I have a 1998 3000SCR, the twin Mercruiser 5.0L finally got to tired. I am upgrading to 5.7L Vortecs. I have the Thunderbolt ignition, with the Mercruiser ICM and Knock Sensor. What I have not been able to find information on is will the 5.0L ICM work with the 5.7L engines. As it looks like Mercruiser has discontinued the ICM's. And they are quite pricy if I could find them.
It will work as both engines are GM small block but I think the timing advance curves are slightly different between the two. If you went with a aftermarket distributor it would be the same for either application. You can always reach out to Mercruiser help and ask them.
Engine Upgrade Questions
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