Questions about 1998 Gen VI 454 Mag MPI?
 

1. What is the spec HP of the 1998 GenVI 454 Mag MPI?
2. Was the orginal 525SC a 454 Mag with a Whipple charger?
3. What is the HP increase on a stock 1998 Gen VI 454 Mag MPI adding a Stainless Marine or EMI exhaust system?
4. Is the 1998 Gen VI 454 Mag MPI a roller valve train engine?
5. Are the heads on these motors decent or are they fairly restrictive?

1. 385 HP.

2. No. 454 Mag bottom end, low compression pistons, Crane flat tappet hyd cam and valve train components with the gold roller rockers, GM rectangular port heads with upgraded 1.88 /2.25 valves, Weiand 177 ci blower with a 1050 Dominator, and Gil manifolds. Super running motors, had a pair in my last boat and they performed flawlessly for six seasons and three seasons later are still going strong. Mine had super chillers added and the boost upped from 5 to 7 lbs. and I installed the CMI elbow tops. Mine dynoed over 600 hp, wish I still had them today.

3. My guess would be 20 - 30 hp.

4. I believe the Mag MPI's are a hyd roller set up, might be wrong on this.

5. The Mag MPI's use the same GM rect port heads as the rest of the Merc big blocks. Only the 300/330 hp low perf 454's used the smaller oval port heads.

Hope this helps! :D

Thank you for the info, RaggedEdge.