# Upgrading from 25hp 2-Stroke to 4-Stroke



## Florida_Native (Jul 28, 2016)

Greetings, 

I currently own a 16' Polar Kraft with a 97 25hp Evinrude 2-stroke. I'm looking to upgrade to a 4-stroke and want to maintain the same speed and performance. 

I've always heard that 2-strokes are faster than 4-strokes. The Yamaha salesman told me that the 2-strokes and 4-strokes are equivalent now days, but then again he may just be trying to sell me. 

If anyone has done a similar swap I'd like to hear what your opinions and experiences are. 

Thanks


Sent from my iPhone using Tapatalk


----------



## DaleH (Jul 28, 2016)

I can't speak to 25hp OBs ... but this season my boatclub replaced (_Huh? It was running fine, less it was a pull-start OB ..._) a Nissan 10hp 2-stroke with a new electric start Honda 15hp 4-stroke. These motors were put on the same heavy frp Carolina Skiff J12 hull for use as a club tender, 24/7.

It is an absolute DOG of a motor ... the Nissan 10hp was soooooooooo much faster than that goshdarn heavy Honda! Makes the J12 hull sit down at the stern and doesn't have enough ponies to get the hull up near, never mind on plane ... To me, I don't think that it's the HP per se that's at fault as much as the sheer weight increase and that it drags down the stern.


----------



## onthewater102 (Jul 28, 2016)

Check out some comparative info on NADA's website where you can compare weights of the two. I think they've dog piled so much crap onto the newer 2 strokes that they just don't have the same weight advantage that they used to.


----------



## Florida_Native (Jul 28, 2016)

Yeah my 2-stroke would be about a 50 pounds lighter than a new 4-stroke sukuki or merc. I wouldn't go with a yamaha, way to heavy. 

But still not sure, the motor I have now is a 97, I'm sure it's not running at peak performance. 


Sent from my iPhone using Tapatalk


----------



## Pappy (Jul 28, 2016)

To me......that is definitely not an "UPGRADE"
Your current engine is lighter and has better acceleration. 
Your current engine will probably out-perform the newer engine as well at WOT. 
Your current engine will be less efficient on fuel.
Your current engine will be louder at idle and off idle power settings. Pretty close at WOT.
The difference in economy vs. what you will be spending on the new engine will more than make up for the difference in fuel burn/cost for a long long time.


----------



## kofkorn (Jul 29, 2016)

Florida_Native said:


> But still not sure, the motor I have now is a 97, I'm sure it's not running at peak performance.



20 yrs old, that's barely broken in 

As Pappy I'm sure can attest, the motor age has a very small effect on the performance. Unless you have a tired motor due to thousands of hours of use, most performance issues can be corrected with proper tuning. Tuning which should cost you far less than a new 4 stroke will run. 

If you troll continuously, or want a super quiet motor, go for the 4 stroke. If you want good get up, and top end, stay with your current motor and get it running right. The new 4 stroke will feel significantly slower than what you have now.

Good luck!


----------



## Pappy (Jul 29, 2016)

I see you are from Florida? What part? 
Is your engine a short shaft or long?
Depending on what exhaust and gearcase you have on the 25hp you can dial up the horsepower pretty easily on your current engine. 
There is a thread on here about that and several members have done it.


----------



## Florida_Native (Jul 29, 2016)

Pappy said:


> I see you are from Florida? What part?
> Is your engine a short shaft or long?
> Depending on what exhaust and gearcase you have on the 25hp you can dial up the horsepower pretty easily on your current engine.
> There is a thread on here about that and several members have done it.



I'm in South Florida, it's a short shaft. What do you think I should search to find that thread? 


Sent from my iPhone using Tapatalk


----------



## Pappy (Jul 29, 2016)

It was down about 6 pages. Pretty much everything you need to know. 
If you need to find it again just keep going through pages until you see a thread with a bunch of pages to it! 

https://forum.tinboats.net/viewtopic.php?f=4&t=23898


----------



## Florida_Native (Jul 30, 2016)

Thanks, pretty interesting and good information to know. 

Got any connections on where to get motor mounts for a good price? I have a short(standard) shaft and the upper mounts are like $94 each. 


