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400 SBC

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Mreetz, Jul 30, 2001.

  1. Mreetz

    Mreetz 1/2 ton status

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    Well, I'm ready to start work on my 400 rebuild. I've got a 400 from a '72 truck. Bought a steel crank for it and I'm ready to do the buildup. Any suggestions on how to proceed? Like most, I'm concerned with low end torque.

    Thanks!!

    1984 K-5
    4" lift
    35x12.5 MTs
    buildin a 400 for it, any info greatly appreciated
     
  2. blazbrnc

    blazbrnc 1/2 ton status

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    I'm assuming you are doing a full rebuild. Tear it completely down and take it to a respected machine shop (ask around). Have them measure the piston bores to determine what overbore you will need. 030" is pretty typical. Have them measure the crank journals too. This will determine if you need oversize main bearings. I am assuming you are using the stock rods and heads? If so bring those along also. Once you know what size pistons and bearings to buy, you can order a rebuild kit (I've had good luck with Summit). It will include pistons, gaskets, bearings, oil pump. I would buy an aluminum intake also. With the intake you can get an edelbrock cam and lifters to match. The catalog will show what grind to get for torque. Have the machine shop hot tank and magnaglow the block and heads for cracks, overbore the cylinders, dust the cylinder deck face for flatness, clean up the crank if needed, press in the cam bearings, hang the pistons on the rods, and if you want it to last I would recommend balancing the pistons and crank. The heads will probably need to be faced and have new guides and seals. The machine shop bill alone will be around $800 at least. Oh yeah, the 400 is externally balanced. You will need to bring the flexplate and harmonic balancer to the machine shop and have them balanced with the crank.

    '79 K5, '79 Suburban, '76 Br**co, 77 K20
    '99 BB 4x4 Suburban to tow more junk home
     
  3. 88streetblaze

    88streetblaze 1/2 ton status

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    make sure you magnaflux or use another test to check for cracks especially in the heads
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    They did not put a 400 cid small block in '72 trucks from the factory. I guess you mean that you got a motor that had been swapped into a '72 truck?

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  5. Mreetz

    Mreetz 1/2 ton status

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    You are correct sir!

    1984 K-5
    4" lift
    35x12.5 MTs
    buildin a 400 for it, any info greatly appreciated
     
  6. Triaged

    Triaged 1/2 ton status

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    One thing you might want to look into is using 5.7" rods from a 350. They will put less side loading on the cylinder walls making more power and less ware.

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
     
  7. Rockjunkies

    Rockjunkies 1/2 ton status

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    Do not bore it anymore than necessary, make sure to use the right head gasket, and get your self a top of the line cooling system.

    Keep it simple!
     
  8. 88streetblaze

    88streetblaze 1/2 ton status

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    and if you want some added protection do what the circle track guys do, plumb a line from your water pump to the middle of your heads into the water jackets so they get cooler water to help stay cool and keep from cracking.. the siamise cylinders isn't the best design for longevity but in theory the hotter you can run it with out tearing it up it more efficient it is, but that is hard to practice....
     
  9. Mreetz

    Mreetz 1/2 ton status

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    These are all great ideas, I'll make sure and pass it on to the machine shop I end up going with. The one I think I'm going to have do it, is letting me do it on account..........

    on account I ain't got no money!!

    1984 K-5
    4" lift
    35x12.5 MTs
    buildin a 400 for it, any info greatly appreciated
     
  10. Andreas

    Andreas 1/2 ton status

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    Well, here´s what I´m doing with my 400.

    Got a two bolt 400 block bored .030. Two bolts are better and less prone to crack when it comes to sbc400. Honed for chromerings (finer stones I believe). Got Sterling Hypereutic pistons designed for 5.7" rods (Summit part#STL-H615P30). Used stock GM 5.7 rods with press fit. The Sterling pistons accept both press fit and fullfloating. I bought a set of Pink Rods. Fullfloating, but not bushed and the guy who does the machinework for me didn´t wanna use em´, so I sold them for more money than I bought them for[​IMG]. My cam of choice is a Comp Xtreme Energy 274 (230/236 .487/.490). Got new cambearings. Dynagear true rollerchain. Some machining had to be done with the rodbolts in order to not hit the cam. Rodbolts are ARP wavelocks btw. Stock nodular crank was already turned .010/.010 and got by with a polish. Bought a new flexplate. Balanced the whole thing (pricey!). Heads are 64cc ported 2.02&1.6 valve Powerpacks (old 283/327 medium heavy casting) with drilled steamholes. Got the later model with accessory bolt holes. The heads are resurfaced, new guides, screw-in studs and has polished combustionchambers. Bought Crane rollertip rockerarms. New waterpump. Intake is a Performer RPM with a Holley 750 sitting on top. 1&5/8" primaries and 3" collector Hedman headers. Stock mechanical fuelpump. 14"x"4 K&N filter and well......I´ll be breaking it in pretty soon. Hopefully within the next week or two. Keep your fingers crossed[​IMG]. This engine was built with 2000-5000rpm powerband in mind. Not all torque although Desktop Dyno gives me pretty flat 420+ ft.lbs torquecurve from 2000-5500, maxing out with 456 ft.lbs at 4500rpms. It should be enough[​IMG] At 5500rpms it´ll be spinning out 415 hp [​IMG]. I wonder how much fuel this one wants?[​IMG]

    Andreas

    406cui of pure sh*t[​IMG]
     
  11. RedDwarf

    RedDwarf 1/2 ton status

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    Triaged is right. The 5.56" rods from the 400 are not good power makers because of piston geometry.

    Longer rods also decrease chance of pinging.

    Lift It, Lock It, LIVE IT!!!
     
  12. Andreas

    Andreas 1/2 ton status

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    Well, the shorter rod is actually better for torque. The longer 5.7" rod is nicer to the engine and is beefier (more metal on the bottom end)

    Andreas

    406cui of pure sh*t[​IMG]
     
  13. Mreetz

    Mreetz 1/2 ton status

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    You all have been a great help. I really appreciate all the advice.

    1984 K-5
    4" lift
    35x12.5 MTs
    buildin a 400 for it, any info greatly appreciated
     
  14. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    I think it's magnaflux not magnaflow, or is it the same thing?

    If you didn't build it yourself, how can you call it yours.......?
     

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