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I am putting a 5.7 V-8 in place of a 4.3 V-6 (175 HP rated by Merc)in my baja. I was wondering what the advantages and disadvantages of just putting a different prop on the boat VS regearing the drive to 1.5 : 1(Current ratio is 1.84:1.)and putting a different prop on were? I am running a 14.25 by 21 SS prop now. Either way I need to do something or I will bouce off the rev limiter. I am hopping for about 300 HP when finished rebuilding the 5.7. What kind of speed should I expect? The boat is an Islander 180 and it runs at 49.5mphGPS at 4900 rpm right now.
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Replace the prop. It will be cheaper than regearing. You are still low enough in prop pitch to have an excellent selection.
A couple of facts...
A higher (numerical) gear with a higher pitch prop will accelerate faster than than a lower gear and smaller props. Once you step over 32" in pitch the slip factors get screwy and regearing will be necessary. That's why you don't see many props over 34-36".
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This also applies to me. I have a 1991 SkiPro with a stock MerCruiser 260 (230 propshaft horsepower) Holeshot at my elevation (4500 feet) is lacking. I have a 19" 3 blade stainless prop with 1.5 gears. Max rpm is 4450 rpm. Top speed is 50 mph, verified by radar. Dropping to a 17" wheel seems a little wimpy to me.
I'm thinking that building a 383 stroker may be the best solution. Any suggestions?
[ September 12, 2003, 10:50 AM: Message edited by: Miss Rita ]
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I bet if you went to a four blade 17" Mercury Offshore prop, you would get an awesome holeshot, plus gain mph on top. Who cares what the prop numbers are, it's all about performance.
