410 LA small block will not rev past 6000

I didn’t catch the 4 speed info.

I re-read the OP.

I built this motor about 7 years ago and it has never wanted to rev past 6000rpm……….

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falls on its face at 6000 rpm.
Attached is the Dyno Chart, you can see it droppes off hard like it's hitting a rev limiter.

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It would seem as though since it’s been together for 7 years……he’d have a pretty good handle on the engines behavior.

I don’t know what it is, but I’m quite confident it’s not anything to do with the head flow on his build.