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  1. #1
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    Default Building a BBC for boost.. Help

    Hey fellas,

    So lemme start by explaining what I have and what happened.

    The engine is a Gmpp zz502 BBC that started life as a bad oil burner thanks to uneven cylinder walls. Fixed that and it was pretty good but you know how bad the bug bites so I went with better carbs,solid roller cam from lunati, headers to get some more power but it didn't end there.

    Found a good price on a brand new 12-71 roots blower and couldn't resist it being a perfect fit on the engine so grabbed that and went with 8 psi and well this is where I couldn't find help with and blew a piston due to a broken valve.. I'm guessing my fuel pump is the culprit as it drops from 6 psi all the way down to 0 if I WOT.. regulator getting readings from carbs and from the spacer under the blower for when boost kicks in but I guess the fuel pump wasn't ready for that (140 GPH Holley black fuel pump)

    So now after feeling the roots blower I wanna build it the right way, I want this thing to live for ever. The instant power is mind boggling.. no I don't wanna try a different type of supercharger or go efi/ turbo..

    The looks, the power is just so good.

    So now the engine is out and apart and what I have is a good pair of 750 modded Holley carbs, the whole setup in cams/heads.. I have a set of long connecting rods and keyed crank from callies but dunno if I should build it bigger (540) before I actually need to (if I blow a rod/crank)

    will need a new set of valves/ pistons/ fuel pump is what I'm thinking but dunno how to go about getting the engine built for boost so that it can give me reliability.

    I wanna drive this thing whenever and for however long I need to. Daily driver reliability if possible.

    Please do give your opinions on how I should go about building it for the blower and enjoying it for years to come.

    Thanks in advance

    Sent from my Pixel 2 XL using Tapatalk

  2. #2
    427
    427 is offline
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    Default

    That is a big blower mate. As anyone will tell you, good fuel quality/supply and spark, not to mention a good quality forged bottom end are vital to making things live. Shame about the cylinder walls. Tough lesson..personally i am not a fan of crate engines. It is hard enough to get decent, honest workmanship when an engine is apatt..let alone when it is screwed together behind closed doors and you don't see a thing....

  3. #3
    Part of the furniture Deuce.'s Avatar
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    Default

    Forged bottom end, a drop in compression.
    Tune it fat, as lean will kill it fast. Keep it cool, blowers make heat.
    Sounds awesome. 12-71 is a good size blower.
    Keep info coming as it progresses

  4. #4
    Do you ever leave? EH179's Avatar
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    Default

    The Holley Black is probably responsible for the carnage... not adequate for a blown big block.

    Research Magnafuel or Aeromotive pumps, especially since we are talking two carbs now.

    Who is tuning the engine?

  5. #5
    427
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    Mate, hope you can get it hopping. I am thinking you will have to drop compression to around 9 to 1, probably more. Fuel supply will be paramount.
    Just thinking..is the bottom end of your engine forged?

  6. #6
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    mate I'm in on this one... and I agree with what is posted in the above comments

  7. #7
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    What a monster. Get your rings gaps spot on too. If regular driving, lose some power so you can tighten the gaps up. A bit.

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