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I bought a used DF115 lower unit for my 2012 DF140 on eBay, and it worked as it should, except for one thing: I thought the ratio would be the same, but it isn't. Before the old lower unit went the way of the dodo the Solas BPP-3413-138-19 13 3/4x19 four blade prop gave me around 30 knots with 6000 RPMs on WOT. The boat is an aluminum fishing boat that weighs around 3000 lbs with the engine. When I finally got the chance to test today I topped out at around 27 knots on 6500 and didn't dare to go furthere, there was a little bitt left on the gas handle. And 2/3 speed gave me around 17 knots, it used to be 20-21. So obviously the ratio isn't the same and I'll probably use more fuel for the same trips. Fuel here in Norway cost around 10 dollars per gallon, if I have converted it correctly, so using unecesasry amounts to get from A to B will be expensive quite soon. How much should I change the pitch to get to some kind of sweet spot?