Home › Forum › Ask A Member › History of the FD Johnson series › Re: History of the FD Johnson series
Don’t believe everything you hear. Even me. But if you will listen, the 18 and 20 were the same engine, but with a bit higher compression in the 20. As for the carburetor, I think they were the same, but can’t swear to it without measuring the venturiis. That stuff about rejetting is BS. 18 and 20 were made in the same years, so it isn’t the way they measured it either. As for the 25, there were a number of changes. Different pistons, different cylinder head, different exhaust tuning, different carburetor, etc. Don’t you dare to think you can make a 25 from an 18 by swapping any one thing. You will probably make it worse. If you want the fastest FD (22 cubic inch), get at 25 to begin with. Better yet move up to a later model with thru-the-prop exhaust. Or just get a 35 and be happy.