4.3 Carb v 4.3MPI

[Superjetjim]

Is the MPI really 25hp more powerful that the carb or is it just marketing?

Any other real advantages of one over the other? Starting / economy etc?

Has anyone owned both and care to share their opinion please?

 

[Scott Danforth]

just a year before the 4.3 MPI, when there was a 4-barrel carb, the power was rated at 220hp

as far as economy, no. as far as ability to make power, no. easier to start - somewhat. the only reason it shows slightly more power is you can take it slightly closer to the edge of the envelope with knock than you can with a carb.

EFI in a boat doesnt shine until there is variable valve timing.

only you can determine if Multi-Port fuel injection is worth it to you. To me, its an extra $2000 worth of stuff to go wrong on top a $2500 motor

 

[Lou C]

I think the main advantage of throttle body FI or port EFI is better cold starts and smoother running when cold. However as far as ease of repair & parts cost carbs are easier to deal with. You’re not having to track down intermittent electrical problems and deal with NLA fuel injection parts when the boat gets to be more than 10 years old. All the carb parts you would ever need you can get from Edelbrock & Holley and even Quadrajet parts are widely available in the aftermarket. Low pressure electric pumps are much cheaper that OEM EFI pumps. Even better is the old school mechanical pumps you can use on the Pre Vortec engines. Inexpensive, reliable & not affected by electrical faults.

 

[jimmbo]

Much easier to hop up a Carbed engine than an Injected engine.

 

[achris]

Has anyone owned both and care to share their opinion please?

I have. Had a 1994 4.3LX, currently have a 4.3MPI. Both in the same boat so the comparison is valid...

I loved the LX, and only have one regret about the MPI. I wish I'd put the MPI in years before I did! Apart from the usually maintenance (oil and filters) the ONLY thing in 16 years I've had the replace is the IAC valve. That was $45. No more fiddling with carbs for me.. the MPI is ultra reliable and just does everything that little bit better than the carbbed engine did...

Some people will tell you that 'you can't fix an MPI if it breaks down at sea'... While that might be true, the fact is that MPI engines RARELY break down, and most of the time when they do, they will still get home (unlike points and carbs. When they stop working, you're dead in the water).

So, I'm not a young bloke who's never owned or worked on points/carbbed engines, I'm 62 years old and cut my teeth on early engines. But I much much prefer injected over ancient...

Chris...

 

[jimmbo]

I do enjoy watching people who have only driven FI Cars/Trucks trying to start a Boat with a Carb. It was too bad they couldn't engage the Starter in Gear, some of them may have made it across the Lake on Battery

 

[QBhoy]

Hi. Here are some facts. The 4.3 mpi and is indeed more powerful than the carb. It is also more fuel efficient too. It has the ability to run smartcraft too.
Downside…I wouldn’t want to have to replace one for new. Much dearer than a carb. But if there is a choice of two boats and only a grand or two different price used. Mpi all the way.
The only rpms the 4.3 uses more fuel than the carb…is at full throttle. Only by a few litres an hour. But at full throttle, you are getting 30hp more than the 4.3 tks
The guys that don’t like them…mostly hav never had one to see how good they are. I’d say.
Only carb 4.3 that might compare was a reman version that quicksilver offered a wee while ago. That claimed 220hp. Not sure how it managed that though. Perhaps rated at the flywheel and not the prop as per normal.

 

[Scott Danforth]

Only carb 4.3 that might compare was a reman version that quicksilver offered a wee while ago. That claimed 220hp. Not sure how it managed that though. Perhaps rated at the flywheel and not the prop as per normal.

nope, prop rated.

 

[QBhoy]

nope, prop rated.

Were they ever fitted in a boat from factory? Always thought they were after offered quicksilver things. Hp rating always seemed more that original versions. No idea why.

 

[Lou C]

Just a caution:
Both Merc & Volvo make parts for these throttle body & MPI systems go NLA after the boat is about 10 years old. With carbs this is not an issue. Just something to keep in mind if you buy older boats. I can get all the parts I need for a Quadrajet, that hasn’t been built since 1990. New Holleys & Edelbrocks are available and parts for them are everywhere. That is far more important to me than any advantages the MPI has….

