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Replacing 357 Carb with 383 MPI

N

NF22

New member
I am replacing my 357 mag carb to a 383 mag mpi in my 88 Senator.

I was going about 72-73mph with the 357, anyone know what I could expect with the 383? I would think maybe 1 or 2 mph. Will there be a significant difference in fuel economy?

Nothing but problems with the 357 I got put in a couple years ago. Merc gave me a replacement under warranty end of this summer and still more problems, so now I'm upgrading to the 383.

I went from a stock 350 and 58-60 mph to the 357 and hit 72-73. So I am curious about my jump of another 25hp to the 383.

Any and all information would be very grateful.

Thanx
 
What was done to the 357 to gain 10-plus mph over the 350. A 350 to a 357 is only 7 cubic inches.

What makes me scratch my head is that you went from a 350 to a 357. That is only 7 cubic inches bigger and gained 10 plus mph. Now you estimating only a 2 mph gain out of a 383 and thats 26 cubic inches bigger.

Are we talking cubic inches or horse power because the merc 383 mag has 350hp
 
There were no mods done to the engine. I had the entire floor and stringers replaced the winter I put the 357 in so maybe it took out a ton of weight.

I went up 65 hp from the 350 to 357. So I will be gaining an additional 25 hp going to the 383.

Sorry for the confusion. I know less then nothing about engines. Just went through 2 miserable years with the 357 Carb. Tons of popping out of that engine and cant wait for the MPI and less headachs.
 
Here is what I got so far on my enchanter. 1.47 ratio alpha (SE).
350/260hp=64mph w/23p stainless
355/325hp=69mph w/23p stainless
383/est500hp=76mph w/26p stainless turbo before lower unit blows out. Motor pulls hard and I feel with a nose coned lower, I will reach 80mph. Still very early on the setup and with some play time with the setup, it will be faster than I want to go! Not sure how these hulls compare but I believe they are close. Mine is a 21'er with a pad but the enchanters have a hook in the rear.
The carb motor is a good way without going to expense of the EFI. I got all my parts through MK Hammer and he has me setup with the good parts and told me flat out what will and will not work. Also he said where I need to go more and what is more than I need. He did a great job on helping me not go overboard on parts cost. He also offers turn key setups that will be less cost/ more power than a merc replacement motor!
 
Thanks YF

I can't wait to get rid of the 357. Those engines are haunted. Had the carb replaced 3 times, new ignition and starter put in. Tons of water testing and time out of the water. Plus ton of $$$$$ spent on all of it. 2 engines in two years. If I knew of all the problems a carb engine can give rather then the mpi, I would have spent the extra $$$ in the beginning to avoid all of it.

I have to give Merc credit though, they stepped up at the end and have allowed me to trade in my 357 and they are giving me my money back and all I have to do is pay the difference between the cost of the 357 and 383. They are paying for all the mechanical work here on out. Very happy that they stepped up at the end.
 
Something doesn't sound right with that whole deal. Millions of people have been running carbs on small block Chevys in boats for 50 years or more so I can't see blaming the fact that its carbed for the problem. A 357 (if that means 357 cubic inches) is just a .040" overbored 350 and there are tons of those out there as well. If the mechanic couldn't get a carbed small block to run right then if it were me, I'd find a new mechanic. If the boat was giving you "driveability" issues then why replace the starter? I'm not one of those guys who is against new technology (I own a 400hp turbo 4 cyl car) but its been my experience that when an MPI'ed boat doesn't run right, it is far more difficult to get to the root of the problem than with a carbed set up. I hope that the new engine works perfect for you, it just seems strange that a mechanic couldn't figure out why a carbed Chevy wouldn't run right.

Good Luck!

John
 
I agree I would find a new mechanic if he could not figure out why it was popping and spitting when it was a carbed engine. I am a carb person thats what I like. But I will agree fuel injection is the best way. But I would rather take the thousands of dollars it takes to get injection right on a modified engine and use it somewhere else.

Fuel injection is killer on a stock engine or a mild built engine. But will empty your wallet quick when big upgrades are done to a engine.
 
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