I've not heard of much other then the new impellers which are just a cut back 6 7/8". I'm not sure if mercury has any other changes in mind. Been told they pushed pretty hard to get what they have out of them.
I've heard people talk about companies reflashing the ecm on them but I've not talked to anyone that's done it first hand. I figure if there was a gain to be had there everyone would be doing that.
Ok so I've been researching flashing a merc 40. From what I've learned the merc 40/28 is a detuned 60 head? If you flashed the stock 40/28 you end up with a true 60/40? Any thoughts??
Specs from the Mercury Four Stroke Jet web page.
https://www.mercurymarine.com/en/us/engines/outboard/jet/fourstroke-jet-outboards-25-80-hp/#specifications
Jet 25: Bore and stroke -2.40 x 2.36" Displacement - 32.1 CI
Jet 40: Bore and stroke - 2.56 x 2.95" Displacement - 60.8 CI
Flashing the 25 Jet is not going to give you a 40 Jet
That is about normal for that setup. You might get a little more with some work polishing up the impeller and pump housing. If it's a 40 jet it's a 60 powerhead 40hp at the pump not much that I know of you can do to actually gain more power out of the powerhead.
My last blazer 18/52 with mercury 60/40 four stroke would hit 33 consistently down stream by myself with fishing gear, full tank of gas. Would hit 30-31 upstream. It was a 2015 boat and motor. Sold that boat and have all 2017 stuff now. Same boat motor setup. Have not had it in the water yet. Will pleased if it will do the same.