this is a 454 gen 5 based engine with the mercruiser weind 177 supercharger and mercruiser dominator carburetor. Runs good but wont turn over 5000 rpm no matter what we do to it. Totally changed ignition to a msd hei distributor. New fuel filter, fuel pump. changed prop to lower pitch, still turns 5000 rpm. Any input on this?

how fresh is the engine ? blower could be worn, valve springs, cam going away ? what flame arresters ? have you done a compression test ?

I had a pair of the Merc 525 SC's years back and they ran at 5400, right under the rev limit. The point here being maybe you should make sure the ignition system is in fact the real Merc items for the 525 SC and not something other. If I remember right the rev limiter was a separate component, might not be right one. There have been some big block Merc motors that were set with 5000 limits.

What Gen V 454 engine???? What are the specs??? Comp ratio, cam, heads????? How many lbs of boost????

Did you resolve this issue?

Merc Racing spec on this was 4800 - 5200 rpms for the 525 SC - OEM stock.

Make sure throttle plates opening up to full advancement at WOT..

Check all ignition related parts & outputs,

try another brand of lower prop pitches,

compression test # s and leak down percentages - what are they.

What are the fuel pressures at all rpm ranges - especially at WOT?

Is the bottom of your hull spotless and damage free and the same goes for the outdrive.

Hull / boat carrying any extra weight compared to years past ? Water saturated, gear, passengers and so on.