Not sure you can rely on the afr, going from high power afr to 15 - 1 should have a big drop in HP

 

However the knock sum jumps to 5-6 cts fairly quickly though.

 

I wouldnt worry about it ruining your engine if thats all you did.

1.8 seconds at stoich would definately create lot's of heat near the ex valves if timing wasnt too advanced, but if thats all you did then it's nothing to loose sleep over. Ive done it before running methano; dry

 

Lol ya know I had to do it a couple times to confirm it wasn't an existing tune problem . wtf, it was a vac line on the manifold > fpr