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Old 11-29-2012, 05:24 AM
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Four winns Liberator


I'm getting ready to install a B&M 144 supercharger on a 211 four winns Liberator that has a 350 sbc 260 hp, any tips? I've been running the supercharger on an old hot rod that I've own for years and decided to de-tune it. need more power for the boat. Any suggestions? Should I or shouldn't I?

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Old 11-29-2012, 05:29 AM
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Depends on what the 350 build is, c.r., cam, heads, exhaust, etc.
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Old 11-29-2012, 10:22 AM
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Also run the projected HP against the factory rating for your outdrive. I know the Mercruiser Alpha One can only take 300hp out of the hole.
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Old 11-29-2012, 05:45 PM
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Use a 750+ cfm carb. make sure the boats fuel system can keep up to the engine demand for fuel at WOT.

Nice blower cam Crane 113801 HMV278
Another nice blower cam Howards #110041
Isky 201271/281-12
summit cam # 1105

In general a cam with 221 to 226 in and 226 to 234 ex @.050" and wider 112-114LSA
works real well for this.
Use suitable hi perf valves springs.
You want a low engine compression ratio 8.5:1 or less.
You do not want to get all greedy with blower boost on pump gas. 4 to 6psi works very well.
You do not want to use low octane gas Use 92+ octane.
you want to use conservative spark advance when under boost on pump gas.
A boost retard box is nice to have. 28 to 32 deg under boost.
User slightly cooler non projected tip spark plugs.
Start with rich carb jetting +6 jets richer pri and sec on a holley.
Use a 10.5" power valve.
If using a marine Qjet on the blower you will need some jets and rods and hangers to tune it.
get the big high flow .149" edelbrock needle seat for Qjet or the GM .135" hi perf needle seat.
Get a fuel pressure gauge.

High boost and agressive timing under boost requires high octane gas.

Home porting your marine motor heads will make more power and really let the blower and blower cam do their stuff.
What is the casting number on your cylinder heads?

You should be able to ad 10 to 12 MPH to the boat top speed....may need a different prop.
You will no save money by using low octane gas on this motor.

if you want to play with high boost, use Hi octane gas and be sure of the carb fuel curve. ( slightly rich under boost is better)
The Mercruiser "Magnum" marine manifolds with the center riser are the best. port matching helps.

The stock Mercruiser "Thunderbolt" ignition box has a built in engine rev limiter.
the V6 Thunder bolt spark box box has a higher rev limit.

Blower motors like a lot of idle spark advance but need a conservative amount of spark advance under full boost , on pump gas.

Make sure the fuel system is marine safe and has enough flow capacity (volume) to feed the blower motor under full power.

When tuning look at all the spark plugs. Watch for detonation and or plug lean mixture and over heat.
Detonation must be avoided.

The amount of boost and sprk timing you can get away with on the street with short full throttle blasts
is no the same as wehat is possible on the water ( extended WOT running)
Watch the Marine marina pump gas. it is usually and often of poor quality- low octane.
use the best high octane pump gas you can. boost 4 to 6psi compression ratio 7.5 to 8.5

Always run the engine compartment purge blower before starting or restarting the engine.
Always start a supercharged motor with the throttle closed.
You should open the engine hatch and run the blower on a restart. Always
Again NEVER start or restart and blower motor with the throttle open. Especially on a boat.
When cold pump the throttle 2 to 3 pumps,,, Close the throttle and start with a closed throttle
When it starts , increase the idle speed to 1500-2000 rpm and warm the engine with the hatch open.
Always watch for fuel leaks. Never allow gas fumes to build up in the engine compartment.

the Alfa Drive will handle a lot more power than it is rated for. Unless its wounded or old age.
What kills the Alpha Drive is not added horsepower . its excessive RPM+ extended time. short WOT drag blasts above 6000 are fine.
You can "cruise " just fine at 5200-5700rpm and get a long long service life from this Alpha Drive with this supercharged 350.
Of course just like a cars transmission and rear axle, if its old , wounded, worn out already....... Your mileage may vary...

Last edited by F-BIRD'88; 11-29-2012 at 06:13 PM.
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Old 11-29-2012, 06:19 PM
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If you build around this proven supercharged engine formula with the 144 blower on your boat,, maximum Horsepower output and max boat top speed will occur at around 5200 to 5700rpm. A radar gun and a few different pitch props to try will get you dialed in. You can go real fast with full reliability on the water with 4 to 6psi boost, decent gasoline and proper carb jetting and timing. A 850cfm carb is not too big at all on this motor. A 600-650 is too small.
A 750cfm or 800cfm edelbrock carb can work very well too. But not all carb models are Marine certified.
A engine compartment fire-explosion is a real bummer in a boat. Make the whole fuel system Marine safe.

The home ported heads and blower friendly camshaft allows this simple supercharged 350 engine to perform at its best all while using very reasonable reliable moderate blower boost.

Last edited by F-BIRD'88; 11-29-2012 at 06:33 PM.
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