New 5.7 vs. Old carb 5.7

Limestone

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Sep 23, 2001
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I have a 1988 5.7L 260hp Mercruiser with 800 engine hours which is generally well maintained and running well. Given the engine's age, would a new 5.7L (350 MAG MPI) have a lot more "real" horsepower? Although everybody talks about the new efi engines getting "better" fuel economy, what kind of real world fuel economy improvement could I expect (1%? 10%?, ...). Thanks
 

TilliamWe

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Re: New 5.7 vs. Old carb 5.7

the new 350 MAG MPI is rated at 300hp. And that's at the prop. Not sure where your 1988 260 was rated at. Others on here should know.<br /><br />I assume that 260 is a carb. The difference in fuel economy would come from the fact that the 350 MAG MPI is fuel injected. Not that it's newer. Interestingly, Merc only offers a 2 barrel carb on the 5.7 nowadays, before they go straight to the MAG MPI.
 

Limestone

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Sep 23, 2001
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Re: New 5.7 vs. Old carb 5.7

I see a lot of talk about EFI getting better fuel economy then carb engines. Can anybody quantify the difference? (The same goes for dual prop legs).
 

magster65

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Re: New 5.7 vs. Old carb 5.7

I recently saw (in a performance offshore application) a 5.7 MPI replaced with a 5.7 carb'd. Fuel economy was that MPI definately used more fuel but it outperforms the carb'd engine easily. I suspect if you were to throttle back to where the performance is equal, you'd see a slight advantage to the MPI motor. The 2 bbl merc carbs are how many cfm? I thought they were up around 650...
 

bluewater19

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Apr 25, 2003
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Re: New 5.7 vs. Old carb 5.7

I think the 2bbl mercarb is around 425cfm. If they were 600 or bigger why would people want to switch to a 4bbl?
 

magster65

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Re: New 5.7 vs. Old carb 5.7

They look bigger than 425?<br />I heard that they stopped making the 4bl and just have the 'giant' 2bl's now. Bad info?
 

rbezdon

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Jun 20, 2004
Messages
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Re: New 5.7 vs. Old carb 5.7

mag, you may be mixing the info on the 2bbl TBI airhorn and the 2 BBl carb. The 2BBL TBI is closer to 600 (doesnt need the fuel dispersion stuff in the airpassage). The 2 BBL carbs sre in the 400s typically. And this is not for Marine. Typically TBI was not available for marine. They went carb or full MPI.
 
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