Hardened Seats...beaten to death.

Discussion in 'The Bench' started by Electra-fied, Jan 19, 2020.

  1. Electra-fied

    Electra-fied GR8WHTE

    I know this conversation has happened before, but I still want to hear it again....

    I have 1970 "SF" 455 heads. I start the valve jobs this week. Car is driven about 5000 miles from May until the snow falls and they coat the roads in salt in November. However, we are moving west to a fair weather state where it will be possible for the car to see about 9000 miles annually. I do plan on keeping the car for the duration. That being said....

    I am building a motor that is going to be peppy, but won't require me to use more than 87 octane. That's how I want it. So....do i spend the extra time putting in hardened seats, or do I trust that the heads are solid enough that its not worth the money. I am a bit heavy footed but I'm not NASCAR/drag racing the thing. Nor am I "granny" driving it. I do tow a 2500lb trailer from time to time, and it may even get a bigger trailer behind it when we move from Minnesota to the West Coast.

    So lets here those pros and cons!
     
  2. No Lift

    No Lift Platinum Level Contributor

    If you said you only planned on 5-10,000 miles total for the rest of your ownership I'd say hardened not necessary. If you say 5000 a year and possibly more with potential towing spending the money on hardened seats is a no brainer. If you want to be wondering how the seats are holding up after 20-30,000 miles save a few hundred now. Other than the extra cost there is no con that I know of. Have them do a good 3 angle valve job and backcut the valves to pick up a few HP while you are at it.
     
  3. jmos4

    jmos4 Well-Known Member

    Hi,

    If you're worried about using 87 octane you need to lower the compression ratio. 1970 compression was over 10 to 1.

    Hardened valve seats are for unleaded gas, and even if you run unleaded on the stock valve seats it only will mean you might need to do a valve job sooner.

    Regards,
     
  4. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I can tell you the exhaust valves on my 430 heads sunk after 1 season of summer driving back in the day. I've got hardened seats in that now.
     
    BUICKRAT likes this.
  5. Electra-fied

    Electra-fied GR8WHTE

    Ok...hardened seats it is. Thanks for pushing me over the fence. :)
     
  6. Electra-fied

    Electra-fied GR8WHTE

    I'm planning on keeping the 76 motor, but just replacing the heads and rejetting the Rochester. That will give me the added snort I'm looking for but still keep under 10:1 for the 87 octane. Should be a nice build that makes me happy and doesn't scare the wife when she drives it.
     
  7. No Lift

    No Lift Platinum Level Contributor

    Even swapping the '70 heads onto the '76 shortblock will only get you into the 8.5:1 area. Have them mill about .030" off the heads. that will get you closer to 9:1 which will still work great with 87 oct.
     
  8. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Just make sure you at least run mid-grade 89 octane when you're towing, that extra load can cause detonation. That's why truck engines will usually have lower compression from the factory back in the day.
     
  9. Electra-fied

    Electra-fied GR8WHTE

    .030"...that's about the thickness of a credit card, right? I take it there's plenty room still to make sure valves or spark plugs don't get smacked by the pistons?(rookie questions, sorry). The heads are being rebuilt to factory spec, no stainless valves or anything special other than hardened seats.
     

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