Mercury 15 HP race motor

[Spectre22]

so a couple buddies and i all have jon boats and but im building a little motor to beat them. its a 2002 merc 15hp (2 stroke) anyone ever messed with one of these or has any experience making some more power out of them??

[home made tunnel]

Any two stroke - Machine some material off the head for some more compression - advance the ignition timing some - and look at increasing porting. Also some 2 stroke tricks are "Stuffing" the intake. basically any area or space in the crank case that isn't in the way of the spinning assembly, stuff with JB weld, and smooth it out. The less open space for air to squish in the crank case, the worse it is to transfer air from case, up to cylinder on the down-stroke.

For a 15hp motor though, I don't think your gains will be worth the efforts. If you don't get it right, that's a LOT of rope-pulling to get her started, and tuned in right.
You loose a lot of idle reliability when you really start messing with top-end power.

[nitro_rat]

add a 9.9 cowl, instant 5.1 horsepower...

[FMP]

Find a 1999 Force , Mercury Lightning 25hp triple. 15" 98lbs and put some 15 hp stickers on it. 6500rpm motor
https://m.youtube.com/watch?v=5yX7FEFU2Xs

[capnzee]

Build yourself a beautiful little 12 foot plywood flat bottom boat being very careful to keep the bottom flat and the weight down. Equip the engine very carefully with a good S/S (if you can find one) prop and adjust the engine up on the transom making certain you are still pumping water. If you personally don't out weigh the s--t out of your buddies, you will kick ass. Don't screw up a nice running little 15 HP, Changing cowlings never made any one proud. A great winter project for under a few hundred bucks. The little 15 HP OMC has always been a consistant good runner over the years and there are a ton of them around. Should get you into the 40's. Another option is the 1950-51 Mercury Super Hurricane 10 engine. Search the junk piles. Probably the biggest "head turner" in the history of outboarding. Rod

[Capt.Insane-o]

Not a whole bunch can be done to the 15, plug the exhaust relief holes and work on the front half..the path to #2 is horrible.

[SS Minnow]

Nitrous Oxide System

[Spectre22]

Any two stroke - Machine some material off the head for some more compression - advance the ignition timing some - and look at increasing porting. Also some 2 stroke tricks are "Stuffing" the intake. basically any area or space in the crank case that isn't in the way of the spinning assembly, stuff with JB weld, and smooth it out. The less open space for air to squish in the crank case, the worse it is to transfer air from case, up to cylinder on the down-stroke.

For a 15hp motor though, I don't think your gains will be worth the efforts. If you don't get it right, that's a LOT of rope-pulling to get her started, and tuned in right.
You loose a lot of idle reliability when you really start messing with top-end power.

ok so far I did some mild porting to the exhaust ports, tear dropping them, polishing and opened them up a bit. On the front case a evened put all the rough casting edges and then sand blasted it. I’ll be filling in some parts of the intake with Tank JB Weld once I build the power head. I can’t shave the head because on these small motors the block and head are one piece. I got an electric starter for it so I’m not worried about doing a lota rope pulling (work smart not harder lol). I’ll keep you updated on what else I’ll be doing

[Spectre22]

I already got a 12 foot aluminum v hull because I do plan on going fishing with the guys as well as beating them :D so I’m aiming for 30-35mph

[Spectre22]

Not a whole bunch can be done to the 15, plug the exhaust relief holes and work on the front half..the path to #2 is horrible.
I as well welded the hole that dumps water into the tuner. I did some reading and it’s illegal to do it in the apba j class so it must make a noticeable difference. I’m also going to open some relief holes in the mid.

[FMP]

What's the reed cage like, can you find better reeds. How about the carb, would the old 18 or 20/25 bolt up with mods? Post a pic of the ports and front if you can.

[JrCRXHF]

Buy a OMC 15 LOL


:leaving:

[Spectre22]

What's the reed cage like, can you find better reeds. How about the carb, would the old 18 or 20/25 bolt up with mods? Post a pic of the ports and front if you can.
I have a aluminum reed cage and a plastic/rubber one. I’m most likely going to go with the plastic one. I also have a set of Boyson Reeds and yes due to all the porting I need a bigger carb. The 20-25hp carbs look like their the same housing size and the carb rebuild kits say 6-25hp so I’m assuming it would bolt on. Now the problem is finding one their kinda hard to find...

[home made tunnel]

Looks like you're on your way to get er' rippin.
Post some pictures of your internal work, you'll get more traffic on the post, and more input.

[FMP]

A 15 Force will walk a 15 OMC LOL both low hrs mid late 90s , proper tune , same boat.

[SS Minnow]

A 15 Force will walk a 15 OMC LOL both low hrs mid late 90s , proper tune , same boat.

Yeah, those Force motors were just known for settin the water on fire. Wonder why they went away???

[FMP]

Mostly dummies that didn't look after them with proper tuning.
It's true, I'm not the only one who has seen the Force.

