Here is a long explanation of what I got, I hope someone has some simple suggestions.

Had a well running 350 with a TH400 automatic until a wide open short pass. After the pass, I heard a clacking noise, slowed down and started listenening to it. It eventually got louder and sounded like it was coming from the firewall area. I made it home and parked it in the garage thinking the worst. I took off valve covers and checked all valves, they all seem to be adjusted properly and in working order when the engime is turned over. There is nothing obvious out of place. I started the car again and it fired right up, but the noise was still there. After listening closely it sounds like something hitting metal, like the oil pan possibly. It is hard to isolate where the noise is, but I would say somewhere in the flywheel area, but definatley down low on the bottom end. The noise is consistent but not to fast. It does go faster when the rpms are increased.The trans shifted fine and I still have all gears. The engine sounds fine and does not miss at all, it starts right away and does not sound bad except for intermittent clacking.

What are some things to look for? Could something be hitting in the oil pan while the engine still runs good? Could it be something with the flywheel or torque convertor?

I don't think it is a flattened cam I have been through that before. This sounds different.

What did the oil pressure do? I suspect you spun a rod bearing.

Exactly, where is the oil pressure? Drain the oil and take a look inside the oil filter if nothing is obvious.

I forgot to mention I still have good oil pressure, and that did not seem to be affected.

I have not looked at the oil yet, will do that this weekend. If a bearing is spun will that be obvious in the oil? Does a spun bearing make a loud noise?

Thanks for the replies.

I would check the fly wheel, make sure no cracks and bolts are tight.

I use a piece of 3/8" rubber hose with one end to my ear and poke the other into the valve covers etc to better pin point where it's coming from. You can also use a pry bar etc with one end to your ear and the other on the head/block.

You blew a header gasket.

You blew a header gasket.
Good thought, sometimes that can sure sound like a metalic sound.

The dreaded spun rod bearing. Cross your fingers.

Diagnose a spin rod bearing by pulling off, one at a time, a spark plug wire to each cylinder.
When the noise changes, the faulty cylinder has been found.
Like JimM suggests, I'd check for a blown exhaust gasket.

Diagnose a spin rod bearing by pulling off, one at a time, a spark plug wire to each cylinder.
When the noise changes, the faulty cylinder has been found.
Like JimM suggests, I'd check for a blown exhaust gasket.yes sir x2:yes:

Sounds like you cracked the flywheel.

It would of lost oil pressure if he spun a bearing.

Hopefully you didn't spin a rod bearing. If the torque convertor bolts become loose or break it'll sound like it's about to throw a rod.

First place I would look is under the dust cover for cracked flywheel or loose bolts. Could be torque converter or front pump.

check your bell housing area out first. fly wheel bolts torque bolts that fun stuff.......if there is no loss of oil pressure rod bearing is unlikely

This was posted a long while ago, but the diagnosis may be helpful to someone else in the future. I just tore down the engine and found that the #4 rod bearing was toasted. It was about time for an update on my engine anyway, so this allowed me to get a new 383. Car was down for a bit but it is going strong again. I read a lot of post on this site to complete the build and install myself, so I know how helpful these updates can be. Thanks everyone.

Congrats on the new accomplishment.
Now enjoy your labor you put into it by driving it.

I figured it was flywheel or bearing. The trick now is to find out why the bearing spun.

Drain the oil, look for shiny metal particles in it. Sounds like rod knock to me.