Converting a 20 HP Johnson to 35 HP

[martijn]

Re: Converting a 20 HP Johnson to 35 HP

The lower units will not swap on a the 76 thru mid 80s models. http://rides.webshots.com/photo/2609670230101354590ozLxGB The bolt patterns are different as are the midsections. Also the Cylinder heads are different.

they can be swapped , the bolt pattern directly under the engine is the same
both are fitted with only 5 bolts
( i meant complete lower section with the middle section ,sorry )

on my two engines the cilinder heads were the same .

 

[Wurframen]

Re: Converting a 20 HP Johnson to 35 HP

Had to register to give some my personal experiences.
Swap is possible,made it.Kept smaller gear and putted faster propeller.
Hard to find ,at least here in europe.
It can take the punishment(so far..knock knock)

Swapping 20 power head to 35 can be done and do all the tricks to get 30 from it.

One point what i did not see in the previous posts are the reed valves.
Mine 20 and 35 had different ones.35 obviously better ones.
So change those too.
And when you really want to get it fly....little tuning with valves,shaping and lightening them(be careful with originals to avoid breakings).
Easier the valves open, more air/fuel you get in.
That was for a fun long time ago when i played with those also in dirt bikes.
Hope this helped.

-81 50 lies in pieces...new bearings came friday...
Bearing set in shop europe 890?....from US around 200? with shipping.
Tooked bearings from US and bought something from shop.
-85 70 and -79 35, both have light starting bearing problem.
Manager told "no need to repair,too costly"...not with these prices and the labour rates here (80?/hour)
Paid 50? totaly with cables,something to do at the wintertimes.

And for fun..heres traditional finnish fishing boat.
Filmed also in Pokerrun-competition.
Well..not so traditional boat from 1958.

http://www.friddemartin.net/fanny/videofi.html

 

[zz_denis]

Re: Converting a 20 HP Johnson to 35 HP

I have a late 70's 20hp Evinrude which seems to have been made in Canada. BRP's parts website doesnt even list a 20hp for this time period. Is the block/head of this motor also identical to later 80's 35 hp motors?

 

[Chinewalker]

Re: Converting a 20 HP Johnson to 35 HP

zz-denis,
Your motor is a 22-cube model and there is no way to bump it up to anything more than a 20hp. It is similar to the 25hp of that era, but would require a complete overhaul with the 25s crank, pistons and cylinder head to get there. Much easier to simply get a bigger motor.

 

[MadtownWI]

35HP Johnson HP increase

35HP Johnson HP increase

Hope someone is still monitoring this thread. I have a 1982 35HP Johnson model J35ECND. After reading for hours about upgrading the 20 to 25 or 30 and 35, I still haven't seen a post about upgrading the 35HP. My motor runs about 22-23 on a 14 foot fiberglass Sea Nymph V-Hull with a 10.5 X 11. Plenty of power and sounds about max RPM. So with so much power I put a 10 X 13 pitch on it. Now it's slower with less RPM...naturally without extra power. I'm hoping to gain some HP for faster speed with the 13 pitch prop.

Back to everyone's past posts. My intake manifold looks to be half the size of the exhaust of carb. Other than expanding the manifold to fit the carb, what else can I do to increase the 35HP.

 

[MadtownWI]

35HP Johnson upgrade

35HP Johnson upgrade

OK, had to try the upgrade. Bored the intake manifold to 1 3/8 like the exhaust of the carburetor. I used the plywood jig as described in this thread earlier. I used a wood hole bit from ACE for 4.50, new manifold gasket for 2.25...gained 5 mph for under $10. Cannot beat that. It does over rev with the 10.5 X 11 so I put the 10 X 13 on it. Now up around 30 when only got 22-23 before bore increase. It does run better at idle too.

Just want to share my experience. If anyone has another upgrade to the 35 other than the intake, let us know.

 

[Chinewalker]

Re: 35HP Johnson upgrade

Re: 35HP Johnson upgrade

Madtown - your motor sounds like it may have been cobbled, as the normal intake for the 35 should be the same size as the mounting flange side of the carb...

 

[MadtownWI]

Re: Converting a 20 HP Johnson to 35 HP

Well then the factory must have installed the incorrect manifold. This engine has never been taken apart. The paint all around the manifold was never disturbed, no cracks and the paint still rounded in all the seams. Go figure. Serial numbers match all around. This thing is almost brand new, every inch shines, must have been stored indoors every minute not in use.

 

[evinrude20]

Re: Converting a 20 HP Johnson to 35 HP

Here's a question...how much of a difference in speed is there between upgrading with the conversion, or just putting a 35 motor on?
IE>

20hp block to 20hp block (w/35 carb bolted on) speed gain
vs
20hp block to 35hp block speed gain
Any ideas?

