There more to it than that , Pistons are different along with ignition parts and Flywheel and even intake system. I wouldn't recommend turning a Promax over 6500 for reliability ressons , like I said its a production motor with a few goodies.

What limits the promax...I got no problem with mixing oil and removing a rev limiter...are you saying the bearings in the promax won't hold up above 6500??

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Thte 260 and Bridge Port are racing motors and have better crankshaft bearings for higher RPMs, The 225 Promax is a Modified production motor came with oil injection and can not turn higher rpms max on Promax if I'm right is 6500 but is a strong little motor. Hope this helps

Im currently rebuilding a 79 vector. Core, floor, transom, everything. I'm looking for it to be 100+mph boat. I'll be shaving weight everywhere I can but Im not sure what motor i want/need. Thinking about a 2.4 bridgeport, promax 225, or 2.5 260, possibly others. I mean I know the 260 will get to 100 without being too radical but im not sure about the other 2. Granted I'm aware all of them need a rebuild every 100 hrs or so. You guys are the experts on here, what kind of speeds do you think each motor could expect with the right setup. Ballparking the number of course. Advice on the motors in general? Thanks for your help!!