A holley hp efi was installed, limiter was set to 6300, hard limiter set to 6500 (yes very built engine) Engine will not spin past 5150.
Nordic Heat built 496 540 pro charged and make max hp at 6300.

I am thinking something left over form the old ecm or smart craft system is keeping it from moving past 5150.

Did you make a prop change at the same time?

What ignition? Spark plug gap?

do you have 8 coils or another ignition control that is wired to the single coil?
That side car ignition control could have you limited to 5150

we found this, spark plugs are gapped to .060 should be .035, airfilter is too small and engine is collapsing it. I was told to run my LS style coils and see if i have one out. All that could lead to the problems. We run an Holley HP efi system on a LS based ignition.

Gap pulled to .045 and BAM rpm

Good news !

Maybe the 496/8.1L crowd will listen to me now (staying with the dumb OE spec of .060") and stop burning out their wires and coils. Someday maybe. One day closer ? LOL.

Again, great move on your part and thanks for letting us know.

Noted... I'm getting ready to change the plugs on my 496 2500 Avalanche.