Prop for my 1981 century 2000 with a 350 swap?

81century2000

Recruit
Joined
Jul 31, 2018
Messages
2
Hello, this will be my first post, I have read many prop threads on this forum but I cant seem to find the exact answer I'm looking for so hopefully someone more knowledgeable about props will pitch their opinion. My boat is a 1981 Century 2000 with a 350 mercruiser engine swap with an edelbrock 4 barrel carb and aluminum intake. Boat runs strong. My boat came with a 305 from the factory. My outdrive is a mercruiser pre-alpha model. Not sure on the gear ratio. The prop currently on the boat is an aluminum 14.5x19 pitch and has minor dings and looks pretty old. WOT specs are 46 mph at 5000-5200 rpm. With 500 pounds in the boat it planes quick and doesnt bog down whatsoever. So I'm trying to get my rpms down to 4600-4800 WOT and a few more mph wouldn't hurt. I want to stick to an aluminum prop unless I can find a good used stainless. Money is tight. So what would be the best pitch for my exact application and where would I find a prop that will fit, with all the necessary hardware, prop finders are vague for my application and I cant find anything for a pre-alpha out-drive. I will be installing the prop myself I am a mechanic. Thanks!!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
welcome aboard

knowing your drive ratio is a good thing.

its not a pre-alpha drive. there is no such thing as a pre-alpha, its either an MC1 or an R . being 1981, it would have came with an MC1, however the boat is coming up on 38 years old so anything is possible, including it being an Alpha

information is in the stickies on drive identification.

here is a link https://forums.iboats.com/forum/eng...utdrives/10596184-what-is-a-‘pre-alpha’-drive

for every 2" in pitch estimate a 400 RPM drop

so shoot for a 21p. you should be able to swing anywhere from a 14-15" diameter prop
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If going for a 21 pitch prop as recommended by Scott post wot results as to know if the 400 wot revs rule of thumb decrease were decreased as stated going + 2 pitches up.

Happy Boating
 
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