I'll make a nonsensical suggestion when choosing a motor. A lot is said about it takes x amount of hp to pump x amount of oil. That is true, but my personal opinion is to go bigger on the hp than the suggested hpxflowxpsi numbers. My reasoning is just my opinion, so take it for what it is, an opinion. My reason is simple, a motor under heavy load will Burn more gas and run at higher temps than a engine at lesser load. Splitters that have the minimum size engine they can get by with will always loadup splitting the hard stuff. This loading up will reduce oil flow because the rpms of the motor will drop. With extra hp, the engine will not reduce rpms, or not so you can tell it, and burn less fuel because of the increased cyl speed. The bigger engine might burn more fuel per hr, but you will get more work done in that hour. I am not saying to put a 671detroit on a 11gpm pump setup, but if the minimum spec is 5hp, there is something to gain from going to a 6hp or even a 8hp engine. I have a 27hp kohler pulling a 28gpm 2stage pump. This combo is over kill, but I had the engine so I didn't have to look for one. The motor never boggs, even when I stall the cyl. It will work 5 men in the ground keeping the 5in cyl fed. If I ever have to replace the engine, I would not go with the 27hp, but I would want larger than the 16hp recommended size for my pump.