hardened exhaust seats

[bouncer]

If I cut my valves .1" to 1.6 exhaust and 1.88 intake, will I need new hardened exhaust seats, or will the metal still be there? Also, the purpose of using a 11/32" diameter valve stem over a 3/8" valve stem is? Just more room to flow?

[dave571]

Your question is a little vague.

What heads do you have? What is your application.

Mopar cylinder heads had induction hardened valve seats from 1973 on.

If you're installing larger size valves, that hardening is lost. If the car doesn't see a lot of miles, you won't need to have hardened inserts installed.

If is does get a lot of miles, than hardened seats are recommended.

I not sure of the benefit of larger stem size, but I'm sure someone here does.

[rumblefish360]

Years ago, larger valve stems were stronger. Today, the thinner units can be just as durable if not more. Yes, the idea is flow. Every little bit helps.
You will lose the harden seat area if you go from 1.88 to 2.02. Just doing a valve job won't take the hardened area away.
New seats are in the MoPar book as well as other sourses.

[DartGT66]

Actually, the main reason for the smaller stem diameter of the valves is not the flow; small changes inthe stem diameter does not affect it noticably, it's the weight.

[biggerhammer]

the intake seats are not hardened as they pull in cool air, the exhaust seats are hardened, and if you just cut them bigger from 1.5 to 1.6, it would be best if you had hardened inserts installed at that time. you still need to let us know which heads as some are induction-hardened and the hardening can go out to that size.

[kdoghouse]

As was previously stated only the exhaust seats are hardened. The difference between 1.6 and 1.5 valves is .100"- but that is only .050" per side. You wont leave the hard areas. Plus the hardened seats are usually around .125" deep.

Hardened exhaust seats are needed on engines that are loaded on a regular basis such as tow vehicles, boats and so on. On regular vehicles there wont be a problem. I do recommend stainless valves though.

The reason for smaller diameter stems is both weight and flow. That is why valve manufactures make under cut stems, for better flow.

[bouncer]

Sorry for the delay, been busy an such. Heads are from 77 era. I talked with the machine shop, said I probably wont need too, but I'll see, thanks guys.