You always seem to catch on quicker than most Steve.

And hey Sam, You're right there with us bud.

And you would be correct . lol

Twin Turbos

Unless you can make same hp at same rpm the na motor will never compare to a sc motor. A local guy (todd kramer) had a 27 foot fountain, someone who supposedly worked for Sterling at somepoint built him a NA 540. Had a solid roller cam, dynosheet showed something like 745hp at 7300 or so from what I remember. He previuosly had a 502 and a 26 pitch prop, he bought a 30 pitch BEFORE ever running the motor, absolutely wouldnt pull it, wouldnt pull the 26 either. He ended up with a 23 pitch to break 78 mph but oil temp was sky high, cruise rpms sucked. My Baja at that time had a blown 502 that made about same hp but at much lower rpm, had much more useable midrange torque and beat the fountain every time we ran. Now sure, you could compare a blown 454 to a na 572 then the tq would be similar depending on boost, cyl heads etc, fwiw, Smitty

Well of course a 7300 rpm motor is going to suck in a boat.
Let's keep this conversation to real world experience that most people can afford, like 650hp for the NA and blower motor, and the blower motor has a top rpm of 5300 and the NA motor spins up a bit higher, say 5700 rpm. Now that's a real world comparison and let's say it is in a 32' deep vee.
I think that comparison is more useful to most people making engine build decisions here

Opinions on both have value.... However the question that should be asked is what engine package will twist the drive the fastest. Unless you have SSM. Even then 700CI NA is going to make a big torque number.

My point was based on a real experience, thats why I brought it up, Todd told his engine builder he wanted 750 hp and didnt want a blower, he got close to it but had no torque where it could move the boat so his 750 ish hp motor was about useless.
Now comparing blown motors to NA, you build a 500 cu inch 500 hp base engine, boost it 14.7 psi, the hp /tq increases 100% theoretically minus parasitic losses from generating the boost, 7.5 psi= 50% increase. Now of course base motor will make less hp NA if built blower specific. a good NA motor should last 400 hours if camming isnt stupid nutz, IN MY OPINION a blower motor RAN HARD should be rebuilt every 100 hours (thats what I do with mine) so a larger NA motor should be much less maintenance and less work. You can make up a thousand different scenarios, dice it up 50 ways from Sunday, everyones got a opinion , compare a low compression blown 502 to a big NA motor, argue till the cows come home, whatever.
IF a guy was starting from scratch, build biggest motor you can, even if boosted, run less boost and make good power, aftermarket blocks and cranks are all the same price regardless of stroke. Im running my current boat NA, probabaly will stay that way too, not sure how big I will make the engines when I do them, its a fast hull to start with so I dont really feel the need for 1000 hp motors

Did you ever meet Todd, he lives on 15 between richville and Vassar?

I'd say pretty darn close as well but it also depends on the hull it's going into. Like SB said, there's so many factors.

I also think the 565 would be much more affordable and you could get parts off the shelf to fix it if you ever had a problem. I would imagine the cost to build and rebuild the 700 would be much higher. You'd also be beholden to the manufacturer where the 565 most any reputable marine engine builder could work on it. I know that's not the original question but when I hear questions like this, these are the thoughts that immediately go through my mind. :-)

But you know what they say about opinions. :-)