lOOking in se4arch on the knet , The 39 looks like maybe a OS Clone ,
Theres three ' .40 ' TS on ebay , look lihe SF OS clones .
Looking at this , Id think theyve ' pipe timed ' or raised the cylinder timing , like the ASP are ( all ) .
https://sceptreflight.com/Model%20Engine%20Tests/Tiger%20Shark%2040A.htmlId think ' build ' quality would match this .
If its NOT a plug in head , it mightbe something like these .
https://sceptreflight.com/Model%20Engine%20Tests/OS%20MAX%2032%20SX-H.htmlBUT Id think the Ex Timing about 10 degrees more than OS , so likely ' blowdown ' excessive for a 4 - 2 run .
90s / late 90s there were fancy muffler tuning wave length stuff going on , so likely a high rpm engine .
You never know untill you try it . That TS 40 has a broad flat tourque curve . Tho 90s they were getting adequate build quality & suchlike to emulate expensive stuff , like ROSSI , mass production .
As In earlier , a 18.000 rpm peak cheap motor wouldnt hack it reliably . Theres T S referances via search on RC forums . was a 61 too looked like the OS SF . Helicopter Engines & suchlike , many then .
every man & his dog were at it , and were a profusion marked here in Aus . And the ' sticker ' 40 / 46 SF OS clones , like LEO etc . All they did was fit a differant sticker on the bypass , for the differant ' importer '