where do I start??

[markt111]

I'm fairly new to outboards, I have everything running good now and I'm starting to get familiar with these animals. I have twin 1994 250 HP Johnson V8 Ocean pro's on a 30' center console, not a 80,90 or 100 MPH boat but low 60's GPS in any conditions, I would like to see a couple more MPH on the high end, have what I believe are the right all around props for my use on the boat now (Mirage plus) I will send them out after the summer for a little tweaking. What can be done to this motor before pulling the heads to raise compression? and how much will it help? would removing the airbox(style with screening in it) help, what about exhaust mods? are they worth it or just louder? I have researched a lot of old post and there wasn't much talk on V8s and what I saw wasn't specific, any input greatly appreciated

[Kim Hanson]

Originally posted by markt111
I'm fairly new to outboards, I have everything running good now and I'm starting to get familiar with these animals. I have twin 1994 250 HP Johnson V8 Ocean pro's on a 30' center console, not a 80,90 or 100 MPH boat but low 60's GPS in any conditions, I would like to see a couple more MPH on the high end, have what I believe are the right all around props for my use on the boat now (Mirage plus) I will send them out after the summer for a little tweaking. What can be done to this motor before pulling the heads to raise compression? and how much will it help? would removing the airbox(style with screening in it) help, what about exhaust mods? are they worth it or just louder? I have researched a lot of old post and there wasn't much talk on V8s and what I saw wasn't specific, any input greatly appreciated
I hate to see nothing said to you, what size props are you running ? 60 seems alittle slow to me with 2 engines! 26 - 32 are good size speed props and the exhaust relieve, don't really know what hp gain...but it sure sounds cool!( Open header car sounds the same ):D :cool: ........( . )( . ).....

[markt111]

the speed I'm getting out of it is what is expected, the boat sits about 6000 lb with a descent amount of fuel in the water, it is a Scarab 302 center console, not a racing type hull, just want to get a little more out of it, where's the best place to pick up the exhaust relief kit or is it a do it yourself mod??

[HavasuDreamin']

I am not real knowledgeable on the OMC engines, but with O/B's in general, I believe the most reliable and easy way to increase HP is through opening up the exhaust.
I would call John's Custom Marine, or write O/B tech in ***boat, or wait for Racer to respond as to the modifications. All three are Alan Stoker. He is the man when it comes to OMC's.
HD

[Havasu Larry]

To cut your heads is a fast, less $$ and a easy way to increase your HP. You can run about 140-145 lbs of compression and still run pump gas. Each engine is a little different so check with someone who knows the OMCs. If you want to really get into it, then rip her down and get the ports modified. They will raise and lower the intake and exhaust ports and open them up. Lots of things they can do its just how much do you want to spend!! Sometimes its less money to sell your engine and buy a bigger one. Well there is my 2 cents worth. Larry :argue:

[Tom Brown]

That's a heavy boat. Basically 3000 lbs per engine. You may not be able to adjust the porting much.
It seems to me that if you want more power, one of the easier ways is to rev the engines higher. That would imply lower pitched props and probably engine mods to allow the engine to live at higher RPM if you plan to go beyond 6K.
I'd find someone familiar with the OMC V8 and see what they have to say. In other words, disregard my post. :D

[markt111]

thanks for the replies, I will have to call Aalan Stoker again I spoke to him regarding basic mods and he said that the exhaust mods/reeds/airbox etc... don't really help just noise makers, I will have to talk to him regarding having the heads/port work done after the season is done here, hopefully he will do this type of work as some people I talk to say leave it alone if it runs good, all the OMC people in my area just want to do normal repair type work