I have a thread on same subject right here in the Pattern forum. We have tried only the SAP180HP. Turns pattern sized props well, as well as (better than actually) the OS140RX/160FX and webra 145. A few people have used MVVS26cc, others ZDZ40 cc. The ZDZ40cc is pretty heavy for pattern but is also rear exhaust and rear intake, like the SAP is. I have not heard yet of anyone using the DL30cc in pattern, but I'd expect that to be inevitable now that they moved the carb to the rear.

The new YDAero 38cc looks promising if they can deliver the weight and mid range torque they keep talking about. I hope it isn't all just hype. Price is on par with the others.

Mintor also made a small gassie, 37 cc as I recall, at a really good weight. Pricey compared to the small gassies but much less than a YS170!!
BUT, Carb location on that engine killed it for pattern work