Merc 4.3 MPI vs carb

[bruceb58]

The 5.0 (even the tks 5.0) is there too.

Yes..and the TKS showed lower fuel consumption.

No..the 5.0MPI is not equivalent to the carb'd 5.7. They have a completely different WOT RPM rating hence the peak HP looking the same.

 

[QBhoy]

Doesn't show fuel consumption...but I'd like to see a carb 5.0 or 5.7 show these revs and speed as a comparison !

 

[QBhoy]

They are surely comparable as in the boats that used to have a 5.7 carb now have a 5.0 mpi. Just like the new 4.5 mpi replaces the 5.0 mpi.
The 5.0 tks only shows lower in one, maybe 2 of the Rev ranges from memory....and has at least 40hp less than the mpi.

 

[bruceb58]

Doesn't show fuel consumption...but I'd like to see a carb 5.0 or 5.7 show these revs and speed as a comparison !

My carb'd 7.4L does better than that...doesn't mean much.

Need identical boat with identical displacement to compare MPI vs carb.

 

[bruceb58]

That website shows nothing on how they came up with their numbers. Did you see what types of boats they were using for their tests? How can you assume that a 5.7 carb'd engine was tested on the same boat as a 5.0MPI boat?

 

[QBhoy]

That website shows nothing on how they came up with their numbers. Did you see what types of boats they were using for their tests? How can you assume that a 5.7 carb'd engine was tested on the same boat as a 5.0MPI boat?

You didn't just ask that question....oh oh. The defence rests.

 

[bruceb58]

Waiting.......

 

[tpenfield]

Googling of an apples-to-apples comparison does not come up with much. The only thing that I found was a torque/hp curve that showed MPI only slightly greater than a carb'ed engine.

I think the key benefit is starting, which for marine engines is not always a given

 

[QBhoy]

The horse power (if we are comparing carb and mpi of same displacement) is vastly different. Massively more powerful.

 

[tpenfield]

The horse power (if we are comparing carb and mpi of same displacement) is vastly different. Massively more powerful.

Maybe. . . but I have not seen, nor could find, any data that supports that statement.

 

[QBhoy]

Maybe. . . but I have not seen, nor could find, any data that supports that statement.

What do you mean TP ?
The 4.3 carb is 170/190hp generally, the mpi is 220
The 5.0 carb is 220/230, the mpi is 260
The 5.7 carb is 250/260, the mpi is 300...
It goes on....I thought this would be well documented and clear to see...I thought most knew the specs for these engines ?

 

[jimmbo]

I have compared my boat, on the water, which has the 5.7 carbed(2bbl) VP(260hp) with the exact same model of boat with a FI 5.0 VP(260hp). I had much better holeshot and a higher top speed. When I replaced the 2bbl 500 cfm Holley with a 650 Holley Spreadbore and gained an 11% increase in RPM it was making more than 260HP

 

[bruceb58]

What do you mean TP ?
The 4.3 carb is 170/190hp generally, the mpi is 220
The 5.0 carb is 220/230, the mpi is 260
The 5.7 carb is 250/260, the mpi is 300...
It goes on....I thought this would be well documented and clear to see...I thought most knew the specs for these engines ?

The MPIs are all rated at higher RPM.

You still haven't come up with these Mercruiser fuel economy numbers comparing the same displacement engines with MPI vs Carb and the exact same boat. Thought you had them at your fingertips!

 

[jimmbo]

The MPIs are all rated at higher RPM.

You still haven't come up with these Mercruiser fuel economy numbers comparing the same displacement engines with MPI vs Carb and the exact same boat. Thought you had them at your fingertips!

400 rpm higher. Which is a little less than the increase I got when I swapped the 2bbl for the 4bbl

 

[QBhoy]

The MPIs are all rated at higher RPM.

You still haven't come up with these Mercruiser fuel economy numbers comparing the same displacement engines with MPI vs Carb and the exact same boat. Thought you had them at your fingertips!

So what if they are rated at higher rpm ? The fact remains they are more powerful. Someone said they have never seen evidence of this...what has happened to you guys ?
5.0 mpi is only rated 200 rpm higher than carb, just to correct a point.

 

[QBhoy]

400 rpm higher. Which is a little less than the increase I got when I swapped the 2bbl for the 4bbl

Not always. The 4.5mpi is though.

 

[QBhoy]

The MPIs are all rated at higher RPM.

You still haven't come up with these Mercruiser fuel economy numbers comparing the same displacement engines with MPI vs Carb and the exact same boat. Thought you had them at your fingertips!

Bruce have you been taking crazy pills ?
I sent them over.
With regard to the different boat thing...I never mentioned anything about the different boat. Not that that matters. An engine doing a certain rpm is an engine doing a certain rpm.
No need for smart arse comments if you are being a bit stupid about it in the first place. Didn't want to make a fool of you.

 

[QBhoy]

I have compared my boat, on the water, which has the 5.7 carbed(2bbl) VP(260hp) with the exact same model of boat with a FI 5.0 VP(260hp). I had much better holeshot and a higher top speed. When I replaced the 2bbl 500 cfm Holley with a 650 Holley Spreadbore and gained an 11% increase in RPM it was making more than 260HP

Jimbo...the acceleration, yeah I can totally see that. The top speed will surely be related to the dialled in prop you are running (enertia) and probably driver experience. Lots of variables there to think about. All things being equal...physics would suggest they would be exactly matched for top speed.

 

[QBhoy]

Yes..and the TKS showed lower fuel consumption.

No..the 5.0MPI is not equivalent to the carb'd 5.7. They have a completely different WOT RPM rating hence the peak HP looking the same.

This still cracks me up....
They are not comparable...the hp only looks the same...IT IS THE SAME !
What does the extra 200 rpm have to do with it ? It's just engine evolution.

Are you saying that if you got a smaller pitch prop on a 5.0 carb (standard engine) and allowed it to Rev an extra 200 rpm.....it would make an extra 40hp ?

Can you see how you are being silly ?

 

[tpenfield]

QBhoy

I think what is being compared is how the engines are set up by the manufacturers. Carb vs MPi. That is not to say that the carb engines could not achieve similar horsepower, it is just a matter of what they are configured to do. there is no question that many MPI engines are configured to get more HP than their carb'd equivalents.

On the flip side of the coin . . .

My Carb'd 7.4L was rated at 330 HP (1991 model)
My MPI 7.4L engines are rated at 310 HP (1996 model)

So, why are the MPI engines in my current boat 20 HP less than the same size engine in my prior boat? :noidea:

What I don't see information on, as I search the web, is if you can or cannot achieve significantly more HP/Torque from an MPI engine vs. a carb'd engine. I would think that you could, but I'm not sure if there is specific testing/data to support that. I think the same goes for fuel efficiency. I would think that the MPI engines are more efficient, but by how much and is there testing to support it.