Should be pretty accurate. The PCM knows how much fuel it is feeding the engine.

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I know most NA OBs are doing a lean burn at part throttle based on a wideband o2 feedback.

I doubt the 520 does this.

Supercharged Merc OBs are obviously also thirstier than NA OBs.

I will say that weight difference is big. My fuel economy drops a lot with a load of people and fuel.

The thing going unmentioned is that the OBs allow for a significantly longer warranty period.

Between my MTI/450 boat and my DCB/450 boat, and now my 300V8 Airship RIB, I have about 375 hrs with no real issue. One O2 sensor on the MTI(fixed in 20 mins) and one belt shred on the DCB, fixed in 30 mins.

Also, if you lose a prop shaft on an OB (with a merc prop) they replace the prop as well. And I have two sets of cleavers always within grabbing distance. Just in case.

And two 450/500r motors on a most hulls will easily outrun a 520/540 due efficiency or props and higher rpm.

450's will beat up the 520's in any performance cat... the 500's will undoubtably do the same. The only downfall to the 450's is the prop-shaft issues, now the major issue with the 500's is insurance. Wozencraft told me that you can get insurance on a V bottom with 500's but nobody is writing cats with them. They are hoping this winter or early spring... that sounds expensive. I'm building a new boat and decided on 450's because of this issue, luckily I found a new set with full warranties for less than most used ones with high hrs and would have to be repainted to match your boat. I might not be the coolest kid on the block but I can always re-power in a couple of years.

Does anyone know yet if the 500's lowers can be put on the 450's?

It would be a bummer if it didn't.

Just guessing: since the key problem has been broken prop shafts, there should not be a reason to spend money redesigning the mounting pattern to the mid section or the drive shaft.

A new lower that doesn't fit would be the kind of thing that OMC would have done.

Any idea of what share of 450Rs use FloTorq props? (What props are all those center consoles running in the first place?) Are there FloTorq hubs for the 500R prop shaft, or is the diameter too large?

I believe the down shaft is larger as well as the prop shaft. So not likely to fit.

Hey Greg...Correct. I was told shaft and many parts are larger in diameter and beefed up. When are you putting a pair on the DCB

Bummer.