Merc 350 Mag Performance Increase Options

[reference123]

I have a Merc 350 mag that is only a couple years old and in great shape. I dont care much about more speed but would love to increase the torque.

I added a K&N flame arrestor with velocity stack which did seem to provide a minor increase (and you can sure hear it sucking the air in).

Are there any other options such as computer adjustments (like chips used in many cars and trucks)? I know those can increase the engine temp but I currently run just over 140 degrees (the manual says it should be 160 degrees).

I considered a pro-charger supercharger but the Bravo 3 drive I have will not handle over 400 HP and the supercharger would bump it up to 450.

 

[WillyBWright]

Re: Merc 350 Mag Performance Increase Options

You'll never blow a Bravo with a smallblock.

If you don't already have it, try thru-transom exhaust. I'd go 3" with a smallblock. You could stroke it to a 6.2L (aslo requires the 6.2 computer), but MerCruiser doesn't make a whole lot of performance stuff for smallblocks. They much prefer to spend their R&D on bigblocks. You don't want to get too carried away with multiport injection models because of the EFI computer. It's pretty specifically programmed. If you had a carbed motor, the sky's the limit. If you want Hi-Perf, swap out the motor with one already made that way.

 

[Almeja]

Re: Merc 350 Mag Performance Increase Options

Looking for more torque? Is the engine bogging and not reaching rpm as you come out of the hole or is the boat simply not coming out quickly enough?

IMHO: Best investment might be a different propeller... a lower pitch, or maybe you could use a 'ventilated' prop.

These props deliberately ventilate (introduce air to the prop) at low speeds, allowing the engine to build revs and get into it's power curve. As the boat acellerates, the ventilation stops and the prop gets full bite.

The amount of hole shot ventilation is adjustable by adding/removing plugs to the ventilation holes.

Think of it as a 'torque converter' for boats.

I think you'd get a lot more bang for the buck with a prop change than pumping up an already torquey engine.

Adding trim tabs are another option you might think about too...

 

[reference123]

Re: Merc 350 Mag Performance Increase Options

Thanks for the advice. With my current pitch (22) I am at the correct WOT range (4800rpm). The boat is great until it is loaded down close to passenger capacity which we do on a regular basis. That is why I am looking for more torque.

I have been considering trim tabs and maybe need to look into those more.

 

[reference123]

Re: Merc 350 Mag Performance Increase Options

I was reading another post about vortec heads. In 2002 did the 350mag come stock with those or would this be a possible option?

 

[Don S]

Re: Merc 350 Mag Performance Increase Options

If you do most of your boating with a full load, do your WOT test fully loaded, and reprop it so you get 4800 rpm with that load. Then when you are lightly loaded, just watch your rpm.
If you want more torque, you need more Cubic Inches.

 

[AdamB]

Re: Merc 350 Mag Performance Increase Options

I wonder if you could get aftermarket intake manifold for your Merc? Something with longer intake runners is supposed to give more torque...

Otherwise, definitely I would go with lower pitch prop (at least when running full load) and smart tabs helped my stern heavy 21' Wellcraft. I also run a 22" prop and now I hardly get any bow rise whatso ever.

 

[reference123]

Re: Merc 350 Mag Performance Increase Options

I am at the 4800 RPM WOT with the full load. Bow rise isnt that much of an issue based on the design of the hull.

Smart Tabs are great, I have them on the other boat and it made a world of difference.

I can supercharge for less than half the cost of repowering the boat. Does anyone that is an expert on the Bravo III agree with the earlier post that it is unlikely I would damage the drive with the increase in torque and horsepower from supercharging?