tahoeguy318

I was on my fathers boat the other day and he put the throttles all the way down I noticed that both engines maxed out at 4100 rpms...he is alwasy complaining about how slow the boat is and how much gas it eats..I asked him about that and he said "its always been that way thats how its suppposed to be"I know its an old heavy boat but my smaller formula revs at 5000 rpms...His boat is a 1985 28 pc formula I don't know how much it weighs but I its 28 feet long 10' beam...it has twin 260 mercs that have been recently bored and rebuilt. I think it had 19 pitch props but I am not sure...its this the right rpm for his boat ...its seems really low to me and I think it should be at like 4600 ok thanks alot Harry

It think he should switch to 17 pitch props, will that help his cruise speed and gas mileage

tahoeguy318

nobody knows what peak rpm is for a 1985 350ci 260 hp mercruiser???

ajl marine

im suprised he hasnt burnt a hole in a piston yet .350ci wot rpm is good between 4700-4850.----yes i would definatly be fitting a smaller pitch prop to unload the motor,this will also get you on the plane quicker and improve cruise speed and fuel economy . general rule of thumb is - for every change of pitch in prop size you will lose or gain ( in theory ) between 150 - 200 engine rpms . depending on which way you go

MESABALANCING

Back when I worked at Custom Engine Service back in the 80s we used to set up all stock engines to a wide open throttle speed of 5200 rpms and thats what we found to be the best for speed and economy if you look at the rating plate on the engine it will tell you what the hp rating is at and believe me when I tell you thats the way the engines will perform best this doesn't mean you have to run them at that rpm you can cruise them anywhere you like the exhaust temps at the engine speed you have now are very high because of the fuel consumption you have you should prop to the max engine speed . Good luck Laz