i have an xe268h comp cams cam and i used a stock timing chain and in the directions of the cam it sais i should use a comp cams timing chain because the stock chain sometimes retards the timing. so now i am installing a cutout and new oilpan gasket and timing cover and electric cooling fan so i figured it would be the best time to put a comp timing chain on if i needed to. thanks alot

You should definitely not use a stock one.

Starting in about 71, GM decided to change their timing sets to set the cam 4° retarded from where it had been before. However, aftermarket and replacement ones, stayed exactly like they were. So if you use a stock timing set, the cam will be retarded 4° from where it's supposed to be. That whole issue is the source of all the confusion about cams being ground with "4° of advance"; all that means, is that they're the same as a stock cam with an early-model or replacement timing set. I think nowadays we can safely leave "early-model" out of that equation, since all of those are 35 years old or more, and have probably long since either worn totally out or been replaced.

It doesn't have to be a Comp one; but use a good quality one from a reputable source; use either a Link-Belt (stock type) chain, or a "true roller" type chain. NOT a cheap "roller", aka "truck chain", "split roller", etc. Those are not rollers at all, but rather bushings, and they wear ("stretch") worse by far than the Link-Belt type.

Now there's something I never knew! Why on earth did they retard the timing sets 4 degrees?? Emissions??

Yup, emissions. Instant free EGR and lowered combustion pressure (lower NOx in both cases), with no extra moving parts.

would a comp cams magnum timing chain work? my cam is an extreme energy cam not a magnum so i wasnt sure.

also forgot to ask, the magnum is a double roller chain so do i need a different timing cover or dowel pin for the cam or anything like that?

So if factory chains were retarded for emissions, will new timing chains make the car less emissions friendly?