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-   -   Increasing horsepower (http://www.wakeworld.com/forum/showthread.php?t=793487)

Bakes 05-21-2012 3:57 PM

Increasing horsepower
So I have ~550 hours on my engine (1998 mercruiser 350 MPI) I am hoping to get another 1000+ hours out of it. That being said, if for some reason it dies, what is the best way to get more power out of it on the rebuild/replacement? Not looking to swap out for a completely new motor; rather, looking for things like new heads, increase the bore, etc. Don't want a supercharger. Just looking to boost performance without sacrificing reliability, 87 octane gas or the pain/hassle of a new engine type.



mhunter 05-21-2012 5:30 PM

Fix the problem with it dieing . Try a different prop

Bakes 05-21-2012 5:54 PM

Sorry....not clear. Engine runs great. Never dies. Has a really nice acme prop. Just looking for options if it ever does blow. Would rather think about it and research it now rather than just take the first thing the tech offers me when I am desperate for a motor


rallyart 05-21-2012 6:56 PM

You increase horsepower by increasing air flow. If you rebuild your engine to run more RPM you can increase the air your can burn so you can increase your power. Then you change your prop or transmission to take advantage of that airflow. It's not that hard to build a 600 hp small block but to get that much power you would have to change the transmission for sure, and put on a high grade performance marine exhaust. 400 hp would not require that much change. Small changes to porting and intake flow or cam will produce some positive results but nothing huge.
Now, a big nitrous kit will get you out of the hole loaded without a problem but it's a pain having to deal with nitrous as a regular thing.

Bakes 05-21-2012 7:48 PM

I'm not looking for airflow tweaks, nitrous, superchargers, turbos, etc. Way to unreliable for what I want to use it for. Just looking for a reliable upgrade path if/when the time comes. It would kill me to spend $3-5K on the same slightly underpowered engine and then find out for $4-6K I could have gotten another 60-100HP.

Anyways, just looked online and saw where you can get a 383 Smallblock with 360 hp for about $3K. That is more what I am looking for.

That being said, what else would I need to replace, change, etc. to convert a 1998 Mercruiser 350 Mag MPI with supposedly 300hp to a 360hp stroker? Can I use the same electronics, etc? Anyone ever done this? Still want reliability and 87 octane gas

05-21-2012 8:16 PM

You might be able to get away with the same electronics if you make a stroker out of it. Granted the ecm will probably have to reflashed with a new custom tune. On the setup you have now there is nothing reading exhaust gases. All it reads is from the knock sensor to advance and retard the timing. You would be running extremely lean with the fuel injection as well if you were to step up displacement. This all being said, its not impossible, you will just have to have someone tune it.

mikeski 05-21-2012 11:09 PM

2 Attachment(s)
Replace the stock exhaust manifolds with Eddie Marine or Revolution Marine manifolds and add O2 sensors. Then find a good programmer to reprogram the MEFI controller to run in closed loop mode versus open loop mode. The offshore guys understand this motor and can probably help you even though your tuning criteria will be somewhat different.

Here are a few pics of my upgrade exhausts.

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