Modify 1984 65HP commercial

[budsbud66]

I got an awsome deal on a crated 1984 65HP (triple) commercial evinrude... however.. with a full fuel tank and livewells stackd' it can not plane my boat.<br />i have futsed with the props a bit but thier really is no replacement for more power...<br /><br />My question being... I modify the crap out of two strokes all the time.. does anyone know any tips or tricks that will help me get the horsepower up...<br /><br />my 600cc triple gets close to 130hp, and its half the size.. come on guys.. there has to be a few things holding this motor back.. <br /><br />Compression is at 130. on all three.. can these heads be shaved? is their a way to modify the exhaust? Do they make reeds for evinrudes? is thier jets to be screwed around with? would it be worth it to put on a different type of air intake system.. <br /><br />please guys something has gotta give this dog a little more juice!

 

[WillyBWright]

Re: Modify 1984 65HP commercial

Welcome to iboats. <br /><br />What RPMs are you gettng at full throttle? What pitches have you tried for props? A Commercial motor may have an unusual gear ratio made for heavy loads rather than speed. Describe the boat and how many Hp is it rated for?

 

[budsbud66]

Re: Modify 1984 65HP commercial

Prop:<br /><br />I know the prop pitch works best at a 15, ive tried a 13,17 <br />17 would not plane at all.. 13 and 15 didnt have much difference except i lost top end.. <br /><br />Boat: <br /><br />The boat is a 16ft 1995 fiberglass starcraft It aint light, but the guy i got it from said he got 37mph out of it.. another guy with the identical boat had a 1995 60hp merc and he said he got 35, with no trouble planing..<br /><br />The boat i got with the older moter from the guy who put it together with a crate motor that was sitting for years and years. (Definately could tell he was not lieing, guy did have his own boat sales shop and the motor was A1 clean as heck)<br /><br />So anyways right with ideal chop, low fuel, jsut me driving i can pull 31mph, out of it.. planes out decent when im alone. but certainly not normal.<br /><br />The boat is rated for 65hp max, and thats whats on it...<br /><br /><br />when i go to drive the boat on the trailer, there isnt enough power to push it all the way up.. just sits at low rpm, <br /><br />i suppose i should put a tach in.. that would definately be a good first step because i have no idea what the rpms are at,<br /><br />What is the ideal RPM for this boat?<br /><br />can i shave the head to get the compression ratio up to 10:1 ?????<br /><br />Could there be an issue with the Carbs??<br /><br />If there was a way to slam a pipe and reeds on i bet the motor could make darn near 120hp, maybe i dont know the mechanics of boats like i do sleds.. <br /><br />thanks for any help..

 

[BillP]

Re: Modify 1984 65HP commercial

The 65 commercial has a thicker head that lowers compression and lets you run down to 67 octane gas. It also robs 5hp. This is basically a detuned 70 domestic motor. Carbs and lower unit are the same as the 70hp domestic. I don't know for sure but if you put on a 70 domestic head, the carbs may need rejetting too. <br /><br />I have a 65 commercial on a 17' outboard and it clocks 30+ mph with fuel, fishing gear and 2 people. Put 4 people in the boat and it takes a little time to get over the hump. If memory serves right the rev limiter starts ticking at 6600rpm...easily attainable on mine when trimmed up and running light.

 

[budsbud66]

Re: Modify 1984 65HP commercial

Well there is no way the compression is 130! the guy that i had install the powerpack must have not checked.. i doubt compression is even at 90psi..<br /><br />I like the optimisim in saying its a detuned 70hp.<br /><br />Can anything with the exhuast be tampered with. that really is the key to making gobs of power on a two stroke.<br /><br />do the 65 / 70 / 75 's all have the block? bore/stroke?

 

[budsbud66]

Re: Modify 1984 65HP commercial

BillP may i ask what pitch prop you run??<br />mine is 13 3/4 / 15p<br /><br />This may be a dumb question, but would it be dumb to go down in size and up in pitch? <br /><br />And what produces more top end speed, the aluminum prop because its light, or steal prop because it has no flex?<br /><br />i may as well buy a new motor because i need more holeshot, but i want more top end.. i know im going to have to sacrifice somewhere..

 

[BillP]

Re: Modify 1984 65HP commercial

My prop is an OMC stainless and has no markings. I bought the motor from an OMC rep and he sized the prop...it worked. The pitch lets it run at 6300...and when trimmed up it ticks the rev limiter.<br /><br />Except for the low compression head, internals of a mid 1980s 65 commercial and 70 domestic block are 100% identical...same bore, same stroke, same specs, same everything. Differences are on the outside. Commercials came from the factory sans VRO.

 

[ob15]

Re: Modify 1984 65HP commercial

We still don't what your WOT rpm's are. With out that we can not relly help too much. Post the WOT rpm's & we'll help you get it going

 

[tashasdaddy]

Re: Modify 1984 65HP commercial

how does the cavitation plate line up the the hull?

 

[budsbud66]

Re: Modify 1984 65HP commercial

well, i wont be able too get WOT RPMS till later this month.. everything is still froze up tight around here.. I really think finding this forum was a blessing.<br /><br />The cavitation plate lines up equally with the pad on the bottom of the boat, how ever, the boat never really rides on the pad, once i get the boat out of storage i can take pictures and get more accurate numbers.. Now im getting real excited. ( No more making my fishing partner run to the bow to plane it out..) <br /><br />thanks guys.. <br />also can these heads be shaved? i have access to free machine work, (well it costs a case of beer)

 

[ob15]

Re: Modify 1984 65HP commercial

You may not need to do anything other than adjust the setup of the boat. The WOT rpm are an absolute must to help tweak the setup. Does the motor have tirm & tilt?.

 

[budsbud66]

Re: Modify 1984 65HP commercial

yes power trim. there is a "whale-tail" on it. and it does help get the boat out of the water.