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Thread: BBC builders

  1. #1
    Junior Member APPRENTICE
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    BBC builders

    I am looking for educated advice from BBC builders. This is on a 427 BBC. I rebuilt this engine earlier this year with the hopes of making big gaines in ET and have seen no improvement. The only things that were changed in the rebuild was the bore increased .010 to 4.320 and new CP 47cc domed pistons installed. The engine was 9.3-1 prior to the rebuild and is now 12.2-1. That is almost a 3 point increase in compression with no change in ET. Is my combination way off or could it be that my domes are severely limiting flame travel?

    454 block bored to 4.320
    3.76 stroke
    6.135 H beam floating pins
    CP custom 427 47cc pistons
    assembly balanced
    Solid roller cam, lifters and rockers, stud girdle
    677/712 lift
    252/262 duration @ 50
    108 lobe center
    102 installed centerline
    stock Merlin Iron 320cc runner, 119 chamber rectangle heads with 2.3/1.88 valves
    stock Team G 2" plenum intake
    Pro-Systems 1000HP carb
    Hooker 2" OD 1 7/8 ID headers w/ 18 extensions

    Thanks in advance.

  2. #2
    Senior Member SENIOR BUILDER chevynovaman's Avatar
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    Was there any difference in the weight of the pistons? you should have gained some low end power with the higher compression... good luck..
    1968 CAMARO 302 4 SPD IN THE ROUGH
    1957 CHEVY FUEL INJECTED LS1 4L60E BEAUTY
    1962 CHEVY II NOVA 496 LETS RACE

  3. #3
    Senior Member RACING JUNKIE
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    hey travis, i like your specs on your motor, since you moved up
    on your compression i think your cam will work well, the only thing
    i can think of is the strok or the breathing, your cc went from 119 to
    36 after the 47cc domes, you might benefit better with 350 runners
    with that size of valves 2.3, thats big, and i have seen better results
    with the vic jr intake for better breathing, and with that comp. are
    you running a vacum pump? and i guess all your running now is
    racing fuel, also you did not mention ignition or what distrib you
    are using, good luck bud :wink:

  4. #4
    Senior Member RACING JUNKIE
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    good advice from signs on the intake,

  5. #5
    Senior Member RACING JUNKIE
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    X2 on ditching Team G, it's definelty holding you back.

    I run a dart single plane on my BBC 496 with good results but a Vic jr is a good choice too.

    Did you change the jetting on the carb?

    More compression should warrant more fuel, I'd go up at least 2 jet sizes for starters.
    What is your total timing?
    Mine likes 40 with 110/112 leaded race gas any lower than that and it's a pig.
    Your heads sound plenty big, your cam could be holding you back some too.
    Another thing is your convertor could be too loose fro your new combo, just food for thought.

    Goodluck, Cp
    ***IN GOD WE TRUST***

  6. #6
    Senior Member SENIOR BUILDER
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    x 3 on ditching team G,

    x 2 on heads plenty big,

    what fuel are you using, before and now...

    need lots more info on car, trans, convertor, gears, tire, weight, et, mph.. :?:

  7. #7
    Junior Member APPRENTICE
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    additional information

    Additional specs. The car is a 69 Camaro weighing in at 2950 wet.

    msd pro billet distributor
    38 degrees locked out timing
    digital 6 plus ignition
    running vp 110 same that I was running when it was a 9-1 motor
    4 link backhalved with 29.5 x10.5 tires no problems launching
    powerglide w/brake
    8" 4500 converter
    9" with 4.56 gear
    shifting at 6700
    trapping at 7000

    ET 10.10 at 133 with the 800 holley I had on it before I installed the pro systems carb, I did play with jetting and timing for the past 4 months trying to improve my times before the carb swap. The carb change has gained 2/10's but I was expecting to see this motor run 9.80's after the engine build. I suspect the problem is somewhere in my engine combo but I am not sure what to change at this point.

  8. #8
    Junior Member APPRENTICE
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    I did install an evac kit running to the headers to help with the pressure in the engine as well.

  9. #9
    Senior Member SENIOR BUILDER
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    how does the car 60'? before and after the carb change?

    the carb change helped 2 tenths, what about mph?

    what altitude you running at? DA?

    what gearset in the powerglide? 1.76?

  10. #10
    Senior Member RACING JUNKIE
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    Back to the carb swap, you say you played with the 800 then swapped to the 1000cfm when you rebuilt the motor, have you done any tuning on this carb since the rebuild?

    If not I'd jet it up till the mph slows and give the motor some more timing, 40 to 41 TT.
    JMO>Cp
    ***IN GOD WE TRUST***


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