Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

[benga]

Hello.
I have made a modification on my 1984 Evinrude 20 hp in order to increase the power. No spare parts need to be purchased to do the modification.
I grinded the manifold inlet to the same size as the carburetor diameter.
Exactly how I did it, is a bit to long to submit here, so I include a link to my homepage instead.
Here is the link. http://www.rapps.se/bengt/evinrude/evinrude.html
Best regards.
Benga

 

[jbjennings]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

Now that was an informative piece of work. Excellent pictures and explanation.
Maybe I'll try this myself one day!
Very ingenius,
JBJ

 

[wbeaton]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

This modification will only work on the years where the intake manifold was the only difference between the 20 hp and 25 hp OMC's. If anyone decides to try this on their motor I suggest you check the BRP website and make sure the intake is the only difference on your motor. Some years also required a different carb and perhaps other things. Also, I think some of the European 20 hp OMC's from the middle 1980's came stock with the 25 hp carb, where North American ones didn't.

Thanks for posting. It was an interesting read.

 

[benga]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

This modification will only work on the years where the intake manifold was the only difference between the 20 hp and 25 hp OMC's. If anyone decides to try this on their motor I suggest you check the BRP website and make sure the intake is the only difference on your motor. Some years also required a different carb and perhaps other things. Also, I think some of the European 20 hp OMC's from the middle 1980's came stock with the 25 hp carb, where North American ones didn't.

Thanks for posting. It was an interesting read.

Hello Wbeaton.
Yes I agree that it is best to check the differences between the different models in the original parts catalog. Now when Bombardier has been kind to offer free access to the online catalogs, for all people with internet access, it is a quite simple task. This was very easy in my case where all parts on my 20 hp motor had same item number as the 25 hp motor except for the intake manifold. I had my motor type number ready when i did the check. I do not think that we have other OMCs in Europe as I have not seen any special model numbers in BRPs online catalog. I guess that the power increase modification is possible for most people with a 20 hp OMC from mid 80s.
It worked for me at least.
Benga.

 

[wbeaton]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

No they are the same OMC's, but I think the 20 hp carb is different in Europe on some mid 1980's OMC's. I had a link to another (Italian?) site about increasing the horse power of the 1980's OMC 20-30 hp motors, but I seem to have lost it. I probably earsed it during the "Great Purge of 2006".

 

[water n oil]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

Would any re-jetting/tuning be necessary on this mod?

 

[benga]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

Would any re-jetting/tuning be necessary on this mod?

As I see it the answer is no.
The nozzles for the 20 and 25 Hp motors has same part number.
I have not changed any nozzles and the motor runs very well.
I tested the boat yesterday an it run well over 6000 rpm. with a 13" propeller.
I had a digital optical tachometer to measure the rpm.
This gives gives a good speed on the boat of up to almost 30 knots.
I didn't dare to give the motor full throttle.
Not bad for a motor that is sold as a 20 hp motor.
I will try to find a 15" propeller to avoid to run the motor on to high rpms.

 

[water n oil]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

As I see it the answer is no.
The nozzles for the 20 and 25 Hp motors has same part number.
I have not changed any nozzles and the motor runs very well.
I tested the boat yesterday an it run well over 6000 rpm. with a 13" propeller.
I had a digital optical tachometer to measure the rpm.
This gives gives a good speed on the boat of up to almost 30 knots.
I didn't dare to give the motor full throttle.
Not bad for a motor that is sold as a 20 hp motor.
I will try to find a 15" propeller to avoid to run the motor on to high rpms.

Sweet...

 

[simplystressed]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

Time to revive this thread, anybody know what years this was possible in to do? Without additional parts?

 

[boobie]

Re: Convert your 20 hp evinrude (OMC or Johnson ) to 25 hp.

This thread is over 6 yrs old. Please read the rules at the top of the forum and Start a New One. Thank You.