I have a firend that has just bought a 79 TA with a 67 400ci bored 30/over.It would back fire and pop we have found that the cam had lost a lobe.Ok did it have to much lift, the cam is a 233/540, the roller rockers are 1.65, the push rods are 9in.Is this to much lift for the cam because when it was removed it had lost 3 lobes and the lifters had concaved?Now we are trying to find out the best cam for the rollers and push rods he wants to make it like a RA we will change the push rods if needed but keep the roller rockers.The heads are 670 the best what do you guys think???  

Did you replace the valve springs? The factory springs will bind for any cam with much more than factory lift or more than 1.5:1 ratio rocker arms.

If you have the correct springs I'd check to see if the pushrods are binding in the cylinder heads with those 1.65 rockers. You can verify by removing a valve cover and cranking the engine with the ignition wire disconnected from the HEI. If you check, and they bind, the pushrod holes in the heads need to be elongated with a file or rotary grinder. (You need to pull the heads to do this)

The Comp Cams XE268H is a really good cam for the 400, along with an Edelbrock Performer RPM intake manifold, headers and properly jetted carburetor, you'll have a very fast combo. The XE262H works well too and gives a better idle if you're running an automatic trans and have power brakes.

During cam install, use the assembly lube that comes with your new cam. Be sure to properly break-in your new cam and lifters at 2500 RPM for 20 minutes following installation to make sure the lifters and lobes seat to each other properly and the cam will have a much longer service life.

Today's engine oils have the extreme wear additives removed to extend catalytic converter life. I use STP oil treatment with each oil change to restore these missing additives. Or, you can also use Shell Rotella Diesel oil, which still has the wear additives in it, since diesels don't use cat's.

Hope this helps!

Kevin