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350 vs. 400 whats the difference?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by SoulStyles, Jan 9, 2003.

  1. SoulStyles

    SoulStyles Registered Member

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    All right, I bout a 1977 Jimmy and I presumed it had a 350 in it. I ran the VIN number against GM's vin codes and it says my Jimmy was equipped with a 400. How can I tell if my engine is a 400 or a 350? Im new to 4x4ing so I could use a little help.

    Thanks a lot.
     
  2. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    I usually check for holes drilled or weights on the harmonic balancer. There is also a freeze plug difference sometimes but to me it is easier to check the balancer
     
  3. BurbinOR

    BurbinOR 3/4 ton status

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    Also check the block, should have 509 cast in it down underneath in front of the starter in numbers about 1" high.

    If it is a 400, that's a late Xmas present in my book. /forums/images/graemlins/thumb.gif
     
  4. SoulStyles

    SoulStyles Registered Member

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    so if it has the 509 cast in the block it is a 400?
     
  5. reddog64

    reddog64 1/2 ton status

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    The difference?

    My 400 spit a rod through the #4 cylindar wall at 10,000 miles.... /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif
    My 350 hasnt.... /forums/images/graemlins/smile.gif
     
  6. bigmack

    bigmack 1/2 ton status

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    You can also get the casting numbers off the back of the block beside the distributor and go to mortec.com and identify which you have. Cross your fingers /forums/images/graemlins/cool.gif.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    As the link above says, go to www.mortec.com But go with the suffix code. A little hard to read, but less likely to have the same suffix code on two different CID engines, unlike the casting numbers which sometimes were quite generic regarding CID.
     
  8. Blazer1970

    Blazer1970 1/2 ton status

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    No 400 will use the same casting number as any other small block. The 400 block is a totally different animal.
     
  9. BorregoK5

    BorregoK5 1/2 ton status

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    Another less reliable way of identifying the two is by looking at the freeze plugs on the sides of the engine, I think the 350's were more common to have 2 plugs per side and the 400 had 3 freeze plugs per side. Thats not a full proof rule because there are a few exceptions but it can help narrow it down. If it is a 400, then bonus, you'll love the torque it puts out over a 350.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    The casting number reference was just a general statement...if nothing else uses a 400 casting number, fine, but at least with suffix code you will know if its original (or very close) to the vehicle it is in, replete with HP #'s and year of vehicle. I mean if you are going to look at numbers, why not get ones that tell you a bit more?
     
  11. SoulStyles

    SoulStyles Registered Member

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    where do i get the suffix number? Is it in the same location by the distributer?
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    No, its listed at the www.mortec.com site, but typically it's behind the alternator, on the flat pad just in front of the passenger side cylinder head. Kinda hard to get too to clean off, but it's not THAT tough usually.
     
  13. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    The 400 block doesn't have a water jacket between cylinders 3 and 5 - 4 and 6. They call it "siamesed cylinders." This is how they were able to acheive the bore size with the same size block. They will alway run hotter than other small blocks. I know this doesn't help you identify it but it is the most significant difference other than CID that I can think of. /forums/images/graemlins/crazy.gif
     
  14. TorkDSR

    TorkDSR 1/2 ton status

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    dont let them scare you off...my dodge 318 runs way hotter than my 400... no complaints here. the torque is nice, specially if if you're not geared for big treads
    Ryan
     
  15. chevyracing

    chevyracing 1/2 ton status

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    The 400 is a good engine. Like some previous posters said, it will have 3 freeze plugs down each side rather than two. It may have a "fake" freeze plug but it is obvious. A 400 is externally balanced rather than internally balanced so you should be able to look at the harmonic balancer and tell if it has counter weights on it. On a 350 the harmonic balancer is actually a dampner. There are some differneces in the heads, flywheel, balancer, and oil pump drive shaft. The heads have steam holes drilled in them to help aleve the overheating problem. Typical 350 heads can be modified with steam holes to work. The flywheel and balancer are set up for an externally balanced engine, and the oil pump shaft has a little machining for clearancing.

    John
     
  16. BigBurban350

    BigBurban350 1/2 ton status

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    The 400 has a bigger bore (4.125in) and a longer stroke (3.75in) then the 350. /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     

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