Is it worth swaping a 4.3 MPI for a 5L ?

meinmelb · **Posted:** Fri Feb 13, 2015 3:14 am

Hi Guys

Just in case you have missed my previous thread, I partially sank my boat in Salt water and the motor was almost submerged. I have replaced the starter motor as it died, but everything else is currently running fine. "Currently"?

I am being paid out for the motor and have an option on a complete ready to drop in Mercruiser 5L carb motor for $3k (2006 with 100hrs and thunderbolt ignition). With labour etc this is about the same cost as all the repairs on my current motor which is a 4.3MPI.

Question: Considering both the 5L carbie and the 4.3L MPI both produce 220HP is there any advantage in upgrading to the 5L. It is about 80ks heavier, will use about 2L per hour more fuel, but will there be any noticeable performance improvement? It might be reasonable it expect that the greater engine capacity would produce more torque lower down the rev range, but as a carb compared to a modern multipoint fuel injection is it really that much more then the 4.3MPI?

If I do go for the 5L is there any upgrade options that I can do to increase the HP? Say to the 260hp mark with out major modifications?

deafwish · **Posted:** Fri Feb 13, 2015 4:03 pm

Hi Mark,

I can supply & take an oil sample from your 4.3 to determine whether any excessive bearing/ cam wear is already happening.
While this won't show future electrical problems, it may give you another year's worth of boating prior to a potential engine swap.
Oh & the V8 will be light years better a performer, when compared to the V6 on a boat your size.
What carb is it coming with? Is it a Vortec engine (8 bolt intake manifold)?

GottWhat · **Posted:** Fri Feb 13, 2015 6:14 pm

According to the FW Fast Facts, the 4.3L 220HP and the 5.0L have the same fuel burn at 3500 RPM but the 5.0L burns 1 more GPH at 3000 RPM. However, the V8 is moving at 32 MPH whereas the V6 is doing 29 MPH.

I would think the V8 torque would help with acceleration but I have no proof.

FastFacts: http://www.fourwinns.com/upload/Documen ... s_2004.pdf

meinmelb · **Posted:** Fri Feb 13, 2015 9:15 pm

deafwish wrote:

Hi Mark,

I can supply & take an oil sample from your 4.3 to determine whether any excessive bearing/ cam wear is already happening.
While this won't show future electrical problems, it may give you another year's worth of boating prior to a potential engine swap.
Oh & the V8 will be light years better a performer, when compared to the V6 on a boat your size.
What carb is it coming with? Is it a Vortec engine (8 bolt intake manifold)?

Thanks Mate!! I will take you up on this offer as I have not thought of it. Great option to find out what is going on inside the motor, whereas I am planning to replace all the electrics, sensors, wiring loom etc. Knowing the internals are not about to blow up spoon is cleaver thinking!! Please can you let me know how I do this and what the costs are, I would appreciate that thanks!

The V8 option is a 2006 5L carbie version which I believe is the vortec heads. It has done about 80 hours and the owner re-powered his 22ft cuddy cabin with a 6.2L MPI and now wants to sell this motor. It has the Std carb from Factory.

I have been researching the differences between the 4.3MPI and the 5L carb, and general consensus is that the 5L "should" have more torque, an "Should" develop this torque lower in the rev range. Nothing concrete.

I have left a message with a contact of mine at Mercury Australia. He knows the development engineer that specs the various Power packages for boat builders and is also the go to guy for re-power solutions so hopefully he can offer some advice. If the 5L does have additional usable power then I can swap it out at virtually no cost to me so essentially a free swap out, but still not convinced it is worth it.

ric · **Posted:** Fri Feb 13, 2015 9:27 pm

I have a 220hp 5.0 merc in my boat. That thing is a beast dude, so much torque. It puts my 3600lb 22ft cuddy cabin with 8 adults on plane only using 3/4 throttle and top speed at 48 on the GPS (around 8000lb fully loaded like that). I average 5gph @ 3000rpm at 28mph with 4 people and will get on plane almost off idle.

Do that with a 4.3. I don't think so. DO IT!!!!!

Protip: Swap the 2bbl/intake manifold for a 600cfm marine 4bbl setup and it makes 280hp.

