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compression ratio on b20b 120-130

posted by  blueb20 on  Fri Sep 10 08:11 CST 2010
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last visit: Thu Mar 7 14:14 CST 2013
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hi guys,
i'm restoring a 70 model 122s b20b.
i'm planning to install ipd's isky vv71 cam c/w the hi revving kit, double wound valve springs.
the block will be rebored 20 thou oversize & the head will be gasflowed. the su carbs will be replaced with vpd's mikuni carbs.
now, the std cr on the b20b was 9.5:1.
is it advisable to go higher say to 10:1 by machining the head & block?

thanks chaps








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    compression ratio on b20b 120-130

    uid 43384's pic
    posted by  J.J. on  Sun Sep 12 14:05 CST 2010
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    last visit: Fri Sep 26 00:41 CST 2014
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    Do you have the mikuni's from JP yet? If not, then get yourself ready for a long wait.

    10:1 with a ARP head stud kit should work great!
    With all that head work, you might as well put in some hardened valve seats to enable running on un-leaded fuel.

    BTW, I'm also from SA.








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    compression ratio on b20b 120-130

    uid 37336's pic
    posted by  B20Paul. on  Fri Sep 10 09:19 CST 2010
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    last visit: Mon Oct 20 10:54 CST 2014
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    Tell us more about what will be done to the head.

    I would not spend a cent on Mikuni's until you have the best cylinder head possible & even then I would bypass them & go for Twin 45 or 48mm DCOE or DHLA or FOUR x 42mm Mikuni's on a custom made manifold, 2nd choice would be MegaSquirt. All the twin SU manifolds are dogs & bolting on new Mikuni's doesn't change that fact.

    If you haven't got the cam yet, then order a DUAL PROFILE.

    --
    Three 164's, Two 144's, One 142 & a partridge in a pear tree.








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      compression ratio on b20b 120-130

      posted by  blueb20 on  Fri Sep 10 09:38 CST 2010
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      last visit: Thu Mar 7 14:14 CST 2013
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      the passages in the head will be polished and in south africa we call it gasflowing.
      like i said, double wound valve springs, bronze guides, std valves.
      the mikinis will be bolted to a stand alone intake manifold & i had an exhaust branch custom made.








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        compression ratio on b20b 120-130

        uid 37336's pic
        posted by  B20Paul. on  Tue Sep 21 09:31 CST 2010
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        last visit: Mon Oct 20 10:54 CST 2014
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        the passages in the head will be polished and in south africa we call it gasflowing.

        I hope you mean port with a flow bench, you don't want to polish the inlet ports & you don't want to remove much metal on these heads.

        --
        Three 164's, Two 144's, One 142 & a partridge in a pear tree.







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