I recently purchased a 67 Firebird that someone swapped a 428 into. I just changed the oil, but I am having a hard time figuring out how much oil to put back in. The dipstick appears to be aftermarket and I don't trust it. The oil pan is the original style with the drain plug off to the side. After putting in only 4.5 quarts, the dipstick shows full. Considering I changed the filter as well I was thinking it SHOULD take 5 quarts plus a bit more for the filter change. I went ahead and added 5 full quarts and now it's showing passed the full line on the dip stick.

Is it possible I didn't get all of the old oil out? The oil wasn't very warm when I changed it due to the proximity of the oil filter to the headers. I had to let it cool off some.

Should I add another half a quart to be safe? There is so much conflicting information about the actual quantity needed for this engine.

5 quarts
even with 4 1/2 you will be fine as long as your not revving the engine to 6000 RPM for 2 minutes.

I have always done six quarts with a large oil filter change. That is what was recommended by the factory for 326-455.

All of the Pontiac V-8s use the same oil pan. They take 6 quarts with a new filter. You need to run the engine so the oil gets into the filter and all the galleries. Let it drain back and then check the level. You may have the wrong dipstick. Another problem I have seen is that when someone does work on the engine, they forget to put the lower dipstick tube guide back. It bolts to a main bearing cap and guides the stick away from the crank shaft. Without it, the stick hits the crank. Then they use a shorter dipstick, solving that problem, and creating another.

Just don't add too much. High oil level causes foaming and will do damage to your engine. Safer to be a little low than a little high