Merc 350

[greg82255]

Hello,

Just bought a new boat. 1986 Formula 206 Spider, original Merc 350/alpha one package. Does about 48-50 right now. Besides switching away from the old cleaver prop, I was thinking about doing some quick/easy engine upgrades to give it a little more power. Any suggestions? I was thinking of switching to a high rise intake and switching out the Rochester carb to a Holley 4160 or something similar. Also thinking about changing to 4 inch exhaust risers.

Would that add a noticeable amount of power? If not, is there anything quick and easy that could be done that would?

Thanks for the help.

 

[Alpheus]

Re: Merc 350

You can add more HP by doing those upgrades, but you wont notice it that much. The best HP boost you can get is to upgrade to the above parts (minus 4" exhaust) and get a set of Vortec heads. Thats an easy 25-30 HP heads only.

 

[45Auto]

Re: Merc 350

Figure on gaining about 1 MPH for every 10 HP you add to the engine. How much is 2 or 3 MPH worth to you?

 

[wire2]

Re: Merc 350

An aluminum hi rise intake will help it breathe in, and save 50 lbs.
The Rochester has 7/8 primaries but 2?" secondaries, it's no slouch for power. I doubt you'd notice any difference going to the Holley.

As for 4" risers, an I/O exhaust has many restrictions way smaller than 4", like bottom of Y pipe, outdrive passages, prop.

One of several hop-ups I did was change the stamped steel 1.5:1 rockers to 1.6:1 aluminum roller rockers. It gives less friction, & a higher valve lift but keeps the duration the same. And they're much easier to install than a cam.

 

[greg82255]

Re: Merc 350

The 4" Risers were more so I could put through-hull exhaust with 4" tips.

As for the Vortec heads, I like the idea but I have never pulled a head before. How hard is that going to be? Can I replace the heads with the motor still in the boat? I have heard that you have to machine the block and the heads if you want it to seal correctly.

 

[Aloysius]

Re: Merc 350

vortec heads require a different intake manifold also.

 

[Alpheus]

Re: Merc 350

There is no machining required for Vortec heads install. Yes you have to by a different intake, but you stated above that you were going to buy a new intake anyway.

You do not have to take the engine out of the boat to bolt on new heads.

Like I said that is the best and easiest way to add "noticeable' HP to your engine...

 

[Aloysius]

Re: Merc 350

You can buy new complete vortec heads for $300 bucks each. Sell your existing heads to offset the cost. They are great bolt-on improvement, because they help all through the stock rpm range. The stock silicone ringed intake gaskets are very tempramental..Fel-Pro makes conventional gaskets you can use.