rod_stewart
Outstanding Contributor
In spring 2007 I swapped a 4.3 V-6 out for a small block 6.2 MAG MPI in my 1996 20 ft Blue Water Mirage, just because. I bought a complete remanufactured 6.2 drop-in package from Merc, so everything bellhousing forward was brand new.
The 6.2 is rated at 350 crank/320 prop hp, whereas the 4.3 was rated at 180 hp; so a big, big performance difference. The 6.2 runs great and I now have over 90 hrs on it. Very happy with it so far. The cruise fuel consumption runs at about 4-4.5 GPH which is not much different than the 4.3 was.
The 6.2 is intended for use with Bravo drives only, but I decided to retain my Alpha Gen II drive. I changed the original 1.81 upper drive for a used 1.47 that I bought on ebay, and bolted it up to the original lower gear case, with a new water pump, naturally. Works just fine. I then sold my 1.81 upper unit on ebay.
The 6.2 came with a Bravo bellhousing, which bolts right up to the existing Alpha transom plate. Fortunately the Alpha and Bravo inner transom plates are the same part number. The Alpha driveshaft splines are the same as the Bravo and fit right into the Bravo coupler on the engine.
The original exhaust Y pipe would have fit the new exhaust elbows just fine, except I went with Hardin 40 degree side hull exhaust tips instead. I wanted to use Silent Choice exhaust selectors, but the fiberglass cowling behind the engine is too close, and they just would not fit. So I just blanked off the Y pipe.
The front motor mounts had to be moved ahead about 4-3/8" on the stringers. Drilled new holes and filled the old ones. No problem.
The 6.2 is about 4-1/2" longer overall than the 4.3. My engine bay had plenty of room in front of the 4.3, as the Mirage was originally offered with a 350 MPI engine option. Both the 4.3 and the 6.2 engines are the same width to the outside of the manifolds.
The 6.2 is about 1 inch higher to the top of the flame arrestor cover nut, and I had to raise the engine compartment cover somewhat to clear it. No big deal.
The 6.2 came with a standard Merc 10 pin electrical connector, which fit right up to the boat connector. All gauges work fine, including the alarm buzzer. The buzzer signals low oil pressure, high temp, low lube oil level, and low cooling water pressure, as well as “soft codes” detected by the ECM. I had to reset the selector on the back of my tach from 6 to 8 cylinder, no big deal.
As far as weight goes, I figure I did not add more than about 70 lbs net. I can't notice that the boat sits any lower in the water than before. All in all a great swap.
Any small block GM V-8 will work as a replacement for the 4.3. The 5.0, 5.7, and 6.2 are in fact all the same Gen I GM small block that originally started life as a 265 cu in V-8 in the 1955 Chevy. They have different bores and strokes, heads, cams, cranks, etc. The 4.3 is actually the same block as the 5.7; with two center cylinders missing. Both 4.3 and 5.7 have the same bore and stroke.
The 6.2 (383 cu in) is actually made by using a 5.7 block with the standard 4”; stroke, and a 3.75” stroke crank, as used in the 400 cu in small block Chevy car engine, way back when. Since this crank has a longer stroke than the 350’s 3.48”; the morphed engine is referred to by the slang term “stroker”. Since the block is re-used from a previous car or truck 350; it will have been bored out from 20 to 40 thou.
So if you are looking at repowering a tired 4.3 or the gutless 5.0, my suggestion would be nothing less than a 5.7 carbed or MPI, with Vortec heads. The best horsepower bang for the block size and weight is the 6.2 MAG MPI rated at 350 crank/320 prop hp. The 5.0 weighs the same as a 5.7 or 6.2, but only puts out a whopping 220-230 hp; so why bother messing with it? Just my opinion.
The 6.2 as sold by Merc is designed for use with the Bravo drive only, and includes a belt driven seawater pump. If you are reusing your Alpha One/Gen II drive I suggest you remove this pump and its mounts, and use the impeller pump in the Alpha drive. This is how I am running mine and it runs cool. Switch to serpentine belt no 57-865615-004. That's the one used for Alpha configured V-8's with PS, but no belt driven pump.
You can run the water inlet hose straight from the inner transom plate fitting to the inlet of the PS cooler on the back of the engine stbd side, just below the distributor. Be careful not to kink the hose with too sharp of a bend.
If your engine has the 10 pin barrel electrical plug, that should mate up perfectly. Your gauges and alarms should all work fine.
One other thing: The 6.2 engine will come with a Bravo drive shift cable bracket. You will need to remove that and reuse your Alpha bracket. You will need a new interrupt switch which is an NC plunger style. You can't use the older style with the roller and metal blade, which is an NO switch. The switch has to be ordered separately.
The Bravo ECM does not recognize the Alpha interrupt signal to pause the ignition, so you have to wire the new NC interrupt switch directly to the coil driver circuit. Wire it in series into the pink/wht wire. This is just beside the coil on the back top port side of the engine.
If you don't do this the ignition will not interrupt properly, and shifting the drive out of gear will be a b*tch.
Pay attention to the max hp rating on the manufacturer's data plate in your boat, or the technical data sheet for the boat. You should not exceed the max rated hp, as your insurance company could take a walk in the event of an otherwise legit claim.
