2 cyl. omc 40 vs 50

[fast_c_class]

i just paged through the omc parts breakdowns to find the diffs in these to motors, but what i found isnt what i expected. i thought that the carbs would be different (all the inside parts are the same xcept low speed stuff).i also thought the reed and heads would possibly be diff, but nope. were is the 10hp or 20hp (60hp) coming from? are the carbs throats bigger? i see they use diff. plugs.<br /><br />i ask cause it is inevitable that the gearhead in me is going to convert it, just amatter of time. by the way this is a 92 motor

 

[fast_c_class]

Re: 2 cyl. omc 40 vs 50

by the way, i just bought the motor after searching high and low for a clean motor so buying a 50 hp is out of the question. i understand some of you frown upon doing this because it is a large undertaking but i like doing stuff like this. also i need to make power with the 2cyl cause going 3cyl is out of the question (boat cant take anymore weight hanging off the back of it) i want to get her into the 60's

 

[DSL DOC]

Re: 2 cyl. omc 40 vs 50

id like to see a reply to this from other fellow mechanics i as a full time pro mechanic always like to start with a large enough block assy to suffice for this type type of transaction but i dont see why you couldnt get 50 hp out of your 40 by maybe boring a bit and really cleaning her up most of the time like all other applications motors are underpowered esp due to emissions now will the transom take 50 hp and what would you really gain we all want to go faster but id rather have an awesome running 40 than an "always messin with" tweaked 40 know what i mean my motor is a 62 40hp flyin high they dont make em like they used to but it also matters what ur pushin ive clocked at 22-28 mph depending on the water with my 40 pushin my 16 foot 62 crestliner fiberglass ne other opinions to see offer em up cya'll

 

[Lark40]

Re: 2 cyl. omc 40 vs 50

If you want speed, you want rpm's.<br /><br />OMC 40's (at least the old ones I work with) simply don't turn enough rpm's compared to Mercurys.<br /><br />Most outboard speed enthusiasts have Mercs. Maybe that is where you should start.

 

[fast_c_class]

Re: 2 cyl. omc 40 vs 50

ive heard that you can spin these motors to 6000 rpm, btw the boat went 40 mph with a 25hp, havent tried the new 40 yet but i think ill be wanting more power after this season, just thinking ahead. omc made a race version of the 2 cyl. block that made 60 some hp. so i know i can be done

 

[Lark40]

Re: 2 cyl. omc 40 vs 50

What year 40hp are you talking about?<br /><br />I have a 250 lb aluminum racer. With my 1960 40hp, it only goes 29 mph, turning 4400 rpm with a 14" pitch prop.<br /><br />And, that's measuring it with two GPS's and a TinyTach.<br /><br />Now, if your talking about a much newer engine, with a modern hp rating, that's another issue.

 

[fast_c_class]

Re: 2 cyl. omc 40 vs 50

i had an old big twin on it before with a 14 pitch prop and i topped out at 40mph , now i got a 1992 40hp with a 11x19 cupped prop, trying this combo tonight ill see how it goes

 

[sparkroost]

Re: 2 cyl. omc 40 vs 50

funny how people see that the difference between some models, say 40hp vs. 50hp, is the carbs. So.. they think that the since the carb is bigger that that's where there getting the added HP. Simply not true. A carb is a metering device that adds a mixture of fuel and air into a cylinder. Because your carb is bigger does not mean more fuel and air is going into the cylinder! Take a garden hose and try and stuff more water through it by opening the valve more. Once the hose is full, only so much water will go through it. <br /><br />The added horsepower comes from port volume and port height. There are also other ways to gain HP. Exhaust tuning, higher compression, head configuration, timing, etc..

 

[Lark40]

Re: 2 cyl. omc 40 vs 50

I know a guy who has a boat just like mine with a '58 Merc 55, which is 40 hp. It turns 5800 rpm.<br /><br />He can hit 40 mph, but not much over. He has run against similar boats with BigTwins/Larks, and he says they do about the same as mine (28-29).<br /><br />My question to you is: how are you verifying your speed? If not a timed and measured course or with a GPS, it is suspect. Water pressure gauges are about worthless in my opinion.<br /><br />For example, my Starcraft cuddy shows 55 on the Aquameter in the dash. But 39 on multiple GPS's, which are the "gold standard".

 

[G DANE]

Re: 2 cyl. omc 40 vs 50

As far as i´v been advised, the difference between 1988 40 and 50 Hp are the heads - ( can be changed by milling ) the reed stops ( get some from a scrapyard ) and some carb difference ( if it is lowspeed probly soesnt do much difference.<br /><br />Reed stops makes a lot of difference alone - i tried it !

 

[G DANE]

Re: 2 cyl. omc 40 vs 50

Be aware - the 50HP should be allowed to turn 500 rmps more of top rpm.