I ran compression on 74 225 valiant all are 160psi, ran on my 65 Dart 225 and got 150 on 5 cyl and 140 on one is it time for a rebuild,Also engine on dart sucks for power. Both are automatic.

Both of them are within spec. I'd first check the timing and give it a good tuneup.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Check the valve lash as part of the tune-up. (valve adjustment)
Tight lash will throw-off your cranking compression readings.
DD

Even if you can't get it any better than that, those are all pretty high numbers. I'd leave it alone until something breaks.