Misfire small block.
 

408 Small block the number one cylinder is misfiring i did a pressure check and it came back the within 10 percent of the others at 150psi, i changed the plug and wires and it is still missing. I could use any help at this point before i tear it down. Its has 9:0-1:0 pistons and RPM Performer Heads.

duster -

Did you actually check for spark at the plug?

Not a lot it could be if it's a real misfire. Plugs, wire, distributor cap, distributor, control box (if you're using one). Don't over look arcing. Run the motor in the dark and see if any sparks are flying.

You're sure you didn't cross any wires, right?

A random misfire can also be an alternator or regulator.

Archer

Does it miss at idle ? Under load ??? You have checked the usual things.
could be a bad valve spring ?

The heads and valve springs are new, i took the valve covers off and no issue was found. I tried a different set of plug wires i had and it still doesnt fire at idol or under slight load.

Did you pull off cap and check how the rotor is striking -I had a similar issue with my 408 and it ended up being a burned up rotor due to a cheap aftermarket cap that didnt sit flat on the dist. also make sure you check to spark plug