Sent from my iPhone using Tapatalk


----------



## Sinkingfast (Jul 30, 2016)

Golly Gee Whizz..Spend $1500.00 on a rebuild. Get the needed parts and get it done. We are here for you to help you get it done. Not to do searches that you can do..How much is a new 4stink anyway...


----------



## turbotodd (Jul 30, 2016)

My personal experience....

Test boat. 2012 war eagle 548LDV. W45 trolling motor on port side of bow. Low deck. Single battery in the back. Tackle box usually in the middle somewhere and a cooler directly in front of the rear seat, usually holding a 10 lb anchor and some rope. At time of testing, no fish or ice were in the cooler. Just me in the boat and I'm 200 lbs. Hull weight 341 lbs + trolling motor, battery, wiring, 2 running lights and gear.

Motor was a 2007 Yamaha 25hp 2 stroke, twin carb. Bone stock. I had bought it with intentions of reselling it. Motor weighed 114 lbs (electric start short shaft manual tilt tiller steer) on my scale. Mounted to the transom with exactly 2" of lift between the motor and transom top. Top speed 28.6 mph is the highest sustained speed I found with the GPS, at 6070 rpm. ~700 RPM idle speed to plane 3.5 seconds. Minimum planing speed 12.9 mph at 4200 RPM. Prop was 9 7/8" diameter, 11 1/4" pitch-brand new OE Yamaha replacement white aluminum 3 blade.

Loaded, drove home (about 2 miles) and pulled the 2 stroke off the boat, and bolted my 4 stroke in the exact same place. 2000 Yamaha 25hp 4 stroke. Weight 138 lbs. Electric start manual tilt short shaft tiller steer. Drove back to the lake, within an hour of the 2 stroke run.

Top sustained speed 28.9 mph at 6110 rpm. 740 RPM idle to planing speed 3.4 seconds. Minimum planing speed right at 13.2 mph at 4210 RPM. The prop was the exact same prop that came off of the 2 stroker. AL 3 x 9 7/8" x 11 1/4". I just pulled the prop off and stuck it on the 4 stroke just to keep everything about equal, to satisfy my own curiousity. I can get out of the hole a lot quicker with a 10" on the 4 stroke but then it is on the rev limiter at 26.5 mph. 

Best I could tell, there wasn't much difference other than the 4 stroke didn't smoke. And it's easier to start, IMO (no choke).

I can't speak for other manufacturers of boats or motors since that's the only real testing I've done to speak of. Have run lots of flat bottom tins with lots of different motors but never put a pen to paper and actually tested those others, only my own. I did do some testing on a 15hp Yamaha 4 stroke on the same war eagle boat and it was a slug to get on plane but still ran 24 mph, which impressed me.

25hp is 25hp, in my opinion. Some manufacturers pay little attention to satisfying the older crowd and just build a good 25, but it may be down on torque or down on HP compared to the same 2 stroke horsepower. Having spoken with engineers for Yamaha, they wanted to try as best they could to keep the 2 stroke and 4 stroke about the same in power and torque output.


----------



## Florida_Native (Aug 1, 2016)

Pretty interesting thanks for the info. 


Sent from my iPhone using Tapatalk


----------



## scoobeb (Aug 4, 2016)

I have a 20hp 2 stroke mercury and i love it,won't get rid of it unless i got what it's worth but that is another story.If i was going to buy a 25hp there isn't anything else i would buy but a 25hp 4 stroke suzuki efi. Best in price,6yr warranty,3 cylinder, and it has some serious balls,lol.It will keep up with any 2stroke if not beat it because i had one and ran one and sold it like a dummy(forced to sell it).I wanted a 2 stroke so bad thinking the same that it was so much better plus money issues,wrong.Do i love my merc,100% due to price i paid for it but if i had to do it all over again i would keep the suzuki forever and i may just get one here if i can sell my merc for what i know it's worth as my money situation is a bit better now to.The suzuki was one of the sweetest outboards i have ever run and the torque was insane and it sipped fuel. i'm a 2 stroke guy buy i'm slowly starting to change the way i feel.The suzuki is lightest in it's class also at only 136lbs.Everyone has there opinion of what's the best but i'm talking for the money hands down the best. I got mine on onlineoutboards for only $3100 but that was with a rebate and i talked the price down also on top of it.Around holiday seasons suzuki runs the rebates so that is the best time to buy,check out the youtube videos for proof of how it runs,it screams and is efi,can't beat that.


