1992 15hp Johnson perfromance hop up ???

[aaronmt]

Tom L. Thanks for the pics,exactly what I was looking for.On the intake pic does removeing the divider effect the bottom end much if any.You have any idea what a safe amouth to take from the head would be without doin the clay or wax.Im not needing it to be on the ragged edge,just about 1 step from it.The pics are exactly what I needed if you have any more ideas what to do im all ears.I did not know there wee 2 different boysen reads,where do you recommed getting the right ones.Thank you for you help.Aaron

[Dave M]

Another Tip

I think someone mentioned this already, but changing the length of the tuner pipe will make a noticable difference. This is not legal in the race engines. But for your project it might be worth trying. Tom may be able to provide the pictures for changing the lengths and what each length change nets you.

[aaronmt]

I think someone mentioned this already, but changing the length of the tuner pipe will make a noticable difference. This is not legal in the race engines. But for your project it might be worth trying. Tom may be able to provide the pictures for changing the lengths and what each length change nets you.

Ya id like to know what is the optimal length while retaing some torque.Im all ears guys.Thanks Aaron

[Skoontz]

I may have missed something so please forgive me...It is my understanding that you are running the stock f-n-r-, thru hub exhaust gearcase, yes? If that is so, you might want to rethink blocking the bypass hole on the block. This is used so that water gets dumped onto the tuner, but, also cools the wate rpump, which is in the top of the gearcase. The reason you can get away with it on a A class racing engine is the direct drive racing engine has its water pump at the nose of the gearcase and the heat of the exhaust does not effect it.

[Tomtall]

More input

Ok a notes regarding your questions.

1. The Boysen 122R reeds can be directly purchased from Boysen at their
web site @ http://www.boyesen.com/
These don't nec. give you anymore speed/RPM but do save the engine
if you suck a reed.

2. Because you are running the stock gearcase you will only be able to raise the engine so high before your water intake starts to suck air and affect your cooling. Also your stock prop will start to cavitate and slip causing reduced speed. I have found that in most cases you can go 1'' - 1 1/2" above stock before this starts to happen. However this depends on how much set back off the transom you have from the bottom of the boat. The further back the engine on the hull the higher you can jack the engine up. There are remote setback brackets that you can purchase for these smaller engines that will work for that purpose. I have used them on applications such as yours with good results. I did however run the "Solas" stainless props when doing so.

3. The cylinder head can usally be milled down to where the step at the head gasket surface is just gone. This will usally give you about 25cc cumbustion chamber volume and still not hit the piston with a stock .050" stock head gasket. See attached pictures.

4. You should have no ill affect taking the devider out of the intake unless if your plan on trolling with the engine. (which you know you are not going to do).

5. Due to you not running a lot of RPM's like a race engine you should leave the tunner pipe at its stock lenghth. Shortening it will only move the peak H.P. to a higher RPM range which you don't want with this engine. You still want to maintain as wide a power band as possible.

6. The dry tuner should not have an ill affect on your water pump as it is contained in a seperate cavity in the midsection with the driveshaft on this engine. The water going thru the pump keeps it cool enough to keep it from melting. You can run a bead of RTV across the divider web on the gear foot between the exhaust cavity and drive shaft cavity to further isolate it from exhaust gas entering that chamber.

Hope this helps. It's fun playing around and seeing what the results can be. Just don't expect a ton of gain here as you are dealing with some restriction in hull and prop limitations. Still fun to experiment however.