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Hot rod 9.9 build up

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BRUPP79

Regular Contributor
I know this has been rehashed to death. But I am starting a 9.9 Johnson hotrod build on my 75 model.. I know the longevity might not be there and all that jazz. But basics will be, basic port polishing, either a exhaust tuner change or just polish the factory square one, Boyesen reeds, bump compression a hair then 93 oct fuel, possible propeller change as well depending on what I'm looking for..
First question on the cyl head. I see there were atleast 3 different heads, other than cover shape and T-stat location, is there a performance difference? Think old SBC SMOG heads vs. heart shape combustion chambers. Second, I know that the exhaust runs out the prop center and one would think that the water would create a suction on the exhaust to help draw it out, has anyone ever monkey'd with that? Meaning mod a prop to create more draw by Venturi effect? I have tried doing some searching and I can find some basics that I've picked up on, but it seems like other than basic parts swapping and Common Sense things everybody is tight-lipped about performance modifications. And I guess with the racing people I see good reason for that.
Just curious what others have done. I'm not looking for profit on this, like taking it and selling the ideas. Just something to do in the garage when it's 20 below zero. Thanks
 
Get the parts off of a 15 up. The short tuner and reed spacers then square up the ports only, Do not polish the intake side of the motor and find a 2 blade prop for it. Leave the exhaust alone to much pull from t prop and it will run lean. Leave the compression alone to as it is a crossflow motor, as is the motor is capable of 6500 rpm. A later motor would be better because there were bearing changes on the crank. Those could spin to 7000 rpm.
 
flyingscott said:
Get the parts off of a 15 up. The short tuner and reed spacers then square up the ports only, Do not polish the intake side of the motor and find a 2 blade prop for it. Leave the exhaust alone to much pull from t prop and it will run lean. Leave the compression alone to as it is a crossflow motor, as is the motor is capable of 6500 rpm. A later motor would be better because there were bearing changes on the crank. Those could spin to 7000 rpm.
Click to expand...

I am searching for a tuner. I thought I was getting a newer short megaphone one off of a newer 15hp, well I did get a tuner from a newer 15hp, happened to be a square one. UGGHH. Ohh well, try again. Call up Tim's. I am guessing you meant "square off only the exhaust ports" leave the intake alone? I assume that, just goin off of what I have scrounged online, square top and bottom of exhaust ports but don't raise or lower them will help it rev up high. I have also read to chamfer the "flow exiting corner" of the ports going with the flow of exhaust? Thoughts?? I dunno.

I read/heard from some local 2 stroke sled tuners is that you sand the rough casting marks on the intake side to about a 80-100 grit finish and that helps keep the fuel charge stratified. Then do the same to the exhaust as far as smooth castings and get rid of spots in the path that hang up the flow, but that you want to bring to near mirror or there abouts?

As far as leaving the squeeze alone, what would the reason be other than I know it is easier on the internals, if I may kindly pry. Seems like most guys will shave .030" off. I have done it to other 2 cycle engines and it has helped. But if is a no-no on an outboard, great! Knowledge is power:cool:

How abouts the heads? Only thing I can find is get the newer one with the easy access T-stat on it. Nothing is mentioned as far as performance, only that it is better. Guessing due to the easy to change the T-stat.

I know alot of time went into this engine from the get go, but there is always things it seems like can be done. Even if you get it to "breathe easier", less congested so to speak, the motor will be more happy.

Prop should be simple enough, load the boat to the approx cargo and get it to rev to the safe limit with the appropriate prop.

Thanks so far for the ideas, any more keep em' coming. I will post my direction and results (well in May I will):cool:
 
Had a 1949 or 1950 Speedifour....I think rated at 33 HP. Had a Big 4 carb and some porting with 4 megaphones out the back. It had been raced on a hydroplane back in the 50's. Never used it but had it running on the workbench for a few seconds. The neighbors almost called the cops.... eventually I get run out of "Perfectsville". Now live in the middle of 80 acres on a dead end road......and no, don't build explosives in my RV. Build rocket motors in the basement, however, ......not much difference. Gonna see if that old 33 is still up at my friend's farm.....talk about a cool old motor. I stored it in a junk car back in the pasture.....hope they didn't scrap it. How about setting up that 15 with a couple expansion chambers? I have the math to figure, engineer and build them. Built one for my old 69 Yamaha DT1.....still have it. That 33 is up in Little Fork......not far from you. I never fixed it cause the crank and bearings were all pitted.....would have launched the rods.
https://youtu.be/eggBytzPPaU
 
