4.3L horsepower

[rickminotnd]

I just bought a 2004 Larson 17.5' bowrider. It has a Mercruiser 4.3 LIter, Serial number 0M693427, with Thunderbolt V Ignition. Drive is Alpha One, Gen II (I think, sticker label is pretty rubbed), serial number 0M491238. This boat needs a new prop. I guess I need to know the horsepower to figure out what prop to get.

Actually the ultimate question is what prop should I be looking for. This will be a pleasure boat. There will be a little pulling of a pretty big tube, but mostly just puttering around on summer afternoons. Suggestions on size, pitch and number of blades would be appreciated from you guys. I've reviewed some of your other posts trying to figure this out and it seems like there is a whole lot of knowledge here.

 

[alldodge]

Welcome
Have you removed the prop and looked at the hub?

 

[rickminotnd]

No, I have not yet. It is pretty chewed up and I don't know if the one on the boat is proper. I will take a look and see what it is tonight.

 

[rickminotnd]

Is there something specific you want me to look for?

 

[alldodge]

Looking for numbers as in this pic

 

[Renken2000Classic]

Don't know what an '04 has, but my '86/88 Cobra 2bbl's supposed to have about 175HP. The stock prop (spec, at least) is a 14 1/2 x 19 3-blade, and it works great on my 19.5' boat.

 

[Lou C]

2bb carb was 175 hp, 4bbl carb was 205, my '88 FW H-200 (20'9") was specified from FW to use a 15x17 prop, for more hole shot you could drop the pitch down to 15, although that limits top speed.
The goal is to get your wide open throttle maximum RPM where it should be according to the manufacturer, in my case it is 4600-4800 rpm. If checking this with just one person abord, I'd shoot for the upper end, to allow for the boat being loaded.
The 4.3 in a light 17' boat like that, might be able to pull a 21" pitch or greater to reach the specified RPM, this is an important point because if it doesn't reach that rpm, it causes the engine to labor every time it pulls the boat up on plane, which increases engine wear via overheating combustion chambers and overheating exhaust valves.

 

[Scott06]

Don't know what an '04 has, but my '86/88 Cobra 2bbl's supposed to have about 175HP. The stock prop (spec, at least) is a 14 1/2 x 19 3-blade, and it works great on my 19.5' boat.

your 2004 with a 2 bbl carb is 190 hp at the prop, the MPI was 220 hp

 

[Scott06]

I just bought a 2004 Larson 17.5' bowrider. It has a Mercruiser 4.3 LIter, Serial number 0M693427, with Thunderbolt V Ignition. Drive is Alpha One, Gen II (I think, sticker label is pretty rubbed), serial number 0M491238. This boat needs a new prop. I guess I need to know the horsepower to figure out what prop to get.

Actually the ultimate question is what prop should I be looking for. This will be a pleasure boat. There will be a little pulling of a pretty big tube, but mostly just puttering around on summer afternoons. Suggestions on size, pitch and number of blades would be appreciated from you guys. I've reviewed some of your other posts trying to figure this out and it seems like there is a whole lot of knowledge here.

with a 2 bbl carb the 4.3 is rate at 190 HP at the prop, MPI s are 220 hp.

As AD lays out see what is on there now or have it repaired get WOT rpm readings before tweaking pitch. if the boat is new to you spend some time seeing how it performs before trying different designs and pitches

 

[ScottinAZ]

2bb carb was 175 hp, 4bbl carb was 205, my '88 FW H-200 (20'9") was specified from FW to use a 15x17 prop, for more hole shot you could drop the pitch down to 15, although that limits top speed.
The goal is to get your wide open throttle maximum RPM where it should be according to the manufacturer, in my case it is 4600-4800 rpm. If checking this with just one person abord, I'd shoot for the upper end, to allow for the boat being loaded.
The 4.3 in a light 17' boat like that, might be able to pull a 21" pitch or greater to reach the specified RPM, this is an important point because if it doesn't reach that rpm, it causes the engine to labor every time it pulls the boat up on plane, which increases engine wear via overheating combustion chambers and overheating exhaust valves.

my 17' Four Winns with the 4.3 runs a 21 pitch prop from the factory.