5.0 to 5.7 ECM compatability

[Kodiak2359]

I recently purchased a 2004 Trophy pro which originally came with a mercruiser 5.0. The previous owner had a gm new 5.7 long block installed this year but the ECM 555 was not changed.

I have read that it won't matter all the way to it will destroy the engine so I would like to know if the ECM absolutely needs to be changed or reflashed or if it would just be a slight performance advantage.
I use the boat for fishing not racing or water sports. It seems to run great as is but I don't want to snap my valves off either.

Thanks for any input

 

[Scott Danforth]

just get it re-flashed. the 5.0 and 5.7 use different fuel mapping, so the motor in your boat is probably running a bit lean.

 

[alldodge]

You need a 5.7 ECM, the computer will not supply enough fuel through out the rpm range.

Some have said the 555 can be reflashed, but so far I have not seen it done successfully.