knock so that is another method to advance to just below that destructive point of detonation. Another method is to install one of the ignition systems that has the knock sensor system in it. These systems can advance the timing to just under detonation point and even do it for each cylinder individually. Very expensive though. Electromotive and MSD each have a system that does that.

Starting a modified engine can be a problem and may require a method to retard the timing just to start and advance it after it is running. The Electromotive direct ignition system has an optional manual control of ignition timing so you can just slide a control to retard the timing.

The standard Lucas distributor mounting plate has two bolts in slotted holes so It is possible to set your correct timing with the slots in the most advanced position and keep the pinch bolt tight on the distributor and just loosen the two mounting bolts and rotate the distributor to a retarded position and after it is started just rotate it to the advanced stop point and snug down the two bolts. This would be too much trouble if it is used for street use but ok if it is a race car.

If it is a street car, you might look at a diesel battery or one of the aftermarket gear reduction starters.
Howard