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I don't get it... (archive)

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Posted by Ben '74 tii on December 24, 1999 at 15:53:49:

In Reply to: Re: twin spark ??????????!!!!!!!!!!!!!!!! posted by XBeteNoirX on December 23, 1999 at 23:35:19:

: Multiple spark plugs are used to permit the use of lower octane fuel in a combustion chamber which is poorly designed. Usually it is considered a temporary fix until a new cylinder head can be designed, cast and tooled (and bugeted).

I don't get it Alfa Romeo just came out with a whole new series of high-output motors that use two spark plugs. Mercedes-Benz just came out with a whole series of twin spark motors, too. These were blank-sheet-of-paper designs, not temporary fixes.

: Multiple spark ignitions are a complete waste of money since they only provide multiple sparks at low engine spreeds. Above about 2000 rpm, the multiple sparks blend together to form a single spark.

Right, both plugs spark at the same time, but it was my understanding that by initiating the spark at two spots in the combustion chamber ensures that the mixture burns more completely.

'74 tii

: What is needed is an ignition system that doesn't misfire at higher (above 5000 rpm) engine speeds and provides enough kilovolts to fire larger (.035") spark plug gaps.

: Once the plug fires and the mixture ignites the spark plug serves no further purpose. Provided that the mixture ratio was correct and fuel completely evaporated at the time of ingition. In the real world, this often does not happen. So...

: ..what we really need is an ignition system that provides substantial spark duration (25-30 deg) at higher rpm. It doesn't matter if it is triggered by breaker points, electronic, magnetic, crankfire or matchsticks. What does matter is the voltage output of the coil. If you find a really good coil, most ignition problems magically disappear.

: MSD type ignitions use staggered capacitive discharge systems because the spark duration of a CDI system is so very short. The best performance is obtained using an induction coil or multiple coils (maybe one per cylinder?). Bosch doesn't even make CDI systems anymore since they are obsolete. Check out BMW multiple coil ignition systems and figure out how to retrofit one of those.

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