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71 Blazer with 78 heads?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Dave_S, Jun 3, 2001.

  1. Dave_S

    Dave_S Registered Member

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    I have a problem that has sidelined my 71 Blazer. A stud for the alternator bracket in the head has broken out taking a chunk of the head with it. Basically, I have to get a new head.

    I've found a site with reasonable prices for heads, but they only have as late as a 78 head for a 350. I'm assuming that this isn't too much different than a 71 head with the exception that they don't need "leaded" gas?

    Dave
     
  2. arq

    arq 1/2 ton status

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    you won't notice the difference, the advantage will be the hardened seats for unleaded gas. just make sure the combustion chamber on the head is the same size as the other(if you are only changing one). If you are upgrading both(recommeded) don't worry about it.

    ARQ.

    1-72 4x4 CST Blazer
    2-71 4x4 CST Blazer
     
  3. 2quicK5

    2quicK5 Registered Member

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    '71-'85 350 heads have either 74cc or 76 cc combustion chambers. '71 and up use induction hardened valve seats for use with unleaded fuels and have 14mm tapered spark plug seats. Many '75 and up (305, 350, and 400) castings are 'thin wall' castings made to save weight. Avoid these as they are known and prone to form cracks around the exhaust seat and they warp rather easily also (casting numbers 333882 and 462624). They can be noticed by the large exhaust heat riser ports that connect internally to both center exhaust ports and they have tapered intake ports. The GM target master replacement 350 crate engines get the good early '70s design heavy wall castings (casting #s 3973487, 3973493, 3998993, 330545, 3998920, and 3998997). These heads all have 1.94" intake and 1.50" exhaust valves like your '71s. Stay away from 262, 267, and 305 cid heads and heads with 1.72" intake valves.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" springs, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph<P ID="edit"><FONT SIZE=-1>Edited by 2quicK5 on 06/05/01 07:57 AM (server time).</FONT></P>
     

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