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Thread: 540 bbc low vacum

  1. #1
    Junior Member APPRENTICE
    Join Date
    Jul 2007

    540 bbc low vacum

    To all that can help, i recently put to gether a 540 using dart block lunati pro rotating assembly 4.500 bore x4.250 strokex 6.385 rod. Piston is in the hole .010. heads are brodix bb-2 plus that have been ported and flowed AT .700 LIFT INTAKE WAS 377 EXH. AT700 WAS 296THE HEADS WERE MILLED DOWN TO 112CC the gasket is felpro .041 thick and the flat top piston has a valve releif and is 4cc . The compresion should be9.6:1. Cam is a solid roller isky .313 dur. and @.050 276 / .730 lift and cam is degreed in at 106.375 of a degree. and intake is brodix hv2000 4150 flange with a quickfuel 950 mech secondry pro series carb. the carb is out of the box with 80 jets in the primary /86 secondary . DIST . is msd billet mech. using the blue bushing and blue springs. timing / initiel is at 14 degrees {isky recomends 12 to14 } toltal is 35 degrees and is in at 3000rpm . Ialso and using a star machine vac pump that has been set up at star machine for my application The problem i have is at idle at 1000rpm in park i only have 4" of vacum and in gear 1"to 0" of vacum . Driving the engine is very reponsive but when stopped the engine needs to be lightly thottled.

  2. #2
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
    Join Date
    Mar 2008
    Emmett, Idaho

    Lots of cam = loss of vacume
    to those who

    God Bless our folks in uniform
    "We the People, have your backs"

  3. #3
    Senior Member RACING JUNKIE oldandtired's Avatar
    Join Date
    Dec 2008
    Sugar Hill, GA
    In my opinion, you have a bad mix of parts. That big of a cam with only 9.6 static compression ratio probably gives you a dynamic compession ratio of about 6 to 1. An engine is nothing but an air pump and the cam is bleeding you to death.
    You might try advancing the cam to close the intake valve sooner.
    Good luck.
    "All that is necessary for the triumph of evil is for good men to do nothing" Edmund Burke

  4. #4
    Senior Member RACING JUNKIE
    Join Date
    May 2003
    Coldwater, MI
    I didnt know star could set them up for you without being on the motor ? You will need to adjust the pressure regulator on it so it pulls more vacuum. If not you have a vacuum leak somewhere .. which may explain the bad idle

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