 

[Rick Stephens]

He he, with a pre-balance shaft roller cam 4.3 block, Vortec heads, performa intake and 1409 carb, I don't give up much power to the MPI. Balance shaft takes 15 horses to spin off the top. This damn 4.3 runs!

I'd still take an MPI in an instant over it.

I have two chevy pickups, my 2000 work 3500 with a 7.4L and a 2007 3500 with an 8.1L. They ALWAYS start and run perfectly. Don't get crap for milage, which sucks these days, but the 7.4 weighs in at 12,000 pounds with all the welding gear on it and it scoots.

MPI all the way.

 

[Superjetjim]

Just a caution:
Both Merc & Volvo make parts for these throttle body & MPI systems go NLA after the boat is about 10 years old. With carbs this is not an issue. Just something to keep in mind if you buy older boats. I can get all the parts I need for a Quadrajet, that hasn’t been built since 1990. New Holleys & Edelbrocks are available and parts for them are everywhere. That is far more important to me than any advantages the MPI has….

Hi Lou,

Thanks for your post, are you suggesting the parts for MPI are no longer available after 10 years (or there is a chance they might no longer be available)

 

[achris]

Hi Lou,

Thanks for your post, are you suggesting the parts for MPI are no longer available after 10 years (or there is a chance they might no longer be available)

The earlier MPIs can have parts difficultly, but everything for my engine is still available (16 years on).

Chris....

 

[Lou C]

Same thing with Volvo Penta.

 

[Searay205]

My take is the MPI engines are very repeatable and friendly when they work correctly, which most of the time the do. My opinion is I would take a 5.0 TKS over a 4.3 MPI. I would also take a 5.7L carb over a 5.0 mph. Problem is they never offer those options its either 4.3 tks or 4.3 mpi

 

[achris]

My take is the MPI engines are very repeatable and friendly when they work correctly, which most of the time the do. My opinion is I would take a 5.0 TKS over a 4.3 MPI. I would also take a 5.7L carb over a 5.0 mph. Problem is they never offer those options its either 4.3 tks or 4.3 mpi

You're comparing apples and oranges... Stick to one base engine and make your case.

Chris...

 

[Scott06]

You're comparing apples and oranges... Stick to one base engine and make your case.

Chris...

He is saying for the same hp rating he would take the larger displacement, lower performance carbed engine. both groups are 220 hp and 260 respectively….

 

[Searay205]

Scot06 interpreted my mess correctly. I would always prefer the higher horsepower and happy with a carb engine over MPI BUT they don't offer a carb 350 just 5.0 tks or 5.0 mpi, sooooo I would take the 5.0 mpi. Actually the Searay 205 was offered with 3 engines the 4.3 MPI, the 5.0 TKS, the 5.0 MPI. Very rare to see the 5.0 mpi in a 205. The 4.3 MPI option was $3K more than the 5.0 TKS. So no brainer take the 5.0 TKS. The 5.0 mph was only $80 more than the 4.3MPI. My take is the 5.0 mpi wasn't pushed. on the customers because it just to much motor for the boat and borderline dangerous. like 63mph on stock prop and black ice felling. I switched to a high 5 prop to take some speed off it, now its the best powered boat I ever been on, tons of torque and 55 with 1 or 8 people aboard!!!

Advantages to carburetor:
1) quiet, no fuel pump noise
2) low cost, easy to trouble shoot and fix
Disadvantage of Carburator
1) Will not run as good as an MPI engine, will not start as easy, will not idle as well, will act like a mid 70's car
2) most vapor lock, have to know how to clear a flooded situation have to be somewhat mechanically inclined
Advantage of MPI
1) drives like modern car. turn key and it starts, idles perfects, never floods out, excellent throttle response (no lag), no hesitation, anybody that can start a car can start an MPI engine.
2) Expensive to fix if your not mechanically inclined but they don't fail that often. Especially the non-cat engines. Cat engines fail post o2 sensors but there is a work around...

 

[Lou C]

Vapor lock is one problem I never had with the 4bbl Quadrajet but I’m also at sea level I have heard it’s more of a problem at high altitudes where the barometric pressure is lower…

 

[jimmbo]

Vapour Lock occurs in the Fuel Line, upstream of a Fuel Pump. Things like Percolation, which can sometimes give Symptoms that are similar, but are caused by heated fuel overloading a Carb when the Inlet Valve opens after a Hot Soak.