I just picked up 1979 233 with twin 5.7 litre mercruiser tempest engines. Each motor is rated at 300 HP and are epuiped with 21p props. Any. Ideas on a top speed? the last owner ran 69.8 on GPS, I think it could do more. Hoping for mid 70's.

If the 21's are the best prop for the boat then I am going to say about 60 mph maybe a little more.

I thinks its higher then mid 60's. Last owner ran 69 on gps. Any more guesses?

Uhh....69.8?

What are you going to do different to get more mph? And with 21p props, you have to be turning more than 5k rpm.

a friend has a 255,when it had the twin 260's it would run 55 mph with 21 lazer props

I don't know what to tell ya other then the guy was full of ****. I really don't want to bum ya out on your new purchase but my boat spinning 23 props at 5400 rpm is going just at 69. When I put 26's on it I got the same speed but could only turn a little over 4800 rpm. So with 21's you would need to be turning about 6000 plus RPM's. I don't think you can spin those motors up that fast.

Hate to also ruin your day, but you'd have to spin those motors at 6000RPM with 14% prop slip to hit 69MPH. Knowing what I know about Formula hulls, that slip is probably not going to happen nor is spinning the motors that hard. I'm guessing that 55-60MPH is what you'll see.

theirs a guy that runs his 233? where i boat,he took out the twin 350's and restrung the boat..He put a 700 hp 540 in it with a single bravo one and a imco -2 shorty drive.. my donzi will run a bit over 70 and he runs rite past me..he claims it will do 80..

well I'm not surprised the guy lied to me, he was a dipsh*t anyways. Sucks to hear all that negative jazz but I guess once the boat hits the water I"ll find out for sure. Currently replacing stringers and everything else. what do you think the weight on this thing is? It has twin 350's and a 55 gal fuel tank. I'm guessing about 5500-6000 with full fuel and no passengers.

If it's all apart now, how hard is it to throw better intakes and cams in the engines? More power/torque and you could go to higher pitch props. Done.