I had to buy the 8hp because I couldn't pass up the deal. When using my 4hp It just seemed there was a lot of potential speed I was missing out on with this boat. The bottom of this boat is flat, just like a Jon (but in a different shape of course). I can't grasp as to why an 8hp wouldn't dramatically increase speed on a 110lbs boat properly weighted. The 5hp limit on this boat is because of the engine weight. Th Tohatsu 8hp engine is 57lbs, exactly what 5hp would weigh. The 4hp pushes me 8-10mph and I would expect the 8 to push me 15mph. I am really into the 8hp because it DO NOT have the internal fuel tank.
