Traction control_ignition retard

[Holmz]

I can see no explanation of how the combustion can get through an open intake valve, except from the exhaust or from within the cylinder itself.
An exhaust flame induced intake combustion may be possible through the overlapped, and open, valves.
The other option is a spark induced combustion.
If it is sparks, then they are either firing at an incorrect timing point coming out of ignition cut, or it is a wasted spark which always fires close to the valve overlap.

The manifold being wet, has about the same F:A mixture is in there with the cylinders firing.
So it will be the pretty close to the same "wetness" as when the sparks are flying as when the ignition is cut.
There may be better scavenging with a hot exhaust exiting out the tail pipes, leading to better airflow through the engine, so it could be a bit "wetter".

If there is better scavenging with a hot exhaust exiting out the tail pipes, that would lead to a lower cylinder pressure. So a higher cylinder pressure should/could exist in the cylinder at valve-overlap when the ignition is cut due to the loss of scavenging.

When in normal operation the mixture in the cylinder at overlap would be wholly exhaust for the combustion products, until the intake either gets dragged in by the exhaust scavenging effect, or forced in under pressure a while into the overlap period... Or a combination of the scavenging and boost pressure..

Between the higher pressure and the higher percentage of "a good F:A" during overlap with the ignition cut, it should be easier to light up the cylinder when the intake valve is open.

So if it was wasted spark then there should be a higher likelihood of combustion when coming out of spark cut.
If it is not wasted spark, or incorrect sparking timing , then it would have to be exhaust induced.

If I understand engine operation theory correctly then using the TC scheme of "ignition retardation" would have better scavenging and less F:A at valve-overlap and probably less chance for the flame to run in the wrong direction.
On a turbo car it also could aid in maintaining, or even building, the boost.

[MarkMc]

Basically back then the car was on Gas not petrol the ECU was just running the ignition. We were messing around with TC but wanted to keep away from Cut as this type of explosion was expected. We did most of the TC with Retard but had to have some Cut come in as a safety feature........one that blew the manifold up apparently..

[Allan L]

the other issue was with no LPG (fuel) cut ign retard caused the car to go into "antilag" (turbo 3ltr ~340rwkw) and actually made wheel-spin worse... I think IJ has a log of the rear's going up in smoke at 160kph and this was the motivation for drive by wire traction control...

[MarkMc]

Didn't make the wheel spin worse, the TC did actually work but the anti-lag stagement was correct, we made a lot of boost when the TC was on....hence the need for some cut.......and then unfortunately some rather large bangs.

Luckily Ian is a pretty handy welder.

[Scott@FP]

I had a customer car once (4 cyl. waste spark) that had an improperly wired CDi unit in it, fired ALL 4 plugs every 180 crank degrees, plus current ign adv value. Had nitrous too. No booms. Go figure.

How did it NOT ignite the intake stroke BBDC event? No clue.

VERIFIED all 4 were firing at once every 180 crank.

[Mazi]

Combined DBW and up to 30deg retard TC on 620HP Porsche 996 Turbo with plastic inlet manifold without any trouble.

[MarkMc]

It's something to do with a fumagated gas system, not sure what but a pertol engine can have loads of cut without blowing the intake off it.