i found a stock chevy 400 small block. should i buy?

Discussion in 'Engine Topic' started by matthamilton, Jan 8, 2013.

  1. matthamilton

    matthamilton Member

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    so I have been looking for a better engine to replace my 350. especially since the last guys who built it never gave me the specs...:mad: :mad:
    But anyways I have found a Chevy small block (stock) and I want to rebuild it on my own. Now I want to know if this is a good investment. I want more horses. Now has anyone worked on one of these or rebuild one for performance?

    The motor is all stock and I want to make it a 406.
    Pistons I was thinking of summit.
    now I am not sure about a good cam.
    and can I use the heads? or should I order aluminum heads?
    also for an intake I again was looking through summit but im not sure what is best for fuel delivery.
    And this will be my first motor rebuild!!
    any extra tips are welcomed.
    :) :)
     
  2. mjoc

    mjoc Veteran Member

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    Get forged pistons and rods, get good aluminum heads and go with a compression ratio around 9.5 to 1 it wont give you huge power but a lot more then the 350. but it leaves you the option of putting forced induction on it later and really making A LOT of power.. With the 9.5 to 1 you can use 87 octane too.

    Michael
     
  3. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

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    A few things to note on a small block 400.

    It will have shorter rods than other small blocks. (400's have 5.565" rods while all other small blocks have 5.70" rods)

    It will require any replacement heads to have steam holes drilled. (Not a difficult task)

    It can provide much more lower end torque and will handle a larger cam for street use.

    It requires an externally balanced flexplate/flywheel and harmonic balancer.

    To build an ideal street engine, I would recommend you get a complete crank kit with new 5.7" rods and make sure to get it balanced with a new flexplate / flywheen and balancer.

    Newer cylinder heads including Vortec's will offer vast improvement in breathing efficiency and performance. Aluminum castings are reasonably priced and can help with building the engine with higher compression compared to cast iron heads for street use.

    Camshaft will depend on the rest of the drivetrain and your intended usage. Automatic transmissions might require a stall convertor and additional fluid cooling if you get into a high duration cam. You might also have to consider power brake vacuum canister if you get so radical that you don't produce sufficient vacuum to assist your brakes.

    Rear axle ratio and rear tire diameter will also affect or be affected by your cam selection.

    The highest consideration is what type of driving you are intending on doing with the car. If it is spending more time on the street, build it for low end torque and don't get carried away with radical sounding cam profiles that will be a headache to drive and a pain in the wallet to feed.

    Let us know what you budget is and more information about your car, and then we can help guide you with suggestions.

    Good luck!
     
  4. Smokes

    Smokes Veteran Member

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    1st. How much are they asking? Don't shell out too much even though its a 400, a good rebuildable 400 is useally worth around 300.00 give or take say 50.00 bucks, thats carb too pan.

    You can rebuild the engine stock if funds are down, even the stock heads will do IF there in decent shape & don't need a ton of work, with a mild cam & bolt-ons you'll a torque monster, I got caught up in all the "you need higher compression & better heads", Only if your wanting around 375-400+ HP you don't really need this stuff. You can run the stock bottom end & either the smogger heads or even a set of Vortecs. I had a bone stock 400 in a 78 2wd. Blazer back when & it hauled azz, had tons of torque.
     
    Last edited: Jan 9, 2013
  5. rustbucket79

    rustbucket79 Veteran Member

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    Word of caution on the 400's, they've been out of production for a long time now, if you can, negotiate the purchase contingent on it being a crack free, rebuildable core. (IE one that will bore to .030" over)

    If you're trying to build this on a limited budget, you can do so provided you buy the correct parts. For a 375 HP engine, the stock crank and rods are more than up to the task. If your replacement pistons are within 25 grams of the originals, you don't need to balance.

    2 main trouble spots on the 400's, the decks need to be milled 99% of the time, and the cyliinders MUST be honed with torque plates installed.
     
  6. Louich

    Louich Veteran Member

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    I put one together a while back, stock crank and rods, hyper flat top pistons, 292 comp cam and set of trick flow older twisted wedge heads, thing ran 12.2 all day long on pump gas. And drove great on the street.
     
  7. HyPer

    HyPer Veteran Member Lifetime Gold Member

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    I've a vintage Dema Elgin cam for your build, if you want.

    hydraulic flat tappet
    adv dur: 298/301
    1.5:1 lift: .499/502
    6 degrees advance cut

    It's been sitting in it's transport tube collecting dust for a few decades now.
     
  8. scot1074

    scot1074 Veteran Member

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    I second the torque plates, make sure the machine shop you work with even has them. I built a 406 with 5.7s. I lost all my compression cause it wasn't done with plates when I specificly asked for that to be done. Oh and if your going roller then a small base circle cam you will need
     
  9. DoubleR

    DoubleR New Member

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    You definitely want them to guarantee it to b crack free. I bought 3 blocks and only 1 was good. Otherwise great motors build lots of power. My old one had a small mechanical cam and everything else stock except intake and carb and was really fun on the street. I've got one now that has a lot n it but now wanting a LS. I may have some 400 parts laying around have to look next month when I get home. Fun street motors cost the same to build as a 350 but gain cubic inches
     
  10. trmnatr

    trmnatr Veteran Member

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    With GM 291 Camel Hump Heads, a solid flat tappet, 100 LL Aviation Fuel, and stock crank, stock rods, flat top pistons, will yield you up to 525 to 550 Horsepower. Sure when your talking over 475HP your talking a limited street use combo, kind of the combo you drive to and from work a few times a year, and cruise around or bracket race on the weekends when its not raining

    The combo we had which is very mild, and I will tell you everything which was done, ran 10.13 to 10.22 @131-133mph in a 1980 Camaro, race weight 2850 pounds. With a three speed TH350 or TH400 I feel it would have been about a tenth to two tenths faster. I will post the info later with the complete combo
     

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