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**STEVE FRENCH** · 05-23-2011, 02:00 AM

These were built with performance in mind from OMC......I believe Charlie Strang was part of design team with APBA racing in mind when these were built....Not sure you are going to improve much on it and stay reliable as a fish'n motor?...Any formula-A builders out there (I have one, and it mostly just blue-printed with a 1/8" off tuner stack)...Might want ta keep/sell as is and find a 25HP?..........Anyone else have thoughts/sugestions fer dis fell'a?

**Bill Huson** · 05-23-2011, 04:01 AM

105 psi is a tad low. Are you checking compression with the throttle at wide open which is SOP? If it is that low, time to re-ring. Leave the exhaust stack (not a muffler but a tuned exhaust). There's a water pee hole on the bottom of the block that wets down the tuned pipe to cool it. If you plug that hole your engine should pick up about 300 RPM.

**johnsonm50** · 05-23-2011, 04:29 AM

Its not easy to find more power from outboards in things that look restrictive which usually aren't like the tuner. When OMC restricts things its usually a carb insert or smaller size, a restricted intake manifold &-or timing settings. Since you have the bigger of the 9.9/15 you wont find that. Re-ringing should be done, if you mill the head it might accelerate a little better but top end will be about the same. If you mess with ports its hit or miss, might slow it down if wrong. Keeping in mind that its already over a HP per CI its pretty good now. Comparing to motorcycle HP's per CI's wont fly because there's no transmission to spread the power- an outboard needs the torque.
The most you can do will be in prop choice, set up & boat condition [weight & its distribution]. There's always room for improvement but with limits. Good Luck

**aaronmt** · 05-23-2011, 07:53 AM

I checked the psi without the throttle open,cant believe I forgot that with all the motors ive checked.Im not looking for a whole lot more really,just a bit more pop out of the hole would be nice.If I were to shave the head how much is a good place to start?Was there thinner head gaskets available?Will plug the hole that wets down the exhaust make this much louder?What about reads and cleaning up the intake a bit?Keeps the ideas comeing guys I sure appreciate it.Heres a picture of the boat its on its a 10ft livingston,going to a physically larger motor isnt real a option.Dont laugh I need to build teh trailer to fit the boat still so its just sitting on it in the pic.Thanks Aaron

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**johnsonm50** · 05-23-2011, 03:25 PM

Originally posted by aaronmt View Post

I checked the psi without the throttle open,cant believe I forgot that with all the motors ive checked.Im not looking for a whole lot more really,just a bit more pop out of the hole would be nice.If I were to shave the head how much is a good place to start?Was there thinner head gaskets available?Will plug the hole that wets down the exhaust make this much louder?What about reads and cleaning up the intake a bit?Keeps the ideas comeing guys I sure appreciate it.Heres a picture of the boat its on its a 10ft livingston,going to a physically larger motor isnt real a option.Dont laugh I need to build teh trailer to fit the boat still so its just sitting on it in the pic.Thanks Aaron

These motors make real speed as racers with the bolt on gear case & the right year block & parts but would do little good on a standard boat see what the compression is on a retry & look into prop, setup & weight optimizing, without those being good 1st motor work would be that much less effective. Opening up intake passeges isnt always good, 2 strokes rely as much on air velocity as proper volume so that could actually hurt performance. What kind of prop do you have? along with that you'll need to know true RPM's & speed, run weight & gear ratio to guestimate your best choice. Often less pitch will be better & more will kill performance.

**sam** · 05-23-2011, 04:23 PM

I doubt anything can be done to the engine to improve the speed of that rig. Time to save up for a bigger motor.

**smelt farmer** · 05-23-2011, 10:11 PM

raise the motor off the transom an 1 1/2 inch
and go fishin
smelt farmer

**smelt farmer** · 05-23-2011, 10:15 PM

raise the moot off transim an 1 1/2 ich and go fish'n
put watch the first trun
smelt farmer

**Skoontz** · 05-24-2011, 05:57 PM

Another thing you will see with the OMC 15 is that the higher compressioon engines, meaning those on the smaller side of the allowable cc's for the chamber are typically slower than those in the middle of the tolerance, as per Ed Runne, who is one of the APBA inspectors.
Thats not to say if you started stuffing more fuel, maybe alky, and then raising the compression ratio you could see something. Before you start milling a head, take some modeling clay or a soft piece of solder and stick it on top the piston, then torque the ehad and gasket and run it to TDC. Pull out the modeling clay or solder and measure it. You most likely can cut a lot more than .025 off the head.
But seriously, put a nosecomne on your gearcase, raise the motor out of the water, and buy some props before you mess with the powerhead. Your money will go a lot farther.

**Tomtall** · 05-24-2011, 07:23 PM

Another way to check head clearance

Before you start milling a head, take some modeling clay or a soft piece of solder and stick it on top the piston, then torque the ehad and gasket and run it to TDC. Pull out the modeling clay or solder and measure it. You most likely can cut a lot more than .025 off the head.

You can also use parafin wax used for canning.

Melt on stove top in double boiler.

Raise piston to TDC.

Pour hot wax into spark pug hole and let cool.

Remove head and measure clearances.

These motors hit the top corners of the pistons when shaved to much.
Measure twice cut once.

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**Skoontz** · 05-24-2011, 07:46 PM

Cool idear Tom! My granny would be proud to see that the wax she used to cover her home made jellies can be used for something her son, my dad enjoyed...LOLIt's sort of like when I used Arbonne skin creme for needle bearing asmbly grease...The same stuff that can be used to make skin smooth can hold bearings in place....

**aaronmt** · 05-26-2011, 05:55 PM

Ok guys heres the final plan.Im mostly doing this becouse I want to replace most the gaskets on this motor,so mght as well see what I can get out of it.Plan is to block off the water hole that cools the exhaust,basically dry stack it.While im there im gonna smooth the exhaust out as much as I can,not sure what or how much but ill do what I can.I will check to see what I can take of the head and still maintain squish and clearance.I found Boysen reeds for $25,id prefer tdr but at $25 the boysen will do.With the intake off ill also look at what i can clean up in there,basically checking for casting flaws.I will then rough it up(intake should be ruff exhaust smooth).Ive found a 9p prop that will be alot better then my stock 10p.The motor will be rasied roughly 1" to 2" by adding a aluminum spacer so it will stay up.

I know this is in no way a speed boat or performance boat.I just enjoy rigging and setting up boats.Ive had alot of performance boats includeing a 98mph (gps) Allison Grandsport and a slew of other 70-80mph boats.Our current boat that replace the Allison is 22 Velocity O/B with Mercury 250xs,itll run mid 70s.Im no newbe to boats just havent messed with this small of a motor much.Thanks for all the help and Ill tell ya how it all worked out.Aaron

**Tomtall** · 05-26-2011, 07:16 PM

Casting flaws

I found Boysen reeds for $25,id prefer tdr but at $25 the boysen will do.With the intake off ill also look at what i can clean up in there,basically checking for casting flaws.

Just a few notes pics to take what you want to for your build.

If you want to, the reed plate can be dressed to allow more flow for the Boysen reeds. The stock plate resticts the Boysen reed as they have a different shape over the stock reeds. Also the Boysen -R reeds are a thicker reed than the non R boysen reed. (-R prefered)

The reeds are badly restricted on crankcase side. Open this area up. Do not be overly concerned with crankcase volume. It has little affect unless you go way overboard. Fill the stansfer slot on the underside of the block to dry up the exhaust. When doing so try and go with solid mounts as the stock rubber ones will eventually burn out from added heat.

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