[What'saCobra?]

MSD 6AL is a great piece. The reason why it 'wakes up' engines under 3000 rpm is because it fires the plug multiple times under that rpm. That is why it is called a Multiple Spark Discharge (MSD) system.

Above 3000 rpm there isn't enough time to fire more than once, sort of, so only one big spark is fired off.

Several precautions are suggested, however. Be careful not to attach your nice new tach to either of the coil terminals when the new 6AL output is attached to them, as will be the case. ONLY attach the tach to the 6AL tach output, a dedicated blade plug on the end of the 6AL. Otherwise, say perhaps goodbye to your tach, particularly if it is an older electric tach and a real Cobra type and size. (Don't ask me how i know!)

Also, be prepared to use an isolater/amplifier tach driver in the system if you use an MSD magnetic trigger (for instance, using the billet MSD distributor, a fine piece also), rather than the points as the imput to the 6AL, (which MSD is the only way to go for great maintainability and input switch control.) Even using the 6AL's tach output, some tachs will show nothing, without the $50 adapter for your tach. SW tachs are OK, usually, but some AutoMeters will not be OK and will show nothing w/o the adapter.

Download the MSD and tach diagrams and determine if the tach adapter is necessary.

But, don't let this little tach technical thingy dissuade you. The MSD works absolutely great on an engine that is struggling with a DuraSpark or regular points system...

And you thought you had a carb problem!

By the way, when it misfires at the chipped rev limit, it rotates the cylinder chosen for the miss from the entire eight, rather than just one, which reduces plug fouling and reduces backfires.