more horsepower

[kdrelich]

I have a 1991 Johnson 250 V8 that I'm planning to rebuild this winter and was wondering what it would take to convert it to a 300hp model

 

[OBJ]

Re: more horsepower

Hi rudedawg, welcome to the iboats forums.<br /><br />Don't have a manual to give me the specs on the blocks, but I can tell you that new carbs with throats for 300hp would be needed. This is about $438 per carb assembly and 4 are needed. Big chunk of change their just for carbs.<br /><br />Think if it were me, I'd stay with the 250hp and be happy. Get a OEM service manual to guide you through the rebuild and do the best job you can. By the by....is there a reason for rebuilding the 250?

 

[kdrelich]

Re: more horsepower

OBJ thanks for the info,I wanted to freshen things up a bit, i've almost 1000hrs on it and I fish offshore of NJ and thought about converting it to a 300. I know the bore and stroke are the same and figured that it might be possible.Do you know if the reed valves are the same.

 

[OBJ]

Re: more horsepower

Appears they are Rude from the parts list. Both have the same part numbers for reed blocks and cages.

 

[vidar]

Re: more horsepower

if you are going to overhaul the engiine i woud remove all casting flaws in ports and so,trim all gaskets in the intakesystem put in boysen reeds and finetune the engine...then you woud be close to 300 cause the engines are pretty ruff inside normally compared to hi-perf-2strokes...10to15% hp diffrences from motor to motor is common on many...

 

[Dhadley]

Re: more horsepower

The first thing to determine is if you are getting the most out of what you have. If you arent then you may be spending money simply to be disappointed.<br /><br />Tell us more about your set up now. Top rpm with an average load, top speed, water pressure, type and design hull, propeller etc.<br /><br />IE -- if you only are turning the 250 to 5000 then putting in the 300 port timing isnt going to do much.<br /><br />Good luck!