Just thought I would submit this for anyone who may be considering a repower engine package. The 6.2 MPI may be for you!
Cheers,
Rod
The 6.2 is rated at 350 crank/320 prop hp, whereas the 4.3 was rated at 180 hp; so a big, big performance difference. The 6.2 runs great and I now have over 90 hrs on it. Very happy with it so far. The cruise fuel consumption runs at about 4-4.5 GPH which is not much different than the 4.3 was.
The 6.2 is intended for use with Bravo drives only, but I decided to retain my Alpha Gen II drive. I changed the original 1.81 upper drive for a used 1.47 that I bought on ebay, and bolted it up to the original lower gear case, with a new water pump, naturally. Works just fine. I then sold my 1.81 upper unit on ebay.
The 6.2 came with a Bravo bellhousing, which bolts right up to the existing Alpha transom plate. Fortunately the Alpha and Bravo inner transom plates are the same part number. The Alpha driveshaft splines are the same as the Bravo and fit right into the Bravo coupler on the engine.
The original exhaust Y pipe would have fit the new exhaust elbows just fine, except I went with Hardin 40 degree side hull exhaust tips instead. I wanted to use Silent Choice exhaust selectors, but the fiberglass cowling behind the engine is too close, and they just would not fit. So I just blanked off the Y pipe.
The front motor mounts had to be moved ahead about 4-3/8" on the stringers. Drilled new holes and filled the old ones. No problem.
The 6.2 is about 4-1/2" longer overall than the 4.3. My engine bay had plenty of room in front of the 4.3, as the Mirage was originally offered with a 350 MPI engine option. Both the 4.3 and the 6.2 engines are the same width to the outside of the manifolds.
The 6.2 is about 1 inch higher to the top of the flame arrestor cover nut, and I had to raise the engine compartment cover somewhat to clear it. No big deal.
The 6.2 came with a standard Merc 10 pin electrical connector, which fit right up to the boat connector. All gauges work fine, including the alarm buzzer. The buzzer signals low oil pressure, high temp, low lube oil level, and low cooling water pressure, as well as “soft codes” detected by the ECM. I had to reset the selector on the back of my tach from 6 to 8 cylinder, no big deal.
As far as weight goes, I figure I did not add more than about 70 lbs net. I can't notice that the boat sits any lower in the water than before. All in all a great swap.
Any small block GM V-8 will work as a replacement for the 4.3. The 5.0, 5.7, and 6.2 are in fact all the same Gen I GM small block that originally started life as a 265 cu in V-8 in the 1955 Chevy. They have different bores and strokes, heads, cams, cranks, etc. The 4.3 is actually the same block as the 5.7; with two center cylinders missing. Both 4.3 and 5.7 have the same bore and stroke.
The 6.2 (383 cu in) is actually made by using a 5.7 block with the standard 4”; stroke, and a 3.75” stroke crank, as used in the 400 cu in small block Chevy car engine, way back when. Since this crank has a longer stroke than the 350’s 3.48”; the morphed engine is referred to by the slang term “stroker”. Since the block is re-used from a previous car or truck 350; it will have been bored out from 20 to 40 thou.
So if you are looking at repowering a tired 4.3 or the gutless 5.0, my suggestion would be nothing less than a 5.7 carbed or MPI, with Vortec heads. The best horsepower bang for the block size and weight is the 6.2 MAG MPI rated at 350 crank/320 prop hp. The 5.0 weighs the same as a 5.7 or 6.2, but only puts out a whopping 220-230 hp; so why bother messing with it? Just my opinion.
The 6.2 as sold by Merc is designed for use with the Bravo drive only, and includes a belt driven seawater pump. If you are reusing your Alpha One/Gen II drive I suggest you remove this pump and its mounts, and use the impeller pump in the Alpha drive. This is how I am running mine and it runs cool. Switch to serpentine belt no 57-865615-004. That's the one used for Alpha configured V-8's with PS, but no belt driven pump.
You can run the water inlet hose straight from the inner transom plate fitting to the inlet of the PS cooler on the back of the engine stbd side, just below the distributor. Be careful not to kink the hose with too sharp of a bend.
If your engine has the 10 pin barrel electrical plug, that should mate up perfectly. Your gauges and alarms should all work fine.
One other thing: The 6.2 engine will come with a Bravo drive shift cable bracket. You will need to remove that and reuse your Alpha bracket. You will need a new interrupt switch which is an NC plunger style. You can't use the older style with the roller and metal blade, which is an NO switch. The switch has to be ordered separately.
The Bravo ECM does not recognize the Alpha interrupt signal to pause the ignition, so you have to wire the new NC interrupt switch directly to the coil driver circuit. Wire it in series into the pink/wht wire. This is just beside the coil on the back top port side of the engine.
If you don't do this the ignition will not interrupt properly, and shifting the drive out of gear will be a b*tch.
Pay attention to the max hp rating on the manufacturer's data plate in your boat, or the technical data sheet for the boat. You should not exceed the max rated hp, as your insurance company could take a walk in the event of an otherwise legit claim.
Just thought I would submit this for anyone who may be considering a repower engine package. The 6.2 MPI may be for you!
Cheers,
Rod
