Hello All,

I have done a search and have not found much on this subject.

Currently I have a 2006 Baja 20 ft bow rider with a 5.0L MPI Alpha motor. Boat does 60 mph on a speedo not GPS.

Last year I found my risers were bad. Engine had about a quart of water in it and it milk shaked. The cylinders are ok but you can see some pits from where the water sat over the winter.

I plan on building another engine.

I would like to go 350 5.7L. 088 Casting block, rebuild it with marine bearings and gaskets, brass freeze plugs etc. Heads will be vortec iron heads (not sure on casting numbers yet). I would also like to put a comp cams extreme marine 270 roller cam in it. Forged flat top pistons. Basically a mild 350/355 with a nice sounding cam and hopefully around 300-350 HP. My drive should handle this just fine since I have a small boat.

1. Will my current 5.0L MPI system work with a new cam, flat top pistons etc? I know it will bolt on, just need to know if I need to reprogram the computer.
2. Does my motor have a cam sensor? I think it has a crank sensor. Will This stuff switch or not.

Thanks for the help.

Not trying to reinvent the wheel here or anything

Ayuh,..... Forged is unnecessary, hyperutectic is the way to go,....

'n flat-tops are Not what works best with the Vortec heads,.....
The block should be decked to give 'bout .040" 'tween the pistons, 'n head,.... the Quench area,....
To get the quench factor, 'n to keep the compression ratio at or below 10:1, ya need inverted dome, or D-dished pistons,.....
The inverted domes, or D-dish pistons mirror the flat spot on the heads, which is what creates the massive torque available,.....

'n while I don't do 'puter controlled motors,....
I Do know the original 'puter will Not work properly with a "Built" motor,....
It'll need to be replaced, or remapped to drive the Mpi,....

The current MPI will work with the new motor, but it will need some tuning. Not a lot, but some. Your 'new' motor will likely start and idle on the stock tune which would be a good baseline starting point. You might need to go with a bigger injector depending on the size injector you have now. We'd need details to advise further. You would have to install a wide band O2 sensor to get AFR numbers. Easy to do but a MUST HAVE for tuning.

Serial number of original motor and MEFI controller would help steer the conversation on which way to go.

from OEM Merc stock would not be a MEFI control engine - Merc started ECM 555 in 2002 and PCM 555 2001.

OP should have an ecm 555.

for the OP app the out drive gear ratio if I recall correctly is different.

tuning a ECM 555 is not easy and there is only about 2 people able to but prob would pass on the deal as a guess on my part.. And that recal of the ECM would be thru the mail. Not a good way to recal a change over engine especially with bigger displacement. .

not all internal parts from a 5.0 will interchange with a 5.7.

Serial number is OW353xxx

Alpha ratio is 1:62?

No 5.0L interals will be used all 5.7L internals

Is there another ECM that could be used for this application that is more user/budget friendly?

Isnt the ECM 555 used for big blocks also?

HP 500 EFI used MEFI 3 - but the 496 used PCM 555 --- 2001 and up to 2010 NON catalyst engine. ECM 555 is not the same as PCM 555. They can not be interchanged from small block to the big block.

2008 thru 2010 CAT 496 used PCM 09 this was not a motorola 555 - its a Visteon based controller

5.7 MPI ECM 555 standard gear ratio was 1.50 for alpha outdrive.

I doubt anyone would recal your ecm 555 -- 5.0 mpi to a moded 5.7 MPI. They most likely would not stand behind the recal if something was to happened to newly moded 5.7. and I would not do a retune thru the mail for sure in this case.

1) You could go with a carb (I wouldn't but that's me)

2) There are several ECMs you could use. You could use anything from a MEFI 1 thru MEFI 4. It will take some work.

3) Several aftermarket options. Holley gets many positive reviews. I highly suggest immersing yourself in EFI knowledge to help with your decision making process. There is a substantial outlay of cash when getting a different EFI system. But, once you have it you can use it on anything.

4) The 555 controller is not easily modified thus it ties your hands. The MEFI, Holley and other aftermarket EFI units are all tune-able. The stock 555 will likely run the 5.7 at idle on a test stand. I don't recommend doing that for long term however.

5) You could simply rebuild the 5.0 with a .030" over bore, stock cam and heads and use your existing EFI. Don't expect any power increase. The extra 4 cubic inches will not affect the stock tune.

IF you had a pre 555 controller motor (i.e. with any of the MEFI units) your problem would be much simpler.

Adding a supercharger is way more work. To do a blower right requires changes from top to bottom, and again you are hamstrung by the lack of readily available 555 tuning.

have you considered getting a 4.8L/5.3L LS or a 6.0L from a wrecked truck/suv. most cases you can get a running motor with wiring harness and ECU pretty cheap ($400-$1,000). the biggest adder IMO is the exhaust manifolds ($1,300). bell houses bolt up except for 1 bolt. tuning options are pretty open ~$99 for an EFI live seat. 3bolt-4 bolt adapter are all over the place. 6 bolt mains, lighter motors

IMO there is no reason to build a SBC other that nostalgic builds. The LS is just better all around. I'm looking to go from a 5.7L SBC to a 4.8L/5.3L LS for my boat, the 4.8L makes more power (HP + TQ) than my current motor and is pretty close to the TQ limits of a merc Alpha/OMC cobra off the line (EFI gets you TQ limiting to protect things).

I would do a 350 HO Mag drop in engine from Merc reman and thats the highest one can go with the alpha. But your gear ratio is wrong as well for the standard ratio using anything bigger than your 5.0 mpi..

ECM 555 --- the HVS on 5.7 and the 6.2 down the road ended up using the cam sensor in the HVS. the first couple of years they did not use the cam sensor in the HVS. The crank sensor was used from the start on the ECM 555 4.3L the 5..0 L the 5.7 L and the 6.2 L MPI engines. With said the crank and cam sensor and the HVS can not be used with MEFI 1 - MEFI 2 and MEFI 3 . There is more info as well like MEFI 1 thru 3 was bank / batch fire of the injectors and so forth.