Similar results to water injection? What temperature steam? Increased advance would happen with knock sensors.
Had a guy who tried something similar, he encased the exhaust manifold on a Sigma and ran the carby very lean, pumped water on to the manifold and fed the steam into the intake. Claimed very good economy figures and I would believe him as he was quite methodical. Sadly being a Sigma the head cracked. He gave up as he was in his late 70's.

