'50's model 25-35 hp questions

Was over in props talking about things and the subject of OMC cubic inch displacement came up concerning the old twins that started out at 25 hp (with the sliding throttle across the front and pressurized fuel tank) up through the twin 35's of roughly the '58-59 era.

Many a time, as a youngster, I'd see one of these engines, even the 25 hp, on the back of a 14-16' wide beam wooden boat with 2-3 fishermen/women full of gear, blast of across the water doing a respectable speed like 20 to 25 mph. Wife's family had a 35 on a 14' wood runabout and it would tug a pair of skiers at a fast enough clip to have fun.

I know they turned a pretty large dia prop (12-13"?) with a pretty shallow pitch (10-12"?), and as I remember the engine rpm max rating was like 4500.

I always thought they did it with a lot more cubes than Merc used at the time for the same hp. What I'm seeing today in the other post is that the cubes weren't all that big and that they turned a high gear ratio lower unit, so all that low end thrust came from the gear reduction per se, not the "big block" syndrome.

The Mercs of the day were 4 cyl Mark 30 or Mark 55 at 30-40 hp and I remember them having higher rpm limits (they screamed while the OMC's were very quiet) and had a smaller, higher pitched prop.

So I guess their gears were more like 2:1 whereas the OMC was 2.4 something:1. One thing was for sure and that was the OMC could pull circles around the Merc, but on a light fast boat the Merc was tops. (Heck, I was just a kid, I didn't know anything about specifications....so I don't have any real numbers of my own.)

Used to have the Old OMC site from a guy in Germany and it had all the specs and brochures and all, but I can't find it anymore.

Thanks,

Mark

Re: '50's model 25-35 hp questions

and we used to have a saying years ago.
if it starts that merc is the fastest thing on the lake, if it doesnt Ill come get ya with my big twin 40 .
its amazing the technology shift from the days of the oldmerc dock busters and the OMC fat 50 of 1958 to present day F350 V8 outboards.

Re: '50's model 25-35 hp questions

Texasmark said:

Used to have the Old OMC site from a guy in Germany and it had all the specs and brochures and all, but I can't find it anymore.

Thanks,

Mark

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The Old-OMC site: http://www.old-omc.de/


When I was young I was a devout OMC fan, while another friend was a devout Mercury fan. Both sides had their star players and both sides had their drawbacks. Today it is easier to work on and restore an OMC outboard than a Merc. I am still a huge OMC fan but I admire all the big (and small) manufacturers for their contributions

Heck, I even used to like the Chrysler outboards back around the time when they made a 150-horse, compared to Merc's 140 & OMC's 125. Chrysler used to had their own advances in outboard design as well, plus they also had their mistakes as well. Today the old West Bend / Chrysler / Force brand is an orphan.

Re: '50's model 25-35 hp questions

The old 25's (1951-55) were 35.70 cid as were the 30's (1956) and the 35's (1957-59) were 40.5 cid. The 40's were a whopping 43.9 cubes

Re: '50's model 25-35 hp questions

1946Zephyr said:

The old 25's (1951-55) were 35.70 cid as were the 30's (1956) and the 35's (1957-59) were 40.5 cid. The 40's were a whopping 43.9 cubes

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Thank you sir.

So you just supported my assumption that the early "Big Twins" were good hole shooters because they were heavy in the cubes even though they ran high ratio gearboxes and large diameter props for the hp and era. And I am going to print your reply and put it in my permanent files.

Mark

Re: '50's model 25-35 hp questions

Cool. Here's you some more:
33hp 1965 - 197? 40.5 cid
28hp 1962 - 1964 35.7 cid
25hp 1969 - 1976 22.0 cid
20hp 1966 - 197? 22.0 cid
18hp 1957 - 197? 22.0 cid
15hp 1953 - 1956 19.94cid
10hp 1949 - 1963 16.6 cid
9.5hp 1964 - 197? 15.2 cid
7.5hp 1949 - 1958 12.4 cid
6hp 1965 - 197? 8.84 cid
5.5hp 1954 - 1964 8.84 cid

The motor years with question marks are called out in one of my other manuals and that is out in my shop......darn. So here is some more helpful info for you.

Re: '50's model 25-35 hp questions

I was always a Ford guy and my best buddy was always a Chevy guy. I was always a Johnnyrude guy and my best buddy was a Merc guy. Guess that kept the relationship interesting. I remember those old Mercs always beat the Johnnyrudes of comparable horsepower on the top end. Made me so mad to admit that a Merc was faster. But I could pull two skiers behind my 14' Glasspar with a 40hp Evinrude, and we always preferred my boat for skiing rather than my buddy's boat with a Merc. That old Glasspar would do 33 mph with me alone in the boat. Now I have my new (to me) 1961 14' Starcraft with a 45hp Merc, and it will do 35mph with me in it alone. So I guess there wasn't that much difference between them. But the Rude did run at about 4500rpm and I notice my "new" Merc runs about 5500-6000 rpms. Maybe it would run faster if I was at the same weight I was when I was a teenager.
I think I weighed about 100 lbs. when I learned to ski behind my cousin's 14' fishing boat with a 16hp Oliver motor.

Re: '50's model 25-35 hp questions

yea, I own a 1970 Ford truck myself.

Re: '50's model 25-35 hp questions

1946Zephyr said:

Cool. Here's you some more:
33hp 1965 - 1970 40.5 cid
28hp 1962 - 1964 35.7 cid
25hp 1969 - 1976 22.0 cid
20hp 1966 - 1973 (1976 in Canada) 22.0 cid
18hp 1957 - 1973 22.0 cid
15hp 1953 - 1956 19.94cid
10hp 1949 - 1963 16.6 cid
9.5hp 1964 - 1973 15.2 cid
7.5hp 1949 - 1958 12.4 cid
6hp 1965 - 1979 8.84 cid
5.5hp 1954 - 1964 8.84 cid

The motor years with question marks are called out in one of my other manuals and that is out in my shop......darn. So here is some more helpful info for you.

Click to expand...

Notice that the 40 horse has a 43.9 c.i. displacement, larger than the 50 horse of 1971 - 1975 (41.5 c.i.d.). I love the old 40s as well; they're simple, torquey and understressed.

It's funny how the 28 was really the old 30 (35.7 c.i.d.), and the 33 was really the old 35 (40.5 c.i.d.)

Re: '50's model 25-35 hp questions

Yes, and the 40's I have learned are a lot better engines than the later 50's were too. They got their increase of horse power by having a dual carb set up, and electronic ignition eventhough they were less cubes than the earlier 40's. They were a newer technology design, (like the V-4 and L-3 models)but had a couple issues. The 55hp L-3 was about one of the biggest night mares for trouble shooting, but fortunately they quickly upgraded things when the 70hp L-3 came out, which was only a couple years later. 1969 was a redesign year for the V-4 models, but those were decent engines.

Yes, I think you're absolutely right about the 28's and 33's. I worked on a few of those and the only thing different from the motors of the 50's, was the shroud set up. The powerhead, leg and lower units were almost identical to the 1956 - 57 Big Twins.. Too bad they only made them for a few years.