Prop for 4.3l merc I/O 22.2 ff aquasport

[sebas54]

Hi, I need to replace my Propeller But don't know what size I need.  I just bout this boat in the spring and the guy who sold it to me told me, he went through 4 props before finding one which worked well.  

I have all 4 props but the one thats on the boat, I don' tknow what size it is.
 
I go 23 mph at 3900 rpms with my prop now.  

I would like to go faster if possible.  Thanks

[GoneFission]

You want to run 4500-4800 RPMs at full throttle with a 4.3, so whatever you have now is probably over-pitched - you can do better.  Why not just take a prop wrench, pliers, and a screwdriver with you next time and switch the props until you find the one you like?  It's a 5 minute job to change props, and no theory about what SHOULD work will be as accurate as the real thing!    

Hope this helps - good luck!

[sebas54]

Thanks for the repley.   Can you tell me exactly what size would work best for me.  Thank you.

[riverratjr]

Is your boat at WOT,wide open throttle, at 39000 rpm? Your current prop specs should be machine stamped on the prop body;i.e. 13 7/8X21 or 14X19 etc.

[sebas54]

No it's not at WOT at 3900.  The person that I bought the boat from told me not to go above 3900 RPM.  I cant see the stamped specs on the prop that is on the boat but I do have the specs for the other 3 props that weren't efficient.  Should I just replace the prop with the one thats on it already.   thanks

[GoneFission]

Is there a reason you should not go over 3900?  

4.3 engines are designed to run 4500 to 4800 at full throttle; you pobably don't want to run at WOT a lot, but you can't prop the engine if you don't.

See what  she runs at at full throttle.  If she tops out between 4500 and 4800, she's probably propped about right.   :)

[sebas54]

I think the reason he told me not to go above 3900RPM's is becaquse he replaced the engine with a truck engine.  I think?  Would this be the reason he told me this?

[Capt. Bob]

Wow,
This is like herdin' cats

[GoneFission]

Mercruiser and other marine applications use a GM 4.3 block.  Technically, all 4.3s are truck engines.  Here's the history of the 4.3 litre V-6, also called the Vortec 4300:  

It started as a 90° V6 truck engine, replacing the Chevrolet 250 in light trucks and 200/229 90 degree V6s in passenger cars (the 200 and 229 were known as the V6-90, both were shortened versions of the Small Block Chevrolet). It is based on the 350 in³ (5.7 L) Chevrolet small-block V8 with 2 cylinders cut off to make a V6. Note that if you take 350, divide it by 8 and multiply by 6, you get 262 - the displacement of the 4.3 engine.  

The engine first appeared in 1985 with the throttle-body injected LB4 in passenger cars (light trucks and vans had carburetors until 1987). In 1991, the limited-edition GMC Syclone featured a 280 hp and 360 ft·lbf turbocharged/intercooled LB4 with the first use of multi-port fuel injection on a Vortec V6. The central-port injected L35 (Vin 'W') debuted in 1992, with better breathing for 200 hp (150 kW). Another CPI engine, the LF6, joined the rest in 1996, while the LB4 was retired after 1998. In 2002, GM introduced a new multi-port injected LU3 engine, and a LG3 variant appeared soon after. This engines origins date back to 1955, when the original Chevy small-block V-8 was introduced.

All Vortec 4300s use a cast iron block and heads and 101.60 mm (4.000") bore and 88.39 mm (3.48") stroke (bore and stroke dimensions the same as a 350). Connecting rods still measure 5.7" although the rod journal diameter is 2.25". They are OHV engines with two valves per cylinder and are produced in Tonawanda, New York and Romulus, Michigan. Power output of the new LU3/LG3 engines is 180-200 hp (134-150 kW) and 245-260 ft·lbf (332-353 N·m).

So it really does not matter if it's an engine out of a car or a truck - it should still run 4500-4800 at WOT.  Yours probably has a carburetor, but may also have fuel injection - both have been offered for marine applications.  Note that 4.3 engines are 90 degree V6 blocks, and are inherently unbalanced engines compared to a proper 60 degree V6.  Some balancing magic can be done with offset crankshaft journals, but a 90 degree V6 is never going to be a smooth-running engine, especially if over 3 litres displacement.  A properly balanced 60 degree V6 can run 8000 RPM - in fact Mercury V6 outboards (all 60 degree - except for the 3.4 litre) easily run over 6000 RPM.  However, a 4.3 V6 should have good torque characteristics, and the fact that GM has built a couple zillion of them means parts are cheap!  

Hope this helps - see the previous message regarding propping.

[sebas54]

Thanks for all the info, I really appreciate it.  
So, do you think it's ok to go past 3900 rpm's?  I am hesitant because I never went past that.

 The reason I want to change the prop is because rope got tangled around it and it bent the hub in, but the blades seem to look fine.  

Is it ok to drive the boat with the hub bent in?

[aqua70]

Why would you not be able to run at wide open throttle?
We have an  280 OMC with a Chevy 5.0 litre and run at 5200 wide open. (53 mile per hour).Cruising speed (38 to 40 mph)we are at about 4000 to 4200 rpm.
     Just asking!

[sebas54]

I don't know.  

I was told not to go above 3900rpm's and because the engine is from 1988.  If you guy's say it's ok then I will give her a try.

[riverratjr]

[GoneFission]

Let's see, engines, props, and now "I want to change the prop is because rope got tangled around it and it bent the hub in, but the blades seem to look fine."  

Jeesh!     Well now that's a different story (this really IS sounding like herding cats...)   If the outlet of the hub is all that's bent, it's probably OK to run -  BUT - if the main section is bent, the blades will not be balanced and aligned and the prop is definately NOT OK to run.  The vibration is likely to damage the seals and bearings in the lower unit.  

Is there any chance that the previous owner set the 3900 RPM limit based on a damaged propeller and vibration?  That might make sense...   Anyway, how about a picture of the prop and hub?  That might help!

[aqua70]

Hey John, The guy is new and has some questions. Just like I had in the beginning. Your answer and advice was indepth and professional. Lets not try and scare him off the web.