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PostPosted: 28 Jul 2016, 12:28 

Joined: 20 Jul 2016, 10:51
Posts: 36
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


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PostPosted: 28 Jul 2016, 13:01 
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Joined: 12 Dec 2014, 14:32
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Location: Eastern Mass
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.



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PostPosted: 28 Jul 2016, 13:55 
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Joined: 15 Mar 2014, 16:57
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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.



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PostPosted: 28 Jul 2016, 16:33 

Joined: 20 Jul 2016, 10:51
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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.


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PostPosted: 28 Jul 2016, 18:09 
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Joined: 15 May 2010, 00:38
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Location: Central Florida
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.


Last edited by Pappy on 29 Jul 2016, 09:37, edited 2 times in total.

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PostPosted: 29 Jul 2016, 09:30 
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Florida_Native wrote:
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!



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PostPosted: 29 Jul 2016, 09:33 
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Location: Central Florida
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.


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PostPosted: 29 Jul 2016, 09:47 

Joined: 20 Jul 2016, 10:51
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Pappy wrote:
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?


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PostPosted: 29 Jul 2016, 17:51 
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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!

viewtopic.php?f=4&t=23898


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PostPosted: 30 Jul 2016, 12:14 

Joined: 20 Jul 2016, 10:51
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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.


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PostPosted: 30 Jul 2016, 13:31 

Joined: 05 Oct 2014, 13:19
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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...



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PostPosted: 30 Jul 2016, 20:40 

Joined: 24 Dec 2011, 22:06
Posts: 963
Location: 72032
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.


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PostPosted: 01 Aug 2016, 10:41 

Joined: 20 Jul 2016, 10:51
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Pretty interesting thanks for the info.


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PostPosted: 04 Aug 2016, 01:04 

Joined: 29 Aug 2011, 04:59
Posts: 875
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.


Last edited by scoobeb on 04 Aug 2016, 01:17, edited 2 times in total.

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PostPosted: 04 Aug 2016, 01:12 

Joined: 29 Aug 2011, 04:59
Posts: 875
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.


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