4.3 Mercruiser Prop Questions

blorr

Cadet
Joined
Sep 18, 2009
Messages
12
I'm a newbie boat owner and have some questions.

I have a 4.3 Mercruiser with a Alpha One outdrive on a 18ft. Dynasty boat motor and boat are 1993.

Here are my questions:

What should be my top speed? I'm only getting up to 37mph with one person in the boat with it trimmed up. That seems slow.

What is the best prop? Currently I have a Solas 15 X 19 stainless 3 blade. We do ski alot behind it. Is this the best size and pitch?

Right now my max RPM's are barely getting to 4000 with it trimmed up. Is this too low? Does it matter?

I really appreciate your help. Some of these might be dumb questions, if so I apologize.

Thanks for the replies!

Brent
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: 4.3 Mercruiser Questions

Re: 4.3 Mercruiser Questions

Since about 90% of this post is about speed and prop, I am going to move this over to the prop forum.

Sometimes the boat just dies while running at WOT. It takes about 10 minutes to get it started back. Is this a fuel pump issue?

I would suggest you post the above quote as a seperate question in the IO forum.
Asking to many different questions in one post is going to be real hard to follow, and will get you fewer answers.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: 4.3 Mercruiser Prop Questions

Blorr, you should be able to get 4,800 RPM out of that motor and since you are only getting 4,000 RPM you need to first check and see if you have a motor problem, which it appears you do from the other statement you made. After you have your motor right come back and I will be glad to help you find the right prop. We want to make sure that we don't change props and the find out you had the right prop all along but the motor problem caused the loss of RPM.


H
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: 4.3 Mercruiser Prop Questions

You are very welcome Brent.


H
 

blorr

Cadet
Joined
Sep 18, 2009
Messages
12
Re: 4.3 Mercruiser Prop Questions

Let me ask this though.

What should be the typical top end speed at WOT for a 4.3 Mercruiser with a 18 ft boat?

Thanks,
Brent
 

sikz3

Petty Officer 1st Class
Joined
Mar 25, 2006
Messages
244
Re: 4.3 Mercruiser Prop Questions

I'm getting 45 mph (speedo, not gps)@ 4200 with one on board w/ my 18' powered by a 4.3l mercruiser, got more throttle to give but never gave her full hrottle (nervous) bought her less than two months ago and kinda scared to redline her. I have a 14 1/2 x 19p @ 4000' elevation
 

nlain

Commander
Joined
Nov 17, 2005
Messages
2,445
Re: 4.3 Mercruiser Prop Questions

My 04 185 SeaRay, 4.3, Alpha, 14X23 stock prop, with 2 over 200 lb adults, gear for the day, bimini up, 49 GPS, 5200 rpm if tach is right, do not here rev limiter kick in. Max rpm should be 4800. My boat is listed at 2650 lbs dry weight, so loaded I'm a little over 3000 lbs. So once you get your engine checked and right somewhere in the 4800 rpm range and at least mid 40's I would think for your boat, if it is heavier than mine then that will possibly change that a little. Good luck, lets hope just a good tune up or maybe carb rebuild is what you need.
 

truckermatt

Petty Officer 1st Class
Joined
Mar 29, 2009
Messages
384
Re: 4.3 Mercruiser Prop Questions

18.5 foot wellcraft... 44 mph on GPS (47 on speedo) Trimmed up, 2 people full tank of gas. 14.25x21p 3 blade
 

blorr

Cadet
Joined
Sep 18, 2009
Messages
12
Re: 4.3 Mercruiser Prop Questions

Ok, here is what I got.

Had a 15X19 stainless prop and got 4100 RPM at WOT and top speed of 37

Put a 15 3/4 X 15 Stainless mirage plus prop and got 4800 RPM at WOT and top speed of 39.

Definitly liked the second one better because the hole shot was awesome.

This is all with just one person in the boat.

Should I try anything else or is this about what I can expect?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,470
Re: 4.3 Mercruiser Prop Questions

Should I try anything else or is this about what I can expect?

Ayuh,... It sounds like your motor is seriously Down on Power,...
Maybe a Tune Up,+ compression test is in order...
 
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