Reduce the back pressure in the exhaust and more fule can passs through tobe ignited on the exhaust stroke.
I inadvertantly did this on a VW Beetle, decelerating into corners and a 1 meter flame and pop would keep following cars at a distance.
But that was a carburetor, i guess there would be a need to cause injector overfuelling nowadays, and the axhaust valves won't like it anyway.
It seemed like fun when I was 18, 40 years ago.