CVZ 18 - speed and max RPM don?t seem to add up

[Mootspoints]

Continuing to get to know this boat.  Theoretically it should be running well.

Original 228 boat that the prior owner claims was replaced with a 350 ?short block? - I?ve just been hoping it?s not an automotive block, but not sure how to check.  Anyway?

Max speed I?ve obtained on the boat is 58mph and it?s topping out at 4K rpm, assuming the tach is right.  Speed was GPS.  The prop is an unmarked, unknown stainless 3 blade.  Hole shot is good and acceleration feels great, so I feel like it?s probably not overpropped, but I?m also not an expert at this point.  The owner gave me a 19P with the boat also, so I?m assuming the one on it is a 21P+, but no idea.

Thoughts on where I should be and how to get there? 

[Hyperacme]

Others have more info on the CVX18 / CVZ!8, which looks like same hull and about 100 lbs. difference in weight.
By your GPS speed .. you should have a 350 ci. SBC, and prop should be pretty close with the 21P you think you have.

1979 CVZ18 spec's
1984 CVX18 spec's

[Mootspoints]

Great info, thank you.  So I guess it?s in the ballpark.  For some reason I really thought this should be up at 5k+.

[Hyperacme]

21P prop at 58 MPH/GPS .. guessing your tach is off.
Check on back of tach for a "settings dial" , you could be at wrong setting for your motor.

[Mootspoints]

21P prop at 58 MPH/GPS .. guessing your tach is off.
Check on back of tach for a "settings dial" , you could be at wrong setting for your motor.

I?ll check that, thanks.  Never would have thought of that.

[Diamond Chad]

Sounds a lot like what I was getting when running a 23 pitch mirage on my cvx-18.  rpm below 4500, speed 58 gps.  Best speed was 61 with that prop in perfect conditions, and RPM was maybe 4600.