Wylie_Tunes · **Joined:** Mon Oct 01, 2012 10:21 am **Posts:** 176

Why not go with a 5.7? Same block externally as the 5.0L.

deafwish · **Posted:** Sat Feb 14, 2015 1:17 am

Clarify what carb it has, as it could be a crappy Mercarb, Holley 2300 or even a 600cfm 4BBL.
A 2300 Holley would give you craploads of torque with reasonable economy...
Swap you my 5.7 GL (334H) for the 5.0L Vortec?! ;-)

ric · **Posted:** Sat Feb 14, 2015 6:31 am

A mercruiser 5.0 220hp engine has a tiny mercarb. Quite honestly it has NEVER given me an issue. The boat starts within half a second of turning the key no matter what the outside temp is. The engine itself is a vortec 5.0 which can easily make 300hp with just intake upgrades (carb, intake manifold, and cam).

I would never pick a 4.3 over a 5.0 if given a choice.

meinmelb · **Posted:** Sat Feb 14, 2015 7:25 am

Wylie_Tunes wrote:

Why not go with a 5.7? Same block externally as the 5.0L.

Cause you cant by a 5.7 complete Mercruiser motor for cheap enough to make the project viable in Australia. most are AU$7K and up for a half decent one.

deafwish · **Posted:** Sat Feb 14, 2015 5:08 pm

ric wrote:

The engine itself is a vortec 5.0 which can easily make 300hp with just intake upgrades (carb, intake manifold, and cam).

At what RPM?!

Surface Interval · **Posted:** Sat Feb 14, 2015 6:31 pm

I would be curious which version and vintage the 5.0 is. There were several changes in the engine configuration over the last 20 years that affected GM stock engine power output, as much as maybe 100 hp in some cases. With any configuration you could probably gain power by changing some intake parts, but it may not be the same as a later model engine. More power is always nice, and a person can always throttle back some to save fuel. Significant power changes will require changes in your prop, and possibly may work best with a gear ratio change in the out drive.

meinmelb · **Posted:** Sun Feb 15, 2015 4:15 am

I have confirmed it is a 2006 5L mercruiser. Reading up on the interwebs it seems this model does have the vortex heads.

Then reading the hot rodders forums it looks like a new intake manifold and a 600cfm 4 barrel holley will add about 40hp. As a road vehicle a set of cams will add another 40+ hp but I am not sure if this is advisable in a marine motor as water can be sucked into the pistons.. ( not sure but rather be safe)

That will give me 260hp for reasonable money so might be worth it. If I can find a cam that is safe for marine use and increases torque low down I will take a look at that as well.

The Alpha drive I have is a 1:62 and is the same ratio as installed with the 5L from factory. I will retain the 19P High 5 prop as I want tree stump pulling low down power not high speed. But if I need to I will get a 21P

$3k for motor
$1K for manifolds and carb
$2k for installation
Less sale of existing motor for $2k
$4k for a 260hp V8 instead of the 4.3MPI v6....
Less $4K payout from Insurance company and technically is a free upgrade.....mmm makes for interesting conversations with the wife.....

ric · **Posted:** Sun Feb 15, 2015 8:27 am

Use the gm performance camshaft from the Ramjet 350 crate motor. It's the same cam used in the Mercruiser 350 mpi

TX H210SS · **Joined:** Thu May 27, 2010 9:10 am **Posts:** 1488

If the 5.0 checks out I say its a no brainer. I would prefer the Carb over injection personally. That fuel cell for the injection system is money waiting to be stolen from us all. The Carb is a bonus in my book. I wouldn't mess with modifying that 5.0 either. It will have more than enough power for your boat.

Oh, if it doesn't have remote oil filter setup....put it on now..best spent money right there......does the 5.0 come with wiring harness? Sounds like your making out well and good time to swap for huge bilge pump too.

deafwish · **Posted:** Sun Feb 15, 2015 3:03 pm

Your 5.0L may not pull the RPM to warrant going to a 4BBL & may just use more fuel than pump more air!

http://forums.iboats.com/forum/engine-r ... -gl-vortec

www.iFourWinns.com

Is it worth swaping a 4.3 MPI for a 5L ?

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