Got a run today on the ST 34 (just got the Davis head a few days ago) Its a ringed engine steel sleeve . It only saw 2 tanks of 5% nitro glow (not broken in and of course ring`hss s way to go to seat Davis suggests some more glow time with maybe a 10x6 snd running uo to 12K to get a complete ring seal. But had to try out the head 9500 on a 12X4 wood XOAR It will seat on diesel but will take hours, nice transition idle still high 3200 , gray smoke and rich want lots of oil going out exhaust at this point, when run in should pick up 500 rpm at least, engine machining is flawless and it is from China well worth $70 martin