Re: 3.7/170 Engine upgrades
As far as perfing it out, I don't think much is available. They have big vaporlock problems. If you have the 3" diameter heat exchanger, you'll want to look into a 4". I've also seen later models with fuel coolers very similar (maybe the same) as power steering coolers. Check your bellows for cracks. They last 10 to 20 years. That one's probably about due. I'd also rebuild the water pump. The impeller is rubber and it too ages and should be replaced.
Flush the cooling system and put in fresh coolant. You'd be amazed how many of them still have the original coolant inside. The aluminum block with steel sleeves makes it especially prone to internal corrosion if the coolant's anti-corrosion agents have worn out.
There is an open rubber tube that replaces the exhaust bellows that might give you a tad more Hp, but I'd only use it on a 4-barrel model. Speaking of the 4-barrel, that would be your most effective upgrade. You can go stock or put on a bigger 4-barrel, as long as it's a marine carb.
Retard your max timing by 2 degrees! Burn regular unleaded gas. Avoid alcohol in the fuel as that really aggrivates the vaporlock problem.
Use the blower all the time to help keep the doghouse cool. If you have a 3" blower, put in a 4". Or a second 3" may be even better.
Keep your battery connections clean and very tight. If you blow the voltage regulator, that's over $400. Make certain the connections on the voltage regulator are also clean and tight. They like to corrode. It must also have good clean ground connection to the block.
The alternator magnets in the harmonic balancer like to debond over time. Watch for that. They can be re-epoxied if still intact. Never strike the hb with a hammer. They are very tight to get on and off.
