I have a 7.4mpi in my 20' wellcraft Id like to get it up to 65mph on the gps right now it hits 59mph I have a mirage plus 21p prop the rpms are up to around 4300. can I get enough horsepower out of this motor to hit that by changing the prop and installing a thru hull exhaust?
dont know much about prop boats but as for the motor the exhaust will help a little.if it were a carb i,d recomend an intake also.you can try a differ throttle body,an msd type ignition.the easiest way would be internal mods starting with a little bigger cam.
I know I cant do to much due to the fact the internals are not as strong as the 454 mag, I just want to get another 5-7 mph and not wreck a year old boat
Your still running your exhaust tru the prop. Wow you can gain as much as 500 rpm by going to tru hull. I would suggest doing silent choice since you already have the down pipes. Don't chang the prop untill you get your rpm up to the WOT rating on the valve cover I think it should be 4800. I think your exhaust is holding you back.
I think the rev limiter id set for 4600 isnt it?
I would think the rev limiter would be set at or slightly above the WOT rating on the valve cover. Try the exhaust first before you do anything else. I gain 5 mph by opening my exhaust but I have a lot more HP than you. After you do the exhaust than get hold of a LAB finished 23 Mirage prop. Make sure its lab finished. Dont buy it see if you can try someones. If you cant get hold of a lab finished prop try a standard 23 mirage if this puts you up against your rev limiter than try a 25 pitch lab finished prop. Lab finishing will usually gain you about 200-300 RPM. What you are looking for is a prop that will just bump the rev limiter on a good day with a light load and 1/2 tank of fuel.
[This message has been edited by Tinkerboater (edited January 06, 2002).]
I really dont want to go to a lap finish due to the fact lake erie will low again this year and its about a mile from the dock to the lake. if we get alot of snow I may change my mind and get a spare prop thats been lapped
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