----------



## scoobeb (Aug 4, 2016)

By the way it pushed my 1648 flat bottom alumacraft with over 1000lbs weight 32.4mph gps with a 12 pitch prop,that is pretty impressive.It was a flat calm day on the lake to so no wind,etc...Like i said i was a stupid dummy for getting rid of it.I love my merc,but once i sell it,suzuki 25hp all the way.Just imo.


----------



## turbotodd (Aug 5, 2016)

scoobeb said:


> By the way it pushed my 1648 flat bottom alumacraft with over 1000lbs weight 32.4mph gps with a 12 pitch prop,that is pretty impressive.It was a flat calm day on the lake to so no wind,etc...Like i said i was a stupid dummy for getting rid of it.I love my merc,but once i sell it,suzuki 25hp all the way.Just imo.



So, it was running 6600+ RPM? I did not know that they'd run that hard.


----------



## scoobeb (Aug 6, 2016)

I don't know what rpm it was running,all i know is it was doing 32mph,gps by the way.


----------



## scoobeb (Aug 6, 2016)

Have you ever ran one on a flat bottom boat?The 25hp suzuki has insane power,i used a bigger prop so no the rpms would go down not up but i'm sure you knew that already.I had a 20hp 4stroke suzuki and on my 1648 with the same weight i ran close to 28mph with a 11 pitch prop so how would an extra 4mph not be possible in your eyes with a much more powerful outboard???????????????


----------



## Florida_Native (Aug 7, 2016)

That's awesome, so I'm guessing a 1648 is 16' long right? 


Sent from my iPhone using Tapatalk


----------



## scoobeb (Aug 8, 2016)

Yes,16ft.I have had some really great success with outboards being so powerful.I now have a 1993 20hp 2stroke mercury that has insane power also.It runs 30.7mph with just me in the boat with a 13 pitch prop.The 20hp suzuki has incredible power also for it's size and only 97lbs which is impressive but it is a big difference from the 25hp suzuki.I have had both and they both ran i mean like beasts for their size.If you went with a 20hp suzuki you would not be losing to much over the 25hp you have now,maybe a couple mph but think of how much fuel you will save and oil.They both i mean sip gas.


----------



## scoobeb (Aug 8, 2016)

Remember it takes very little to move a flat bottom jon boat so the 20 or 25hp will make it scream.


----------



## turbotodd (Aug 8, 2016)

Most aluminum hulls have a LOT more drag that most people think. The ribs on the bottom are designed to help "stick" it to the water. That said, there are about 4 or 5 (that I know of) manufacturers that build "performance" aluminum hulls, built to handle decent and run faster than most ordinary aluminum boats.


----------



## sunshine (Aug 8, 2016)

Guy here at work went from a 115hp 2 stroke to a brand new 140 hp Suzuki 4 stroke on his 18-20 ft bay boat and lost top end speed (2mph) and hole shot performance. He's still working on propping it, but hasn't had much luck.


----------



## Florida_Native (Aug 8, 2016)

scoobeb said:


> Yes,16ft.I have had some really great success with outboards being so powerful.I now have a 1993 20hp 2stroke mercury that has insane power also.It runs 30.7mph with just me in the boat with a 13 pitch prop.The 20hp suzuki has incredible power also for it's size and only 97lbs which is impressive but it is a big difference from the 25hp suzuki.I have had both and they both ran i mean like beasts for their size.If you went with a 20hp suzuki you would not be losing to much over the 25hp you have now,maybe a couple mph but think of how much fuel you will save and oil.They both i mean sip gas.



Right on, I think I'll end up with the 25hp. Currently I have a 16' Jon boat with a 97 25hp Evinrude and it will push about 30mph. I just want to stay where I'm at, I didn't want to buy a new motor then end up slower. The motor is a champ really, not sure what prop is on there but I'm sure it's dinged up and whatnot. 

Only reason I'm really looking to change is my dad wants a newer 4-stroke to be quieter and less smokey lol. 


Sent from my iPhone using Tapatalk


----------

