7.4 mpi with 454 mag cam question
 

7.4mpi rebuild threw in a mag roller cam and springs. stock exh through Y pipe. no exhaust bellows to drive. I have pulled the exh and had the surfaces checked flat/ pressure tested no leaks. Leak down check done, no problems.
Now the problem, is this mod prone to water reversion? I am getting some water at idle, but not enough to affect how the engine runs. Any ideas? idle is currently at 750rpm

What are the cam specs? For the time being bump your idle a little. Did you notice any diff in the performance with the cam change.

the motor is in a cruiser, was looking for some more at 3k and got it. The boat gets on plane way better and picked up 300rpm on top to boot. I am way happy with the torque increase. Working with Mark at Precision for the ecu and he has been great. I just have this water issue.

the cam
MERCRUISER # 431-850478
.004 300*/ 300*
.006 288*/288*
.050” 224*/224*
.200” 125*/125*
Lift .483”/. 483”
ICL 109*
LSA 115.5*

The stock magnum cam should not revert any water. Its possible that the cam may not have been degreed in properly.

I did double check that last year. I am starting to wonder if maybe I was sent the wrong cam by the guy that sold it to me.