I attached a video of the sound the engine makes on idle. It kind of makes a sound like those old muscle cars. Maybe an exhaust leak? It sounds louder from underneath the car and the drivers side. I also have a pending code for oxygen sensor circuit malfunction, but for the opposite side pre cat sensor. It remained after replacing the O2 sensor, but is pending now instead of confirmed. I tightened the exhaust manifold to head bolts, but I'm not sure if it made a difference in the noise. What could be causing the noise? It has made this ever since the engine rebuild that I have recently done.

 

The "lopey idle" sound in the old muscle cars is caused by valve overlap. My discovery makes a sound at idle that seems kindof similar, but much less prominent. It also is quieter as the car warms. When I rebuilt the engine, I replaced one of the heads, It was at or maybe a little outside the tolerance for the amount of material you can take off the head when resurfacing. In theory this would make the valves stay open longer and may create valve overlap. It also seems this sound is louder on (or coming from) the side of the replaced head. Is this what is happening? Would this cause anything bad to happen?

 

Just an exhaust leak, do the leaf blower/show vac test.

 

About resurfacing the head, there is a simple way to re-adjust the valves to get back in spec. Insert shims under the rocker shaft pillars, equal to the amount taken off of the head. The shims need to be the correct shape in order to work with the oil passages. Not sure who sells them, try Rovers North maybe. Not installing the shims can cause problems if the lifters are compressed during all four strokes.

 

I got the fancy remflex gaskets extinct recommended. Would it be bad to put rtv on it as well?

 

Not really needed but a thin coat would not hurt anything