Negative ignition timing vs valve exotherm temperature

Question

I am setting up antilag and I have no ability to do an ignition cut. So to emulate an ignition cut I am setting ignition timing extremely negative to induce a misfire.

Where would the valve exotherm temperature peak? 0, -45, -90 degrees timing?

I'm imagining if you set it too late and the exhaust valve is closing and you ignite the fuel, it will cause a very hot edge on the valve. But if you ignite it even later most of the fuel should be out of the cylinder already, so you will only get a very small amount burning as it passes the valve edge. This will obviously depend on valve/cam timing, but I'm after a general answer.

Thoughts? Edit: By -90 degrees timing, I am referring to 90 degrees AFTER TDC. Eg on the down stroke of the combustion cycle.

Answer 1

If you want to simulate ignition cut, you could run at + (or -) 180 (plus or minus your normal advance) so you'd fire the spark when the cylinder was at the top of it's exhaust stroke before the inlet valve re-opens (this is where the Alfa twin-spark competition cars run their secondary spark as any fuel remnants will be burned here). Of course that's assuming you aren't running a wasted spark setup because if you are, you're already effectively firing the spark at this time.

However, in order to implement anti-lag, surely all you want to do is fire your spark late (i.e. when the exhaust valve is open to ignite fuel in the exhaust system). I don't know what type of ignition system you're running but surely a relay to make the LT side live could be used to cut the ignition by simply switching off the power to the relay when you don't want the plugs to fire?

Very high temperatures are a byproduct of this type of anti-lag implementation I'm afraid. Use sodium filled exhaust valves, ceramic coat as much as you can and make sure your system suspends anti-lag when the coolant begins to boil.