honestly I think that hardened seat are a good idea in just about anything, the really do last alot longer than the regular ones and are even more needed if running unleaded gas seeing as the lead isn't there to cusion the valve on the seat
Here's what he has to say about hardened seats... Oh, by the way, my heads spent 8-9 years on the mustang WITHOUT hardened seats, and have had no problems with seat recession. The only way to cause seat recession is to run a head under a CONTINUOUS high load... such as extreme towing up and down hills. The average hotrod won't have any problems. If you're still paranoid, add a splash of av-gas to the tank every now and then for a little lead content. (and octane boost)
-> My question is about hardened valve seats, I have put them
-> in the past rebuilds I have done, but since then I heard
-> some people say that they weren't nessecary. I learned they
Inserted seats are for repair. They interfere with heat flow from the valve; the ports have to be ground to blend the seat in; improper installation (can you tell with your naked eye?) will let them come loose, with potential for catastrophe. The cutting necessary to install the seats weakens the head and can promote cracking, particularly if the head is subjected to higher than stock pressures or heat, ie a high performance engine.
You want inserted seats about as badly as you want a veneral disease.
Most shops call them "hardened" seats; most inserts are plain old cast iron, like they just carved out of your heads. True hard seats are Stellite and they cost over $10 each, and they're righteous bastards to cut a seat on.
I'd never put those insert seats in my heads unless it was absolutely necessary. Ever seen what happens when one of them decided to come loose and drop? I've had a few 460's and 462 Lincoln engines apart and I've never had one the seats were recessed in, and they ran fine on unleaded fuel for years. Just add some additive and it'll be fine. All the leaded fuel did was lubricate the seats.