OMC 25 hp displacement change

[PugetSoundBoater]

When did the change to more cubic inches occur? ! have 2 25 HP motors ,a ’81 and a ’84 .Are these the larger displacement motors?
Thanks .

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[retiredoz]

Looks like ’76 was the last year of the 22 cu in motors. So yes, yours are the larger (same as the 35) 31.8 cu in…

[RICHARD A. WHITE]

I think some of the earlier 25hp’s were actually hopped up 20 hp motors

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[bullie]

quote Richard A. White:

I think some of the earlier 25hp’s were actually hopped up 20 hp motors

I was thinking something like this Richard. Very limited experience on my part but I was thinking they were very similar to the 18s. I may be way off. Hoping someone comes along and helps us out with the chain of development. I recently traded an early 70s 18 hp (great little motor) for a AR15 a buddy had. This same buddy, in his search for a boat to accompany his new motor, bought a 1448 yesterday that had a 1976 25 hp Evinrude on it. I was thinking they looked very similar under the hood but I am probably over simplifying the actual development. Waiting on some education….

He dropped the 25 off with me for a tune up/clean up. We got it running yesterday so it should be an easy one. But, now he has another problem. 2 motors and one boat. LOL He may catch our infection.

[RICHARD A. WHITE]

Reel him in slowly, lmbo 😆

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[PugetSoundBoater]

22 C.I to 31.8 C.I. is an increase of about 44.5 %. That is quite bit. Has the same powerhead as a 35 hp of the same year range.
Thanks for the info.

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[retiredoz]

At casual glance, it looks like the J/E 18s and the Johnson 20 also used that 22 cu in block. And the 25 till ’77..

[dan-in-tn]

The 1976 25hp was not the 32 cu in powerhead. That didn’t come on the 25 till 1977. The 35 came in 1976. Can be a little confusing. 1969 was the first year for the 25hp and the pistons, crank, head, & other things were all different. OMC has a tendency to build motors in families of engines (as most companies). The same engine powerhead is used with different carbs, heads, etc. to build different horsepower. Sometimes interesting things have to be done to hold the horses down or boost them up to meet the requirements. Usually the more horses you get from the same cubes the more fragile the motor becomes.

Dan in TN

[frankr]

Yep, they foiled you guys that think you can morph your 18 to make 25 horses, Well, you can, but not without changing a lot of parts

[vintin]

I believe the 1969 25hp was the first year for tuned exhaust in that size motor. I’ve got one and it runs great.

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