Struggling with speed on my '97 253 Convincor

[H20 Guy]

I bought a '97 253 Convincor with a 454 mag, 365 hp, and a 23p Mirage prop. Max RPM is 5100 but only hits 54-55 mph and cruising causes cavitation. Could I have the wrong prop or a spun hub?

 

[onigiri]

Yea it's possible you got a spun hub or the wrong prop for your setup. Max RPM but only reaching 54–55mph? It surely suggests the prop might not be hooking up properly. You should go ahaed and check the hub for slippage and consider testing a different prop to compare performance.

 

[H20 Guy]

Thanks, onigiri. I'll inspect the hub for any signs of spinning or damage. I am also gonna try swapping to a slightly different pitch prop if I can find one, see if that helps with cavitation and top speed.

 

[T0NYT0DD]

I bought a '97 253 Convincor with a 454 mag, 365 hp, and a 23p Mirage prop. Max RPM is 5100 but only hits 54-55 mph and cruising causes cavitation. Could I have the wrong prop or a spun hub?

Agree with @onigiri and I'm glad you got around to checking the hub and testing a diff prop. Did it solve your problem though? The 454 should push better than 50s.

 

[Ch3ckmateSkipp3r]

Sounds like you're doing the right things by checking the hub and trying a different prop. If you're dealing with cavitation and a lower top speed than you'd expect it usually means the hub might be slipping, or the prop isn't the right fit.Fingers crossed that swapping the prop does the trick! I'm really curious to see how it turns out

 

[H20 Guy]

Agree with @onigiri and I'm glad you got around to checking the hub and testing a diff prop. Did it solve your problem though? The 454 should push better than 50s.

Not yet, I just got the replacement prop lined up and plan to test it this weekend, I am hoping it hooks up better and gets me closer to where the 454 should be running

 

[WaterGambit]

I just want to add that if the hub is good, your 23p Mirage might just be too much prop for that setup, especially if you're loaded down.
You might consider dropping to a 21p to see if that gets your RPMs up closer to the optimal range for the 454 Mag and helps with the cavitation.
It's often a bit of trial and error to find the sweet spot!

 

[vanilbean50]

Yea it's possible you got a spun hub or the wrong prop for your setup. Max RPM but only reaching 54–55mph? It surely suggests the prop might not be hooking up properly. You should go ahaed and check the hub for slippage and consider testing a different prop to compare performance.

that RPM and speed combo, plus the cavitation, really screams propeller issue. either a spun hub or just the wrong pitch/style for that hull and engine

 

[VinoStefano]

I just want to add that if the hub is good, your 23p Mirage might just be too much prop for that setup, especially if you're loaded down.
You might consider dropping to a 21p to see if that gets your RPMs up closer to the optimal range for the 454 Mag and helps with the cavitation.
It's often a bit of trial and error to find the sweet spot!

I'm with you on this one, if the hub's good, that 23p prop might just be too big, especially when you're loaded. It's definitely trial and error, and things like load and conditions play a role. Watching your tach and how the boat feels is the best way to find the right prop..

 

[SixFourtySeven8]

I just want to add that if the hub is good, your 23p Mirage might just be too much prop for that setup, especially if you're loaded down.
You might consider dropping to a 21p to see if that gets your RPMs up closer to the optimal range for the 454 Mag and helps with the cavitation.
It's often a bit of trial and error to find the sweet spot!

Thanks for this! But how do I know if my RPMs are in the right range for the 454 Mag? I've heard 4600–5000 RPM is ideal at wide open throttle, is that accurate?