swap 3.0 with 4.3

[rdobe99]

i have a 1992 maxum 18 ft with cracked block i wanna now is it a complete nightmare to put a 4.3 in its place,i know i need different exhaust tube,and gearing and prop,and probly have to add motor mounts but will it fit,will the wiring match as far as the plug,can anybody fill me in with any info,thanks for your time,you people always help,

 

[jerryjerry05]

Re: swap 3.0 with 4.3

If the replacement is close to the same year,most things will hook up.
Just remember nothing will ever just slide right in .J

 

[rdobe99]

Re: swap 3.0 with 4.3

i guess i left out the bad engine is a 3.0 ,i want a put a 4.3 v 6 in its place if at all possible i am mechanical with 2yrs of marine expierence but it was a few yrs back,i just dont want to start a nightmare when i could just put another 3.0, 4 cylinder real easy,but would prefer a 4.3 v6.if at all possible lookin to hear if anybody has been through this process ,THANKS dAVE

 

[solar7647]

Re: swap 3.0 with 4.3

Well I would just get a new long block and rebuild the 3.0 and re-drop it in. It will be less time, cheaper and easyer. You will have to change alot switching.
MO is it would be more money time, and head ache then it would be worth when done. I also would question if the drive ratio would be the same, so you could end up haveing to get a hole new drive.

 

[rdobe99]

Re: swap 3.0 with 4.3

well poop.lol,i thought it would be fun for some more power,does anybody know where i can a 3.0 long block for a reasonable price of even a whole motor ,i had a line on a nice 4.3 there goes my dreams of granger,hehe thanks again Dave

 

[rdobe99]

Re: swap 3.0 with 4.3

hey solar this is probly wothless too, i can get a perfect 3.7 from a freind if i want it,how about that sawp out,probly a nightmare too,or i can get 3.7 and trade someone for a 3.0 with some cash involved,any body,meaning i will be the one payin, thanks again

 

[solar7647]

Re: swap 3.0 with 4.3

well a 3.7 would be easyer to swap then a 4.3, as far as front mounts will be similer and the transom mounting would also be similer if not same, but the drive may be the issue 3.7L is 1.84:1 ratio same as 4.3L. I beleive the 3.0 is 1.94 so that could be an issue.

It could be better choice if engine is in good condition and was well kept. Plus you would get close to the same HP as the 4.3 since the lower end 4.3l starts at 190hp and you can get 190hp from the 3.7.

 

[rdobe99]

Re: swap 3.0 with 4.3

well solar you seem really smart with this stuff,tell me if this is true then i heard horsepower was measured differently when they made 3.7 engines and the horsepower of 3.7 is not more than the 3.0 and it will basically be the same on the water true or not,in your opinion thanks again Dave

 

[solar7647]

Re: swap 3.0 with 4.3

No that is not tru....a 3.7L comes in multple HP, 165hp, 170HP, 180HP and 190HP. The larger HP versioins differ from the smaller ones with "bolt on" parts. Four barrrel carb instead of two barrel, oil cooler, ect. If you look in my signiture you will see a link to a thread I am doing on 3.7L rebuild.

There are also differance between years such as heat exchangers, cams, oil pump.

 

[ken_23434]

Re: swap 3.0 with 4.3

If you do the swap, you should try to get the complete engine (take engine out of junk boat) so you have the manifolds, carb, distributor etc...

The wiring on all the Mercruisers I have seen all have a "cannon plug" near the rear of the engine. The "engine harness" ends at that plug, and the "boat harness" plugs into the other side. That plug is essentially the same for all the Carb'd Mercruisers.

So, if you had a complete Mercruiser 4.3 with carb, the wiring should be just a matter of plugging in that one round connector.

If you went with a newer 4.3 with fuel injection, then I have no idea what that would involve (might be the same if the ECU is on the engine side of the cannon plug).

The 4.3 has engine mounts on the side where the 3.0 has a front engine mount. You would have to make sure you could mount the side mounts onto something structural (stringers). That would probably involve epoxying in some additional wood in the engine compartment to create a strong mounting point.

 

[solar7647]

Re: swap 3.0 with 4.3

The wiring on all the Mercruisers I have seen all have a "cannon plug" near the rear of the engine. The "engine harness" ends at that plug, and the "boat harness" plugs into the other side. That plug is essentially the same for all the Carb'd Mercruisers.

So, if you had a complete Mercruiser 4.3 with carb, the wiring should be just a matter of plugging in that one round connector.

It is correct that all Mercruisers use such a plug but the number of pins in the plug can very from 8-14 pins and would require adapters to allow them to plug into differant harness, for example if he were to simply upgrade to a new post 2006 3.OL he would need to get an adapter that would change the harnes from 14 to 10 pins so that it would plug into his wiring.

 

[cooter2506]

Re: swap 3.0 with 4.3

Rdobe99 I believe you are correcton the hp differences. When the 3.7 was out it was measured at the flywheel not the prop like they are today. So basically you can take away about 25-30hp to get a at the prop hp measurement. I would just try to find a donor boat with a good 3.0 to remove and drop in yours

 

[solar7647]

Re: swap 3.0 with 4.3

Rdobe99 I believe you are correcton the hp differences. When the 3.7 was out it was measured at the flywheel not the prop like they are today. So basically you can take away about 25-30hp to get a at the prop hp measurement. I would just try to find a donor boat with a good 3.0 to remove and drop in yours

This only applies to outboard motors. Outboards HP is measured at the prop because the engine and drive unit are connected and dont change they always have the same combo of power heade to drive unit.

Inboard and sterndrive engines are measured at the flywheel because the drive unit can change based on several factors and this will change the @prop Hp so they dont rate them with @prop HP because the engine manufacture dosnt know what ratio of the drive you are bolting it to, it could be a bravo, alpha Gen 1 or gen 2, it could be 1.81,1.91 or 1.94 ratio it could be a jet drive, or a surface drive. Point being every type of drive will have a differant Hp lose.

If you look at the specs of motors on Mercs website you will see that inboard and sterndrive engines have a HP rating but outboard have a @prop HP rating.

So with that said the best way to get the @prop HP of a sterndrive or inboard with out doing a hole lot of math is to figure a 10% reduction.

With all that aside the most important aspect of a marine engine is Torque not HP. Torque is what moves a boat witch is why diesel engine are the best marine motors.
HP is just a measurment of torque over a period of time and really isnt an acurate measurnment of power, its better to use watts.

 

[rdobe99]

Re: swap 3.0 with 4.3

o boy,well im lost now i want more engine but i guess im not gonna get it,thanks to all of you, Dave

 

[solar7647]

Re: swap 3.0 with 4.3

o boy,well im lost now i want more engine but i guess im not gonna get it,thanks to all of you, Dave

Sorry to confuse you! You can get more engine, its just there are many ways depending on your buget, time, and mechanical know how.

If I were you I would just stick with a new 3.0L long Block. you can get them for a good price and it will be pretty easy to build. I think you would be surprised in the differance between a new 3.0 and the old 3.0. It will have a little more pep, and since you will be rebiulding it you could find ways to add some power.

Good luck