[Spectre22]

429728429730429731429732429733429734429735 the first couple pictures are the rough grinding from grinding out the edges. the rest of the pictures are of it case after i sand blasted it. im going to try to get some pictures of the exhaust work. but i just wanted to get these up first

[Spectre22]

429741429737429740429738429742https://www.screamandfly.com/attachment.php?attachmentid=429739&stc=1&thumb=1&d=1548897428 what ive done on the exhaust side i still wanna even out some edges but its pretty much there.

[Spectre22]

Im also going to need a big carb for this motor so if anyone has a 20hp or 25hp please send me a PM!!!

[FMP]

Am I see things or does the bottom cylinder have a third downward facing port towards the tuner?

The view from the passage up , the right side semi circle corner. If you could use some high temp aluminum ceramic or weld fill it and grind smooth the curve. And the left side top edge, round the fall off nicely. With the cover on that last corner which forms on the bottom floor before the fall off towards the tuner. Does the cover have a shape to round that 90°. If it doesn't I'd try to make something work there so that S turn through to the tuner is more uniform and smooth.

[Spectre22]

No lol it’s the angle I took the picture. the port kinda wraps around cylinder so it looks like it goes downwards.

[Spectre22]

Also does anyone know where i can get props for this motor. ive seen cleaver looking props but can find any for a 15hp (8 spline)??

[Capt.Insane-o]

Powertec and solas

[Spectre22]

430721430722 cleaned up the exhaust work a bit. evened out some of the edges and opened up the bend into the tuner a bit on the curves in the corners. this was only with the carbide burr, i still gotta sand and polish.

[Rmz_boi]

I’m just wondering what sort of results did you get? Rpm and power wise?

[25two.stroke]

Carbs from 6hp to 25 were IDENTICAL except for the bore size and the jetting. I would not go up to a 25 hp carb on that 15 right away. That is likely going to bog as that small displacmtent probably won't make enough vacuum even with the mods you did. I would get an early 18hp carb for one and change the linkage to work from the early to the later. Then get the jetting for that figured out and make sure the motor can pull fuel right. If you have any questions feel free to pm me or call me, I did that stuff a lot a while ago.

The exhaust pipe isn't tuned on those motors either, so some modifications there can yield quite a bit.

[Rmz_boi]

Carbs from 6hp to 25 were IDENTICAL except for the bore size and the jetting. I would not go up to a 25 hp carb on that 15 right away. That is likely going to bog as that small displacmtent probably won't make enough vacuum even with the mods you did. I would get an early 18hp carb for one and change the linkage to work from the early to the later. Then get the jetting for that figured out and make sure the motor can pull fuel right. If you have any questions feel free to pm me or call me, I did that stuff a lot a while ago.

The exhaust pipe isn't tuned on those motors either, so some modifications there can yield quite a bit.

Youll be suprised, I’m currently running a 34pwk on my merc 15 (same model as his) and I’ve had it running pretty well, it needs a lot of tuning still but once I have ported it it will run even better. Do you have any information on porting these motors?

[redbeard_1911]

Carbs from 6hp to 25 were IDENTICAL except for the bore size and the jetting. I would not go up to a 25 hp carb on that 15 right away. That is likely going to bog as that small displacmtent probably won't make enough vacuum even with the mods you did. I would get an early 18hp carb for one and change the linkage to work from the early to the later. Then get the jetting for that figured out and make sure the motor can pull fuel right. If you have any questions feel free to pm me or call me, I did that stuff a lot a while ago.

The exhaust pipe isn't tuned on those motors either, so some modifications there can yield quite a bit.



what would be the best mod to the exhaust pipe to get the most power out of it? we've got a river that's 10hp limit. i'm building a sleeper 9.9 merc. got everything to make it a 15, but i'm gonna try and squeeze all i can out of it.

[rossi]

Buy a OMC 15 LOL


:leaving:

True - I have both an 87 Merc 15 and an 87 Evinrude 15 that I use on a 14' Mirrocraft Deep Fisherman and the OMC is not only faster but has more torque. The Merc even has quite a bit less hrs to boot.

[staylor]

True - I have both an 87 Merc 15 and an 87 Evinrude 15 that I use on a 14' Mirrocraft Deep Fisherman and the OMC is not only faster but has more torque. The Merc even has quite a bit less hrs to boot.

I had the same experience with my old 15 Evinrude- circa 1981- compared to my later model 15 Merc- the OMC ran a good 3 mph faster on a 14 ft open Starcraft fishing boat- plus is was a few pounds lighter and much easier to carry around.
Doug

[redbeard_1911]

430721430722 cleaned up the exhaust work a bit. evened out some of the edges and opened up the bend into the tuner a bit on the curves in the corners. this was only with the carbide burr, i still gotta sand and polish.


did anyone ever find out if this was worth the effort

[Rmz_boi]

I’ve since ported my 15 merc, had it running but haven’t had it in the water yet, just pulled the port a bit wider and added 6° of exhast timing. 3D printed carb adapter for a 34mm PWK carb and advanced the ignition timing.

[Rmz_boi]

518895518896