 

[johnsonrude20]

Re: Converting a 20 HP Johnson to 35 HP

Just did this over the weekend. Awesome!! Before conversion: me and fishing gear and camping supplies for 4 days and 20gallons fuel=14mph. Just me=19/20mph. Haven't loaded boat down yet but with me and buddy in boat on a very choppy lake=28mph. Unbelievable hole shot! Can't believe the difference in power. Gonna go with a 13p 3 blade now instead of the 11p 4 blade composite I have now. Speeds checked by GPS. Did not run boat with just me.

 

[dennisporter]

Re: Converting a 20 HP Johnson to 35 HP

wow there is alot of expertise to tap into on these thread. Any thoughts on how these learnings can be transferred to a '93 Johnson 20HP. From my quick observation, there is 35HP carb kit for my model as well.

Sounds like it is worth it to many who tried it and I am encouraged to go for it.

 

[blimp]

Re: Converting a 20 HP Johnson to 35 HP

You have to swap out the entire carb + manifold, not just get a carb kit for a bigger carb...

 

[zz_denis]

Re: Converting a 20 HP Johnson to 35 HP

Hello,

In post #35 , Sandhammaren mentioned that 76+, 77+, 85+ motors have interchangeable parts.
I have a 1994 20hp Evinrude. I compared the part numbers with a 35 hp model, and block/pistons/crank/etc seem to be the same.

Would this motor (1994 model) be a good candidate for the carb and intake swap to gain 15 hp?

Another question:
It seems that sometime in mid 80's two things happened - they went to a primer system as opposed to butterfly choke, and they started rating the motor output at the prop.

Do i HAVE to get a 1985+ primer carb for this upgrade? Would it be possible to use an earlier butterfly choke carb?
Also, if i take parts (carb +intake manifold) from a 1994 (same year as mine) 35 hp, wouldnt it be equivalent to pre 1985 40hp (back when hp was rated at the engine)?
Does this mean that my 20 hp (with a newer 35hp carb) would actually be more powerful than older 20hp's with the same upgrade?

Thanks!

 

[Chinewalker]

Re: Converting a 20 HP Johnson to 35 HP

Not quite. The 30 and 35 from 1994 had the same carburetor and intake manifold... I think when they re-introduced the 35hp (33.1 cube) motor in the 1990s they were relying on the fudge-factor in the horsepower rating system. In my experience, the 1990s 35hp wasn't any different, performance wise, than the pre 1985 35s. More than likely it was marketing, as 35 was a popular size.

 

[ChrisAG]

Re: Converting a 20 HP Johnson to 35 HP

I have a 1995 Johnson brochure, and for at least that year they didn't offer a 35 - the engines were 20, 25 & 30hp.

All three had identical displacement and thru-the-hub exhaust. The 20 & 25 were rated at 5000rpm, the 30 at 5500rpm.

I suspect the 30 was unchanged from the earlier 35.

 

[dennisporter]

Re: Converting a 20 HP Johnson to 35 HP

I took the advice of the thread ( I had a previous post) and purchased a used carb and manifold for my Johnson 20HP (TE20CRLETS 1993). I am certain the carb is from a 30HP Johnson E30ELENR 1992. I've installed the "new" intake manifold and I am about to "rebuild" the purchased carb the typical repair kit. I just want to have new parts for before I install it.
According to the repair manual for this engine block, the difference between 25HP and 30HP is BOTH a timing change and carb change. I'd like to keep the timing as is for now (single variable change) and just add the larger carb to see if there is an increase in power/speed.
HERE IS THE PROBLEM:
I don't know which orifice plugs to select because I am running a larger carb on smaller engine block. I expect the orifice recommendations for carb will likely supply too much gas/air to the smaller block.

Any suggestions?

 

[viciousfishes]

Re: Converting a 20 HP Johnson to 35 HP

So what kind of carb would I need if I wanted to do this with my 1968 20 hp Johnson? Im getting all worked up reading the thread and Im deifinatly going to give it a shot if possible...

 

[blimp]

Re: Converting a 20 HP Johnson to 35 HP

I don't think it'll work for a '68. That is a different block, already a hopped up 15 hp.

 

[blimp]

Re: Converting a 20 HP Johnson to 35 HP

I don't know which orifice plugs to select because I am running a larger carb on smaller engine block. I expect the orifice recommendations for carb will likely supply too much gas/air to the smaller block.

Any suggestions?

Just use the orifice plugs (jets) that come with the 30hp. The blocks are identical.

 

[mahutane]

Re: Converting a 20 HP Johnson to 35 HP

Lucky me after finding this thread I have decided to do the mod on my Johnson that i just bought from e-bay, to my surprise its already been done.