Merc set them up with low static compression which allows that much timing in boost. I run (525sc takeoffs) 28-30* with 9.5:1 static and it is safe but near the trouble area.

Merc set them up at 7.5 to 1 CR. They are very user friendly engines (that had a 90 day warranty) But not the ultimate blower motors, but very good conservative engines. I really like mine because it does not require a ton of maintenance and pushes my single engine, true 28 foot to "respectable" speeds.