71 Ls3 cylinder head question

Discussion in 'VIN, Trim Tag & Drivetrain Decoding' started by Jwross79, Apr 16, 2017.

  1. Jwross79

    Jwross79 New Member

    Apr 16, 2017
    I have just purchased a 71 rs/ss ls3 project car and have been spending the better part of a week decoding the car and I am hoping someone can help me with a cylinder head question;
    Car is an 02c Feburary 1971 build
    Block is CLA vin matching block along with intake carb dist. Etc....
    Head castings are 3964291 (1970) 375hp heads with a November 1970 casting date

    Question is----can these be the correct heads for the car? All of my research shows those castings as 69-70 only pre-emission heads and all 71 camaros had the 300hp castings.
  2. 70 SS/L78

    70 SS/L78 Veteran Member Lifetime Gold Member

    May 5, 2005
    Rockford, MN
    The 291 heads are not correct for your car. Actually by November 1970 Chevrolet wasn't producing any engines that used the 291 square port heads... except for a handful of 1971 LS6 Corvettes. Good news is the 291 heads are worth more than the ones you actually need.
    I don't have my book to look at right now and not sure if the 71 LS3 used the 6272292 heads or something different.
    Most likely the heads you have are an over the counter replacement.
  3. mech393

    mech393 Veteran Member

    Aug 9, 2003
    belvidere illinois usa
    I have a 71 Camaro and my heads are the 820 number heads which is correct for the 71 ls3 engine but I don't under stand why they would put high performance heads on the lower compression engine it seems like over kill.
  4. 2ndGenCrazy

    2ndGenCrazy Veteran Member

    Aug 18, 2011
    Upstate New York

    Two completely different heads. They wanted to bump compression is my best guess.
  5. 2ndGenCrazy

    2ndGenCrazy Veteran Member

    Aug 18, 2011
    Upstate New York
    See post # 10 in the link that I attached to my previous post.
  6. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    My book shows that 3993820 is the correct head for a '71 LS3.
    Last edited: Aug 6, 2017
  7. Bikefixr

    Bikefixr Veteran Member Lifetime Gold Member

    Mar 13, 2006
    EVERY legit LS3 car I have seen and verified uses 820 heads.
    Send me pics of the car, tags, #'s. I'll add it into my registry of LS3 cars. Are you restoring or modifying?
    Last edited: Nov 1, 2018

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