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How to set up vintage Hemis for superchargers?

Discussion in 'The Hokey Ass Message Board' started by Hetzer, Feb 4, 2014.

  1. Hetzer
    Joined: Jul 28, 2013
    Posts: 8

    from Nebraska

    I have two vintage Hemis, a 331 and a 354. How would a guy set them up so they can run normally aspirated, and eventually put superchargers on them? What kind of pistons, etc. so the internals and other parts don't have to be changed again just so they can handle a blower?
  2. 73RR
    Joined: Jan 29, 2007
    Posts: 6,264


    The single biggest component that differentiates NA from pressurized is the pistons/compression.

    What engines, specifically? Pass car? Industrial? truck?
    What are the final plans? Streetable or race?

    The pass car, 51-54 331 had about 7½:1 c/r and could handle a few pounds of boost before the cast pistons fall apart.
    The 55 331 was labeled as 8½:1 and the 354 at 9:1...they won't like more than a couple of pounds on top.

    If you are installing a quality forged piston then you might start with 8:1. It will run ok with a carb but it still be 8:1. A good blower piston will handle more boost than you will likely want to use if this is a street car.

    You will also be faced with the camshaft dilemma. With faint compression you cannot get aggressive on the cam or it will be a dog. A mild cam with a blower is better than a wild cam and low c/r.

    You have now opened a can-o-worms and you will be besieged with opinions. BTW, how deep are your pockets?

  3. aaggie
    Joined: Nov 21, 2009
    Posts: 2,529


    There are more things to worry about besides pistons CR. The bottom end needs to be very stout as in line boring, precision balance job and very strong rods. You will be tempted to say that you will never get on it since it's just for looks but eventually you will put your foot in it and the carnage will not be pretty.
  4. Dynaflash_8
    Joined: Sep 24, 2008
    Posts: 3,012

    from Auburn WA

    I'd start by lighting my wallet on fire. Superchargers are kinda like that, then add the cost of a hemi in the mix, and bye bye bank account

    Sent via my typewriter
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  5. 296ardun
    Joined: Feb 11, 2009
    Posts: 4,154


    Think carefully before you start with a normally aspirated engine and then try to add a blower. A long time ago, if I built a blown engine, I started from scratch planning the extra boost and stress. Strong bottom end, as noted above, blower pistons, extra bearing clearance, and o-ringed both the block and the heads. Granted I was building a competiton engine, but even a blown street engine needs to be built from the start as a blower engine. Just my thoughts, others might disagree, but all of us want to see you have fun with your hemi without regretting a later choice of a blower.
  6. Bent Wrench
    Joined: Jun 18, 2009
    Posts: 19

    Bent Wrench

    A blower motor without a blower is a dog.

    AN NA motor with a blower is a time bomb.

    If you want a blown motor build it and put the blower on it. It's not something you can sneak up on. Your entire engine compartment will be different why buy all those parts twice? Don't forget the radiator, trans, and rear gears won't be the same either for a blown application.

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