Hard exhaust seats or not?

[frederick_76]

I'v been told by some people to use the hard seats for the exhaust valves, and other people have told me that it is just a waste of time and money, that I dont need them. So... what do you guys think I should do??? Thanks, Fred.

[dwc43]

Never used them. And some of my cars are 20 and 30 years old and bone stock while others are to hot for the street or pure race cars.

[6 packin]

I agree with Dwc43!

I think its a waste of Money in a street car. Now if it was going into, wrecker of somthing that was going to do allot of towing, and squeezing 100,000 miles from maybe, but probably still wouldnt.

[MitchB]

Here's the deal... it's going to come down to how much heat you put into the exhaust valves and how hot they run. I receeded the seats on a SLANT SIX of all engines. I did this by running the engine borderline lean and with too much timing in an effort to squeeze out fuel mileage. No doubt, you can receed the valves on any almost engine if you aren't careful. Running relatively high loads for prolonged periods (extended high speeds) or faulty tuning at WOT will hurt the seats. Hardened seats will survive outside the safe operating zone and give you more room for error. but with careful tuning, you should be OK. Another thing you have to look at is the quality of the casting metal. Some heads have a thin surface hardening treatment with soft iron underlying this. The head on my slant was very tough and hard to cut, indicating a good casting. We had such a tuff time cutting the seats for the first two inserts that we just didn't bother installing the other four.

Mitch

[ehostler]

Running stainless exhaust valves is another way around the hardened seats.

[MitchB]

Running stainless exhaust valves is another way around the hardened seats.

This won't help because while the valve itself will be able to survive higher temperatures, it is in the head where the seat is located where the recession takes place.

Mitch

[ehostler]

right and wrong...

In a standard head, the recession of the exhaust valves is caused by small amounts of the seat sticking to the back of the valve. Over time, you remove enough of the seat that the valve receedes. The seat is not compacting or moving anywhere. A hardened seat prevents this from happening. The iron of the exhaust seat will not stick to the back of a stainless exhaust valve.

[MitchB]

Regardless, if the seat runs hot enough, you will change the local properites of the metal. Believe it or not, the modular engine used in the Ford Cobra (32 valve) has a design flaw identified by Rousch engineers. The exhaust seats in #1 & #7 receed due to cooling/design problems and this engine uses stainless alloy valves and valve seat inserts. The exhaust valves used in most OEM applications are a stainless alloy of EV-8. Stainless valves by themselves will not stop recession.

Mitch

[dave571]

What kind of heads frederick 76?

73 and newer heads already have hardened seats. Won't need to put in inserts, unless you're going to bigger valves

[frederick_76]

I know that they rae "J" heads and they have 2.02 in them now. But cant find any other numbers anywhere on the heads? I did have the Seats redone earlyer this year. Heads are still off the 360 (its not done yet).

[ehostler]

Hey Mitch, you said it yourself if the seat runs hot enough. You would have to have a terrible out of tune MOPAR to run hot enough for the stainless exhaust valve to not resolve the problem.

[perfmachst]

hello, I do cylinder head work in my machine shop. now, lets
figure out this exh seat thing. the OEM specs were for an
interference angle on the seats (int & exh) . when unleaded gas
came out, exh seats suffered. when a seat does recede, it is the valve that cups first, which then pounds out the seat in the head.
detroit went to stainless exh valves to prevent this from happening. then the after market brought out hard seats for the older heads. you can use the stainless valves on OEM seats and they will live just fine. valve face and valve seat angles have to be changed. now a 45 deg on seat and valve will prevent seat pounding out. of course, tuning and jetting , temperture will affect any valve life. for every day use this combo works. hope this helps,

[frederick_76]

Well I went with the stanless valves a while ago, so I dont think Ill have the heads fitted with the harden seats. Thanks!