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 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

[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.