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  1. #1
    Jimmy C
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    Default Intake/Exhaust Valve Size?

    I have an '81 Corvette, all original. I am planning an engine build and want to know if anyone has torn down one of these L-81s and checked (f/sure) what size valves are in the heads of the L-81 engine. I looked up the casting number on Mortec, and it only shows '75-'86 350/400 76cc 1.72", 1.94" or 2.02" intake. I've been told by afew that the heads on the L-81 have the 2.02"/1.60" valves, but as detuned as that year is, I have my doubts.
    Thanks in advance f/ any (f/sure) info on these heads.

  2. #2
    Member 73shark's Avatar
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    What's the casting number? Does it have the double peak casting marks?
    Save the wave

  3. #3
    Technical Writer for Internet & Print Media
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    Your information is correct. An L81 may have either 1.94 or 2.02 in intake valves. The casting number should be 462624. You'll probably need to get the head off an measure the intake valve size to know which on you got, but if they're 1.94s any decent automotive machine shop will be able to install 2.02s.

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    One of the worst heads every put on and engine. Best thing you can do is change them

    Groeten Peter

  5. #5
    Jimmy C
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    Shark, The casting number is 462624, as Hal said. (Good seeing you here, Shark.)
    Hal, Are you saying that the '81 L-81 could have 1.94" or 2.02" intakes in it? This engine came w/ either/or due to...what?
    Peer, Why do you say that these particular heads are so bad? Is there some specific problem w/ this casting number?

    Thanks in advance.

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    Member 73shark's Avatar
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    Glad you could make it, Texas.

    According to my old parts book (Rev 3-83), the '81 & '82 used the same intake valve, P/N 14025572. Unfortunately it doesn't list size. That was the only years that P/N was used, so probably not 2.02"

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    These heads crack very quickly is what I read everywhere. Do a search on google with the number. On the other hand, if you keep them you know where the weak spot is in your engine

    Groeten Peter

  8. #8
    Jimmy C
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    Fellas',
    Found out that the 1981 L-81, the LM-1(ZDD) is a (14010207) 4-bolt main and the heads (462624) have 1.94" intakes and 1.50" exhaust valves.
    In any case, Peer, the valve size makes the head an unwanted item f/ a performance build-up.
    Thanks to you guys who took the time and effort to reply.

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    Is that the original L81 short block? I thought the L81 always was a 2 bolt main... Non the less, a 4 bolt is better then a 2 bolt
    Good luck!

    Groeten Peter

  10. #10
    Jimmy C
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    Quote Originally Posted by Peer81 View Post
    Is that the original L81 short block? I thought the L81 always was a 2 bolt main... Non the less, a 4 bolt is better then a 2 bolt
    Good luck!

    Groeten Peter
    Hey Peter,
    Yes, it's the original. The block casting number shows that it comes either 2 or 4 bolt, and further research shows that the L-81 (LM-1 ZDD) is a 4 bolt. The LM-1 started back in '68-'69 and took the place of the L-30 in some vehicles ie; the Camaro. The LM-1 350 came w/ heads that had/have bigger combustion chambers (76cc) rather than the L-30s heads w/ 62cc chambers. The LM-1 made less HP but (f/ some reason) more torque. I thought that it's interesting that the LM-1 goes back that far and still uses a 76cc chamber head, not that the head is of any use to me.
    Thanks again f/ your time and effort.

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