Twin-Plug Ignition mapping?

[WydRyd]

Curious, how does a twin plug ignition map differ to a single plug map, in terms of degress of advance etc at idle/cruise/WOT? The reason I ask is because when I install the piggy-back ECU on my Motronics & the 964 dizzy, I'd like to setup a basic base ignition map to get me going so I can get the car to a dyno tuner for more precise mapping. Any input appreciated

[David]

My understanding is that you need less advance with twin plug since you'll have more complete combustion. Of course the dyno is really the place to set timing.

[WydRyd]

Sorry, yeh I meant LESS timing.

Any idea how much less timing compared to a single plug config?

[hobieboy]

To be 100% sure, you'll need a dyno.

For mine, my max timing (non-boost) is 29 deg (from memory) instead of ~32. On max boost, I retarded mine to 16 (from 18-19).

But then I haven't checked mine against a dyno neither, so YMMV.

[beepbeep]

Yeah. As mixture is ignited from two directions, it will combust quicker. This means that pressure will raise in more distinct manner and that you don't need as much advance in order to "wait for pressure to build up". This is also one of main reasons for twin plugs making more power: you can time the ignition so pressure spends more time pushing the piston down then before.

Correct readings should be found on dyno as it will differ from car to car. I suggest retarding it 5-6 degrees, then inching forward while measuring torque. When torque starts to drop off (or you expirience pre-ignition), it's time to back off.