fuel pressure dropping over time

diymirage said

Good point

It made 420 and change on the builders dyno

So your thinking is that even when it's clean it will restrict fuel flow?

I can see that, at full bore, but the pressure drop in seeing is during regular traffic

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I don't recall you saying if it has ever worked properly. I would bypass or open up the regulator and give it a whirl. My son had a similar problem where his truck with a 360 would fall on its face after getting into it. We found the fuel pump was bad & after replacing it all is good again. When we took the pump out, the pump arm had slop in it.