OMC airbox mods ???

[bmurray]

I had an engine builder mention to me about some airbox mods for improved performance. I have an 85 Johnson 150 crossflow. I'm in the process of polishing and porting an intake and reed blocks for my engine. Has anyone heard of this and if so what or how is this done? If anyone has any ideas on this, please reply and email me at my work address at bmurray@hydromat.com<br /><br />thanks, Bob

 

[Dhadley]

Re: OMC airbox mods ???

On a crossflow it may be as simple as removing the air box cover. Try it and see what happens. usually it will pick up about 100 rpm at 5800-6000.<br /><br />Porting the intake doesnt seem to do much. Polishing may hurt. What will help tremondusly is to mill out the wall between the intake passages on the carb side of the intake. Now each cylinder can pull from both carb throats. There is a small carb mod that goes with this and you need to get some Aqua Power carb gaskets #959. <br /><br />Good luck!

 

[bmurray]

Re: OMC airbox mods ???

do I get the gaskets from Aqua Power? they have a website? DHadley, glad to hear from you again. As you can see, I'm back at it this season on some mods on that old 150. haven't milled the heads just yet. Are there any drawbacks from connecting the two sides together? Remember I'm trying to gain back some R's(HP). thanks

 

[Dhadley]

Re: OMC airbox mods ???

Any dealer can get them from one of many distributors. I'm sure most any on-line site can supply them if you specify them. <br /><br />Ive never ran into a downside of a plenum manifold. It doesnt require any jetting change (thru 6500) and they idle smooth as silk. From the outside they look stock and pull like crazy.<br /><br />Good luck!

 

[dpminc]

Re: OMC airbox mods ???

Just a thought, but wouldn't adding the "bubble back", and exhaust stuffer blocks from a 175 crossflow help too??

 

[bmurray]

Re: OMC airbox mods ???

what is "buble back and exhaust stuffer blocks"?

 

[bmurray]

Re: OMC airbox mods ???

one more thing. What about some sort of louver for the crowling? I can't see where this engine has a good air flow into it.

 

[OBJ]

Re: OMC airbox mods ???

Dhadley...could I do the same thing to a 90hp 86' Rude? What kind of mod would I need to make to the carbs? <br /><br />bmurray...thanks for the e-mail and sites. Very interesting. Let me throw this at you. I had a 9.9 come in with a neat little mod on it. Guy bored a hole through the side of the hood opposite the carb cover air intake hole. He then used PVC pipe with an elbow pointed forward to ram air into the carb cover air intake. He said he could tell the difference in rpm and speed at WOT.