3.0 to 4.3 Questions

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38special

Petty Officer 2nd Class
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Mar 9, 2010
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129
Will a 4.3 bolt up in place of my 3.0 mercruiser? What is the H.P. of the 4.3 and will it have plenty of power to pull 2 adults skier's. My boat is a 17 foot tri hull. I took the cap off today to rebuild the transom.
 
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38special

Petty Officer 2nd Class
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Mar 9, 2010
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Re: 3.0 to 4.3 Questions

My out drive is a 1978 pre alpha if it makes any differance.
 
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robjen1019

Petty Officer 1st Class
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Apr 18, 2007
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Re: 3.0 to 4.3 Questions

the mounts are different and so are the gears in the outdrives. It is doable, but much easier, and usually cheaper to sell boat and buy another with motor you want
 
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boat127

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Re: 3.0 to 4.3 Questions

also you need a y pipe and the strings for the side mounts for the 4.3 where as te 3.0litre had the front mount
 
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38special

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Re: 3.0 to 4.3 Questions

boat127 said:
also you need a y pipe and the strings for the side mounts for the 4.3 where as te 3.0litre had the front mount
Click to expand...

I am getting ready to put new stringers in as well as new transom. Will the 4.3 use the same bell housing as my 1978 3.0 mercruiser and will the 4.3 lend it's self better to performance up grades? Are any of the verious years of 4.3s considered better than others. Thanks.
 
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38special

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Re: 3.0 to 4.3 Questions

robjen1019 said:
the mounts are different and so are the gears in the outdrives. It is doable, but much easier, and usually cheaper to sell boat and buy another with motor you want
Click to expand...

I'm pretty sure i'm done with my boat buying. This is my first and now i know what to look for if i ever do again. Lol
 
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38special

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Re: 3.0 to 4.3 Questions

What kind of MPH could i expect from a strong running 4.3 in a 17' tri-hull?
 
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btoler4th

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Aug 30, 2009
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Re: 3.0 to 4.3 Questions

I have just done a swap from a 4.3 to a 406 sbc,with a yamaha stern drive and I am not even seeing 50mph(speedo is broken though...:cool:. I do need a different prop, which will help, however, the gear ratio in her isn't doing me any favors. I would imagine, you are going to have similar problems, amongst many more, like parts, and their compatability. It has taken my friend and I two years this fall to finally get it on the water. Everyone said it couldnt be done. That just made us dig deeper. I'd say to you my friend, do whatever makes you happy, and find a way. Same time, don't get in to deep. I dont know how in the world we lucked out. Good luck!

If you follow what everyone else is doing, you'll never get 1st place.
 
Bayliner175xt

Bayliner175xt

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Mar 20, 2010
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Re: 3.0 to 4.3 Questions

Howdi... I looked into this and found it to expensive.
Also check your insurance, mine wouldn't cover boat also Transom may need and upgrade apart from all the other little things.

Give idea away. Buy a new boat!!!!!!!
 
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tschmidty

Chief Petty Officer
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Mar 24, 2010
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Re: 3.0 to 4.3 Questions

Yeah, it does not make a lot of sense, you really can buy a better suited boat for what you will put into making that switch.

A 4.3 is not really a great engine for trying to get two adult skiers up anyway. Nor is a 17 foot trihull. For that matter why do you really want to get two skiers up at the same time?

Stick with the 3.0, have fun with one skier, sell down the road and get more suited boat.
 
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Cptkid570

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Oct 18, 2005
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Re: 3.0 to 4.3 Questions

This doesn't answer your question, but what pitch prop are you using? Maybe a prop change for skiing could get you your pulling performance while skiing, and then use a different prop for cruising/speed. It's a lot easier and cheaper than swapping engines.

Anyway, to swap, you'll need to buld the stringers for the 4.3, get a new outdrive that is geared for the 4.3, get a y-pipe for the 4.3's exhaust, get exhaust system for the 4.3, and then of course the 4.3 complete engine.

If you do this, you'd be better off buying a donor boat (cheap boat) that has the entire 4.3 package... and, to be honest, if you do that, you may like the donor boat better than yours.. especially if your's needs a complete overhaul anyway.
 
