Ultra copper RTV. Works like a champ.

 

When I did mine last year I used the ARP sealer on the lowers with ARP moly on the top and haven't had any problems. My car is my daily driver and has been to Tennessee and back twice sine then. I think the important part no matter which one you use is to make sure you get the sealer pushed into the threads of the bolts to insure a good seal.

 

I've only used the ARP thread sealer -- they know a thing or two about fasteners and how to lubricate/seal the threads. You should never use rtv to seal threads -- getting the female threads clean again is next to impossible once the rtv is in there.

BTW - teflon tape isn't a sealer; it's a lubricant. It's designed to lubricate tapered threads (plumbing) to allow the fitting to be tightened to the point where the threads do the sealing without having to put as much torque on them.

 

I've used the ARP stuff twice on 2 different blocks and haven't had a problem

 

I go with ARP, but mainly because it's readily available

 

Thanks guys! I'm excited. After 9 years of owning this beast, I'm actually ready to bolt on the heads. Maybe in the next century, I can put on the intake! The guy I talked to at ARP emphasized to make sure the threads in the block are really clean and he said to take the sealer and the moly and work it down into the threads of the block as well as the bolts themselves. He also said to make sure to clean the bolts good becaus they come with a protective oil on them that will prevent them from making a good seal with the sealer.

 

I use the non hardening permatex stuff.....has always worked for me