4.3 MPI vs. Carb

kvkon

Seaman
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Aug 6, 2006
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64
So my 4.3 MPI Vortec has a cracked block and I need to build a new motor. What's the HP difference if I go back to basics with a carb engine? I know I'll need a distributor, carb and intake manifold and lots of wiring mods. Anything else that I have to change? If I use flat top pistons in carb or MPI build will it run on regular gas?
 

tonyjh63

Petty Officer 1st Class
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Apr 23, 2013
Messages
242
Just out of curiosity, why would you rather build a carb-ed engine instead of an MPI? My 4.3 is carb-ed, and I wish it were MPI...
If you do go carb-ed, at least go 4bbl instead of 2bbl.
 

alldodge

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2bbl 190HP, 4bbl 205HP, MPI 220HP

Unless your going to build some real power, just get a stock vortec motor and put your stuff back on it
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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the carb'd vortec 4.3 was near the edge of reversion and detonation, the MPI vortec 4.3 is on the ragged edge because the ECM can back off the timing as needed.

I would simply put a new or re-man long-block back under your MPI stuff.
 
Last edited:

kvkon

Seaman
Joined
Aug 6, 2006
Messages
64
2bbl 190HP, 4bbl 205HP, MPI 220HP

Unless your going to build some real power, just get a stock vortec motor and put your stuff back on it

OK that makes sense. I figured I'd find a core and build my own long block since I've done a few engines before. Would I be able to run flat top pistons on regular gas?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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factory GM Boat/Truck/Generator/Trash-pump engines are flat top with 4-reliefs

just build it stock so you dont have to re-program. if you change the combustion mix (CR, cam profile, etc) , you need to re-program the ECM.
 
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