Howard Sterndrive

Howard Sterndrive

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Re: 3.0 to 4.3 Questions

38special said:
I'm pretty sure i'm done with my boat buying.
Click to expand...
the only way to do the 4.3 swap would be to buy a complete donor boat

people have listed about $4000 of little parts that you would need. exhaust, mounts, outdrive....

even buying used stuff it would be tedious

look how your 3.0 shifts.... how you going to get that valve cover onto a 4.3?

i.e. you need everything including power steering
 
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38special

Petty Officer 2nd Class
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Re: 3.0 to 4.3 Questions

Howard Sterndrive said:
the only way to do the 4.3 swap would be to buy a complete donor boat
Click to expand...

Sounds reasonable and after doing some reading the 4.3 can produce pretty good H.P., up to 300 H.P. with out breaking the bank. I like the idea of a slightly smaller engine, length and weight that can make an easy 250 + H.P.

They are dirt cheap on craigslist and i'd perfer rebuilding one and knowing it's fresh as opposed to buying one that someone claims is in good shape for too much.
 
SeanMcl

SeanMcl

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Re: 3.0 to 4.3 Questions

tschmidty said:
A 4.3 is not really a great engine for trying to get two adult skiers up anyway. Nor is a 17 foot trihull. For that matter why do you really want to get two skiers up at the same time?
Click to expand...

Skiing two up is fun. Keep the rope lengths the same though, so the back skier can't clothesline the front skier. They can still crash into each other, so be safe.

FWIW, we used to ski two 175 lb adults behind grandpa's 17 foot tri-hull with a 85 HP outboard. The prop was low pitched to pull up skiers, and top speed was about 25 - 28. If you want to ski now and do the motor swap this winter, prop way down and have fun.
 
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Cptkid570

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Oct 18, 2005
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Re: 3.0 to 4.3 Questions

What pitch prop are you running? $100 for a different pitched prop is a lot cheaper than buying a new engine.
 
SeanMcl

SeanMcl

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Re: 3.0 to 4.3 Questions

38special said:
Sounds reasonable and after doing some reading the 4.3 can produce pretty good H.P., up to 300 H.P. with out breaking the bank. I like the idea of a slightly smaller engine, length and weight that can make an easy 250 + H.P.
Click to expand...

Keep in mind that you only have 5000 RPM or less to play in. Also, you are looking for power in the 2000+ RPM range. If you have the boat propped for 50 mph at 4800 RPM, and want to ski at 25 mph, you can see at 25 mph you will be at pretty low RPM. Peaky motors need not apply.

http://www.hotrod.com/techarticles/engine/113_0208_chevy_43l_262ci_v6_engine_build/index.html

This article at Hodrod.com shows a healthy 4.3, 9.08 compression, and the torque curve is pretty flat. It's making 194 HP, 292 ft/lbs at 3500 RPM and 285 HP and 311 ft/lbs at 4800 RPM. If it makes over 200 ft/lbs at 2000 RPM, I'd say you have a winner.
 
S

sethjon

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Re: 3.0 to 4.3 Questions

4.3 will definitely pull 2 skiers. There are other things to consider...the prop, the weight of the skiers.
 
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38special

Petty Officer 2nd Class
Joined
Mar 9, 2010
Messages
129
Re: 3.0 to 4.3 Questions

SeanMcl said:
Keep in mind that you only have 5000 RPM or less to play in. Also, you are looking for power in the 2000+ RPM range. If you have the boat propped for 50 mph at 4800 RPM, and want to ski at 25 mph, you can see at 25 mph you will be at pretty low RPM. Peaky motors need not apply.

http://www.hotrod.com/techarticles/engine/113_0208_chevy_43l_262ci_v6_engine_build/index.html

This article at Hodrod.com shows a healthy 4.3, 9.08 compression, and the torque curve is pretty flat. It's making 194 HP, 292 ft/lbs at 3500 RPM and 285 HP and 311 ft/lbs at 4800 RPM. If it makes over 200 ft/lbs at 2000 RPM, I'd say you have a winner.
Click to expand...

I read that article, the most expensive part of that build is the cam and lifters along with the intake and still the price is not bad at all for that kind of H.P. from a 4.3. The heads are the limiting factor on the 4.3s unless you are willing to shell out for a nice set of aluminum heads.

Still to get over 300 H.P. from a 4.3 with little more than a pocket port job and nice cam and lifters is pretty cool.
 
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