I had a 225SS on my XB03 and LOVED it once we got the slippage issue on holeshot cured, had to have dual PVS holes on each blade because the majority of the exhaust in a 15" mid goes out over the cav plate instead of thru the hub. And of course the offshore trim is bombproof but extremely slow unless you do either 24v or put a Alpha pump on it. (Which would be my recommendation for a lake/fishin boat) And of course THE best thing about a 15" mid is the rock and roll sound and kickazz looks of them.
But on my XB21, NO WAY JOSE!!! The boat is so much bigger it would look queer as a $3 bill to begin with IMHO. The hull is alot deeper back there so a SS motor would look like a 9.9 kicker and would get dunked everytime you came off plane. A 21 is a fully grown boat, it needs a fully grown motor.
Think about this... My 2+2 weighs nearly 1500#s. An XB02 is under 1000 so right there the 2+2 is appx 50% heavier than the XB02!!! :surprised
Don't get me wrong, I'd LOVE to play with a big block XS motor on a XB02-03 with a custom/trick 15" mid and reduced setback. On those rigs I think you could pull it off. But like I said, the 21 is so much bigger I just think you'd be alot happier and the whole thing would look and perform better with a 20" mid. Because of what I said about the exhaust, the SS motors just don't have the power/slippage when you stomp it from a dead start that the 20" motors do. Now obviously with any of the 20ftrs you can play with skidplaners, balls in the jackplate, over hub props and alot less total weight so the 15" motors can be made to rip out of the hole on the smaller boats. But I just don't believe you are going to setup a 15"er on a 21 and ever have it get quickly out of the hole and haul the loads that most of us do with the big boats. Ask Neal (GotMyAlly) Edwards, he owned his XB21 ProSport for a year with a great 225X on it (was previously on his XB03). And back in January we put a 250XS on his XB21. I'm sure he'll comment but you'd probably have to pull a gun on him and threaten family before he'd let you replace his big XS with another smallblock motor on his yellow barge!
And I won't even go into the fuel/oil savings between the XS motors and regular carb/efi engines, :beer:
RA