I know some ST46s had it and some Jett engines have it (including ROJetts? I don't know...).
Is sub piston induction really a killer on muffled stunt engines?
From what I read all the downsides don't really matter to us anyway; throttle control, peak power etc...
Reason I ask is that I have an engine or two that could benefit from having the liner dropped and the ports tweaked. Problem on both is that the piston is already trying to lift its skirt over the bottom of the exhaust port, so any liner drop is going to result in SPI. A new liner is only the cost of a few good glowplugs, so I might do some experimenting for the hell of it, but I could use some opinions from people who know in the meantime!