I have just purchased a 2007 Checkmate 230 ZT with a 500 HP merc racing engine and a HP Imco 1 in shortened lower unit with a 30 in. pitch prop. Can't get past 4,200 RPM and 60 MPH. Need help. Was told that the boat would 100 MPH which I doubted but I thought it should do maybe 75 or so.

Absolutely one of the silliest first posts ever! Seriously Dude?

Thanks for the input. Your nose must be stuck up in the clouds.

OK I'll bite...Did you go for a test drive with your new boat? Who did you buy it from? Please post some pics so we can see your new beast. I would get in touch with the previous owner/person who sold you the boat and verify the advertised speed. 23foot checkmate boats with 500hp don't go 100mph.

It'll never go even near 100 with the 500, but 30 pitch is too much, try stepping the prop back to at least a 26 and you should pick up the rpm and some speed.

23 zt? or 24?

first off im 99% sure the short drive is going to kill you on that boat.
from what i have seen the newer zt hull 24 or 26 do not do well with 3 blade props or short drives.
i would say go to a stock lower and a 26p prob and try again.
as for 100, no way. 75 maybe

Is this the boat you bought?

http://boats.smartcarguide.com/listing/30646928/

Noyzee, I tried a four blade 26P prop and picked up 1,000 RPM and 11 MPH top end she'll now do 71.1 on GPS at 5,200 RPM

GeeterB I Tried a 4 blade 26P prop over the 30P prop and picked up 1,000 RPM and 11 MPH om the top end. She'll now do 71.1 on GPS at 5,200 RPM

rchevelle71 I tried what what you suggested and what a difference. A 1,000 RPM gain and 11 MPH increase on top end. 71.1 0n GPS at 5,200 RPM