</font><font color="blue" class="small">( Those engines that test "stronger" are then processed out the 35 HP door. The rest get sold as 30 hp jobs.)</font>
Greg, There has been many a discussion on differences of hp on a given engine model. I've seen this one posted in a few places, but from talking (email) with my china contact, do not have much faith that it is what actually happens. The engines are built at another factory and boxed and sent to the tractor factory. As far as I know, they are not put on any dyno and tested, prior to tractor assembly. Most engines are started after tractor assembly, but doubt that they are "power" tested at that point.
Out of the different theories I've heard, if there is an actual hp difference, it is most likely a different timing/injector pump adjustment difference. From my direct experience with a 254 and now owning a 284, I can not tell the slightest difference in real world performance. But, I also don't have any job that requires running the tractor at max rpm, where if there was a diffence, probably be where it would show up. The engine book that came with mine, shows multiple different hp/torque curves. I have heard that is the same with the 395, also. If I remember correctly, almost 40hp can be had from this engine. Now on the other hand, most buyers will think there is a major difference between tractor hp ratings, and not think about at what rpm range and if they can actually use that hp.