how to soup up my '73 25hp johnson

[Chinewalker]

Re: how to soup up my '73 25hp johnson

The problem with trying to do it to a clamshell cowling motor is the cylinder heads won't swap over. The 25 head is later style without the "ears" for the cowling supports, plus it has the thermostat which the '57 block won't support. Earliest model you could (easily) do the upgrade to is a '59...

 

[1946Zephyr]

Re: how to soup up my '73 25hp johnson

yea, good point. I forgot about those features

 

[R.Johnson]

Re: how to soup up my '73 25hp johnson

Power, and speed only depend's on how much you want to spend.

 

[Howard Sterndrive]

Re: how to soup up my '73 25hp johnson

talked to a knowledgeable guy at a local shop yesterday. He said there are lots of easy mods, but the first thing you MUST do to the 22 ci motor to hotrod it, is go to the megaphone style exhaust. Backpressure through the exh. housing prohibits any gains.

 

[1946Zephyr]

Re: how to soup up my '73 25hp johnson

Oh yea. You know how awesome those megaphone style exhaust headers would look on a 1946 Zephyr?

 

[F_R]

Re: how to soup up my '73 25hp johnson

talked to a knowledgeable guy at a local shop yesterday. He said there are lots of easy mods, but the first thing you MUST do to the 22 ci motor to hotrod it, is go to the megaphone style exhaust. Backpressure through the exh. housing prohibits any gains.

And put on a "quickie" racing lower unit. That one that comes with the motor is about as streamlined as an old boot.

 

[kenmyfam]

Re: how to soup up my '73 25hp johnson

Sure, if you buy enough parts. Actually, I have already done it. I gained about 2MPH. I'd say it wasn't worth it.

EDIT: But then I replaced the motor with an '84 35hp and it made a huge difference. Now it runs like the proverbial Striped Ape.

That's the best response so far !!!!

 

[Willyclay]

Re: how to soup up my '73 25hp johnson

When I was a pup, I found some go-kart tuned exhaust headers that exactly matched the exhaust housing bolt pattern on my 1947 Mercury KD-4(S). The sound was incredible; at least that's what the USCG CPO said when he directed me to "get off his water". Something about races only!