RinconVTR, I've had the same question/idea for quite some time now also. My TYM T273 has the same engine as the T233 and T293 so I often wondered just "how" does that happen? 23hp from the 233, 27hp from the 273 and 29hp from the 293; all from the exact same engine! Go figure! But, to start blindly messing with fuel pumps, pressures, etc., etc., is very likely to swiftly cause $$ problems! Since I don't have any problem with my machine the way it is, why go messing around is my current thought. However, an honest answer is always appreciated. So I wonder how is this done. Greg
For comparison sake, my Yamaha 4 stroke gas 225 HP outboard comes in 225-300HP with 225 and 250HP also available, in the EXACT same displacement/weight category, IIRC. I wondered how that was possible when I bought my 225HP engine. If I'm not mistaken it is done via fuel injection tweaking in the computer; and believe me a six cylinder Yami 4 stroke is a complicated engine by any comparison to a diesel tractor engine. No slam intended here, just saying if it can be done on the outboard with all it's sensors, etc. up or down tuning a diesel should be a relative cakewalk for most manufacturers.
FWIW, here is a link to a description of how the engines make the various HP upticks through precise fuel metering, like what Fred alluded to in one of his posts.
"Introducing the next generation of Yamaha Offshore outboards.
Yamaha proudly announces the next generation of V6 Offshore four-stroke outboards, the F300, F250 and F225.
Highly evolved and perfectly adapted to the offshore marine environment. With their big bore 4.2 litre displacement, these engines are exceptionally powerful. Their big capacity has been matched with Yamaha’s Variable Camshaft Timing system that dramatically increases power and throttle response at low and mid range RPM. This allows Yamaha’s new 4.2 litre big-bore V6 Offshore Outboards to deliver awesome “out of the hole” performance and mid-range acceleration you have to feel to believe.
Class leading 4.2L capacity has been achieved by using a highly-advanced thermally-applied plasma fusion process on the cylinder walls. This is a feature, more commonly found on high performance sports cars, that makes Yamaha’s new V6 Offshore outboards like no other outboard motor ever made.
They have no conventional steel cylinder sleeves, yet the cylinder walls are 60% harder than steel. Sleeveless cylinders mean larger cylinder bores for increased displacement, resulting in more power and torque. This is all achieved without increasing the overall size of the engine.
It also results in
better cooling properties and dramatically lighter weight. Amazing weight savings have been achieved on Yamaha’s new Offshore V6 range for maximum performance without sacrificing durability. In fact these motors are the lightest in their class by quite a margin.
All air entering the engine block of each Yamaha V6 Offshore outboard is routed through a single 75mm electronically-controlled throttle valve. Working in concert with the Precision Multi-Point Fuel Injection System, together they
help ensure the precise amount of air and fuel necessary for optimum power and fuel efficiency.
Yamaha V6 Offshore outboards are compatible with Yamaha’s new electronic rigging system. Featuring a new 5” high-contrast, multi-engine, LCD display, new Electronic Controls, and new key switches and start/stop panels, this system offers more convenience, flexibility, and information than ever before."
