964/993 twin distributor firing question

[911TT33]

Hi all,

When using a 964/993 dizzy on a 3.2 Carrera motor, do the two ignition coils need to be fired at exactly the same time / simultaneously, or are they slightly out of sync?

What about if a JB Racing twin dizzy with the 12 point cap is used? Coils fired simultaneously or not?

Much appreciated

[911TT33]

Bump

[Steve@Rennsport]

ALL twin-ignition 911 engines fire the plugs simultaneously.

[911TT33]

Originally Posted by Steve@Rennsport

ALL twin-ignition 911 engines fire the plugs simultaneously.

Thanks for clarifying Steve.

Reason I ask is because M&W ignitions has a Pro14b and a Pro14r unit which are both suitable for twin plugged Porsche engines. However, the Pro14r is designed for the 964/993 distributor but doesn't fire the coils at exactly the same time. The Pro14b fires both coils at exactly the same time.

I'm not sure if I'll use a 964 dizzy or 12 point single dizzy solution yet, but the 964 dizzy is a cheaper solution. Just wondering which M&W unit to go with

[304065]

Well, you go with the one that fires simultaneously.

The whole point of using twin plugs is to allow you to initate the combustion event at two points in the combustion chamber simultaneously. You've got a fairly large cylinder and a piston with a bump on the top that gets you in to the (nominal) 11.3:1 range (I know they measure less in reality). But the point is, in order to get the fire started early enough to have peak cylinder pressure in the right place in the cycle, and prevent detonation, you need simultaneous ignition of both plugs.

Starting one before the other would probably lead to detonation and engine destruction, much as if you lost one set of plugs.

On a rotary engine, different story.

[911TT33]

Thanks again for clarifying. I'll go back to M&W with this info. Cheers!