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Do not shave head..will not add any compression as crossflow motor. Find a head with smaller internal CC to raise compression. The more you put in the front of motor the more you can get out...needs to look like this....
attachment.php
 
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Hey Tim, had thought of building a external tuner for the motor. One of my old workmates built pipes for FAST Racing in Eveleth, so he has the formulas. But was thinking of keeping this one a sleeper motor. But still would be fun! Someday:cool:

Faztbullet, would you know off hand which head had the smaller cc? I will keep searching on my end also. I have thought of modding a Tillotson HR carb onto this motor to keep it looking somewhat stock. I have one with the external impulse line, so it would be a matter of making the linkage. Not too terrible. Plus I would have the ability to tune the high speed circuit rather easy. I like your twin barrel setup, slick!
 
See if you can fit a 1993 or newer block on there.----A 2.375 bore and 15.6 cubes.-----Bigger displacement = more power.
 
That's what I call voiding the warranty, Pappy. Sweet work. Is that the "big block" 15? Racer....."there's no replacement for displacement". Do you remember what that old Speedifour 33 was?.....that's a few years before my time! Rupp, was that the shop there on Half Moon Lake?
 
Hey Tim, yep that was his first shop that he had. Now he has a shop in the old Armory downtown Eveleth. I think he's still making the blade snowmobiles although not too many of them nowadays. The M10 suspension front and back is still pretty popular though. I think he does every now and then prototype work 4 Arctic Cat Polaris and Yamaha once in awhile skidoo on the newest latest and greatest kind of like problem solving before it hits the market.
 
Ok, just trying to chase down tuners for my build. So go easy :)
First picture, the standard square is what I have.
Square.jpg
Second, the sought after cone style.
Cone.jpg
Third, a shorty style? Superceed's the cone. Anyone ever see one in real life? Is that the cream of the crop so to speak? I see it is still avail on marineengine. Have thought of asking for a picture just to verify, sometime parts book pictures get messed up.
Shorty.jpg

I noticed Mercury 9.9/15 used the cone style if I saw that right?
Thoughts. Thanks again gentlemen. Will report more as I get going.
 
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Shorter tuners are for higher rpm and longer is for low end torque. But you need to use what the engine is built to do. It won't do ya any good to use a tuner designed for 7000 rpm on a motor that is ported and set up to make most of its power around 5000 rpm. Your left with a mota thats doggy on the bottom end or lazy on top end. If you can get the length of the OEM cone style you can cut and flare your square one...just adding a few pieces of aluminum
 
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Thanks for the info Faztbullet, I have a cone style coming from Ebay for 43 bucks to my door. Most of my porting will be looking for ovious this that shouldn't be IE: casting burrs, flash, sharp corners, things like that
 
Ok, so Next on my re-hash list is intakes. From what I have read it makes zero difference, then others say it makes all the world to the engine.

First style I have seen is what my current project 75 engine has. It has flow dividers at the reed area. Seems like a good idea? Did it turn out to be restrictive in the end? I know they didn't line up good at all on mine, I had planned on port matching them.
intake 1.jpg

Second looks like the first, but less the flow diverters at the reed area. Also maybe less restrictive elsewhere. This style is on my 83 9.9 Evinrude Yachtwin.
intake 2.jpg

Lastly, this one looks like the second, but like they coxed more flow out of it? Also I noticed the divider in the carb throat area is far less than the first and second. Then I spotted a balance passage I am guessing?
intake 3.jpg

I have read that some sand the carb diverter to a knife edge. But then after seeing the third style, perhaps I will buy one of that style if that was their latest and greatest.

I have my current intake, reed plate and engine case half lined up and 3 alignment pins drilled and installed so that when I get it ready I don't need to worry if it shifts out of synch. Just looking what your thoughts and again I will keep searching and reading. I hate to re-hash if this was covered before, but I haven't found it with the search tool. User error I guess? :confused::confused::confused::confused::confused:
 
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