Currently I have a 90hp yamaha on my 5.5 surtees and am looking at the options of repowering.

Do it NUMBA 2 - F100

i've got the Suzuki DF 90h on my 5.5 hardtop and it goes just fine...in fact better than fine...it's as cheap as chips to run...and quiet as a quiet thing. I cruise at 18.5 - 22 knots. Can do 30+ if I really put the hammer down. I've considered powering it up from time to time, but it aint worth it to get another 2 or 3 knots of speed. If ya skiing or pushing a lot of weight then things may be different. I normally fish with me + 1 other, and often also have either a 115 or a 180L bin full of ice/fish so i guess thats the equivalent of a few extra fellas. I have filled both bins before and had 2 people on board and it was slow going coming back...but we were so stoked that didnt matter :-) 

Catchelot wrote: I wonder how a 90HP Etec or Optimax would go, lighter faster and damn great on gas too.   But if you are gonna upgrade I'd go 115HP.

I have a 90hp Etec,did the hole shot race thing two up with a mate with a F115 - He did catch up but was left on the start line for a wee while...top end he could get another 5 knots.Fuel econmoy was worse than mine.

not sure that you will notice a lot of difference if you replace a 90hp motor with a 90hp motor
and as falco points out going from a 90 2stroke to a 100 4stroke will be a backwards step.
Agree with catchelot re the 115 - the best option for these boats seems to be the 2stroke 115 V4 yamaha - its grunty and lightweight - 2 things that these hulls need

captain.Gav. wrote: I re-powered my 5.5 from a 90 two stroke to an 115 opti and the difference was great for cruise speed and carrying extra people and gear. However, the oil costs were huge for the spec oil and i believe the etec oil is even dearer.        AND the opti was a crap motor and well earned its nickname of "OPTI-BOMBS"     I would go 4-stroke 100 hp or higher. Better for towing lures around, less oil costs, less smoke, quieter, more reliable!  Unless doing lots of skiing then fast holeshot is not that important but if a modern 4-stroke is proped right then they holeshot pretty good aswell.

The Optimax nickname really only came about because of the early 3.0ltr 200-225HP, they where withdrawn from sale at one point to do updates to the system, some of the failures where due to incorrect servicing of the engines and also incorrect prop fitted, from the point that the newer versions of the Optimax where launched there are not that many issues compared to other DI two strokes
Certain items on the engine need special attention, but they will do over 2000hrs in the domestic market with the correct servicing.