25 HP 4 stroke vs 40 HP 2 stroke???

[wjhuskey]

Hello all. I have a 1961 runabout that was my Dad's boat and I've been wanting to get it back on the water for years. It originally had a Johnson 40 HP 15" shaft. I don't want to build the transom up and I also want to go with a 4 stroke. Looking at buying a low houred Suzuki 25 HP 4 stroke. I know 4 strokes weigh more and that's why I'm thinking the 25 HP 4 stroke will be a good replacement for the original 40 HP 2 stroke...plus these come in the 15" shaft. My big question here is how do you expect these two to compare in power to push this 14 ft fiberglass boat? I know 4 strokes sometimes seem to out power the same HP 2 strokes but I've heard it both ways. Can I expect similar performance as the original 40 HP 2 stroke???

 

[jimmbo]

With the Extra Weight and a Drop in Horsepower, I can't see how you would expect Similar Performance. Even a Crank Rated 40hp 2 Stroke will leave a Prop Rated 40hp 4 Stroke far enough behind that you could be across the Lake and Back before the Prop Rated 4 Stroke could overtake the 2 Stroke,

 

[matt167]

I literally did this exact swap on an aluminum StarCraft Holiday 14. It had a big twin 40. I put on a Suzuki DF25A. They weigh within a couple pounds of each other.

The boat’s top speed is almost identical to what it was but hole shot suffered a little. All in all for my purpose it was a major upgrade. I could get a 30hp ECU and remove the 25hp restrictor in place of the 30hp spark arrestor and probably get most of the lost hole shot. Zuki doesn’t build the 30hp in a short shaft

 

[airshot]

Newer motor is bound to perform better, but...if both motors were at peak performance, the 2 stroke would leave it in its wake. My neighbor and I have similar 16' aluminum boats. His a tracker and mine a Sylvan both with side consoles. He has a 50 hp Honda 4 stroke and I have a 40 up Merc 2 stroke. His top end is 26-27 mph, and mine is 30-31 mph all GPS speeds. My hole shot is quicker than his. The difference in fuel usage when making the same trip ....his uses 2-3 gallons and mine uses 3-4 gallons.

 

[flyingscott]

I literally did this exact swap on an aluminum StarCraft Holiday 14. It had a big twin 40. I put on a Suzuki DF25A. They weigh within a couple pounds of each other.

The boat’s top speed is almost identical to what it was but hole shot suffered a little. All in all for my purpose it was a major upgrade. I could get a 30hp ECU and remove the 25hp restrictor in place of the 30hp spark arrestor and probably get most of the lost hole shot. Zuki doesn’t build the 30hp in a short shaft

So your 4 strk is Almost equivalent to a 60 yr old 2 strk?

 

[racerone]

About 20 lbs more.-----And prop rated power.

 

[matt167]

So your 4 strk is Almost equivalent to a 60 yr old 2 strk?

If it were a 30hp I would think it would be very close. I lost the bottom end a little where I couldn’t pull a skiier now I don’t think ( we don’t anyway ) but the fuel savings and being whisper quiet are things that make me not regret it one bit

 

[matt167]

About 20 lbs more.-----And prop rated power.

As I recall, the DF25A short shaft was within a few pounds of the RD28

 

[racerone]

About 20 lbs in my opinion.

 

[jbcurt00]

About 20 lbs more.-----And prop rated power.

Important to note, racerone is correct. If the 40 2stroke is crank rated, it's more like a 35 prop rated, not in perfect running order, perhaps more like a 30 prop rated.

I've captain'd a 50s runabout with a Suk 25hp short shaft, it was near perfect, esp If it's got tilt & trim, and it did.

 

[jimmbo]

A 2 stroke crank rated 40 will blow the doors off of Prop Rated 25hp 4 Stroke
Heck a Crank Rated 20hp 2 stroke would beat the 25hp Prop Rated 4 Stroke, except in top speed, but the 20 would be across the lake and back before the 25 would hit top speed

 

[cyclops222]

A 2 stroke fires every revolution. A 4 stroke fires every other revolution
Who has pushed the boat more times and farther in 5 seconds ?

 

[JimS123]

Over the past 6 years I traded in 2 older boats and upgraded to Mercury 4-stroke outboards. Not just the mains, but 2 new kickers as well.

Never mind the capital cost penalty, I get it. Fuel economy increase, yeah.

At any rate, all I can say is holly mackerel.

They say, 4-strokes are dogs. When I punch my 60 she jumps on plane. When I punch my 150, I need to be holding on so the whiplash doesn't throw me on the floor.

In each case, after a cold snowy Winter the first time back in the water when the ignition switch is turned on it's an immediate click....zoom. No smell, and silent running.

Once again, yeah it cost me, but you get what you pay for and happiness is all that matters.

(Just my opinion and being retired I have little time left to tinker and worry about anything.)

 

[cyclops222]

I love 4 stroke being so much quieter.

 

[jimmbo]

I prefer the 2 Stroke, better hole shot, the Sound, and the Sweet Smell of the Burnt TCW Oil, plus the added Bonus of Mosquito Control

 

[airshot]

I love 4 stroke being so much quieter.

Can't speak for the new models, but neighbor has a Honda 4 stroke that is only barely quieter than my Merc classic. At wot we can carry on a conversion without yelling on either boat. Unless new motors are different, I don't see much difference.

 

[wjhuskey]

Important to note, racerone is correct. If the 40 2stroke is crank rated, it's more like a 35 prop rated, not in perfect running order, perhaps more like a 30 prop rated.

I've captain'd a 50s runabout with a Suk 25hp short shaft, it was near perfect, esp If it's got tilt & trim, and it did.

Jbcurt00, glad to hear this. That's the only thing holding me back on buying the motor is wondering if it'd be a waste of money because performance wouldn't be satisfying...and I'm not just talking about hole shot and top end speed (I'm not as worried about those things) but the way the boat handles and everything else because I made the mistake of putting a 55 hp 2 stroke on it and there was a weight issue with it. The boat isn't very stable as is since it's only 14 ft and doesn't have the higher end floatation like some brand of boats. Also, the short transom is something I want to leave as is. Its a fiberglass boat which makes it heavier than most 14 ft boats...so not just any motor is right for this boat. Even with the original 130 lb motor, my dad said it always acted heavy in the back. Now, wanting the 4 stroke advantages leaves me worried about the weight as well.