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Big Block swap and whats needed ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by twenty_below0, Apr 10, 2003.

  1. twenty_below0

    twenty_below0 1/2 ton status

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    Considering the BBC instead of the monster 420 , so what will it take to do the swap ?
    Different TH 350 with big block bell housing ? All attachments for alternator etc. or do the
    brackets work that are on my small block now ? Also will the motor mounts work just
    move them back or forward ? So let me know and I dont have access to a junk yard with
    all the cheap parts I would need . So let me have it , the best way to do the conversion . /forums/images/graemlins/eek.gif
     
  2. zakk

    zakk 1/2 ton status

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    A complete BBC and headers, mix. done.
     
  3. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Just did the swap myself about 8 or 9 months ago. The motor will drop right in the truck like is was meant to be there. Tranny is the same, motor mounts are the same. The only thing ya need is big block accessory brackets, power steering, alternator ect. The small block ones are different and will not work. The best thing to do is get a donor truck with a big block in it. That way you'll have everything ya need. Thats what I did. Had the SB out and the BB in and running in 7 or 8 hours. /forums/images/graemlins/thumb.gif
     
  4. twenty_below0

    twenty_below0 1/2 ton status

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    So I wont need to move the motor mounts or change trannies ? The bell housing is the same on sm. block or big ?
    If so thats great , all I need is motor and brackets , right ? I'm really considering this . /forums/images/graemlins/eek.gif
     
  5. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Any GM trannsmission- TH400, TH350 700R4, SM465, SM420(I think) NV4500, Allison, ect ect, will bolt to any GM V-8 and the 4.3 V-6 if I remember correctly. I've had three different tranny's behind my big block...TH350, TH400, and SM465. /forums/images/graemlins/eek.gif /forums/images/graemlins/thumb.gif

    Your small block motor mounts will work just fine too. My big block is sitting on the same mounts that the small block was. Like you said, all ya need is the motor and brackets. I even used the same power steering pump and alternator. Good luck with the swap. /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif
     
  6. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Although the BBC will fit in the SBC mounts, the engine is much heavier. It would be a good idea to use new mounts or get the High Energy poly inserts. Changing them with the motor out is a 20 minute job, as opposed to a PITA and much longer time when the motor is in. Plus if you have ever seen a stock SBC motor mount break from a BBC, it is not a pretty site (I'VE SEEN IT). Just food for thought. As stated it will bolt up to tranny (assuming dual pattern flywheel.....check that FIRST before lowering engine into bay), Acessories and brackets will be needed for BBC, larger radiator MAY be needed (if it's a 3 core you might get by, if it's a two core replace it). I run a SBC400 with a 4 core radiator (it cost me $100 thanks to CK5's discount for the radiator, and about $40 bucks for the 4 core cushion), but plan to go BBC so I am already set. The exhaust will need to be changed somewhat (at least headers/manifolds), and tires will need to be changed (after you smoke them /forums/images/graemlins/rotfl.gif).
     
  7. twenty_below0

    twenty_below0 1/2 ton status

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    OW yeah ....I like the nick name leadfoot . I have a stout sbc now (380/410) but I want more
    and after you drive it for 10,000 miles it gets old . So I think the big block is ultimately the way to go
    I have seen some nice BBC on ebay for 3500.00 with accessories but I want to build one myself since all my
    experience is with sm. blocks . So which is the best way to go with big blocks buy after market heads at
    about 1800.00 or so a set , or can you get what you need from certain old closed chambered heads ?
    What would you suggest and keep the compression at around 9:7:1 . The big blocks dont seem to be really
    that much more to build than a sbc . Also can you run longer rods with a standard say 454 or does it need to be a tall deck ?
    All info is needed , as I said I have never dealt with BIG BLOCKS . /forums/images/graemlins/thumb.gif
     
  8. HarryH3

    HarryH3 1 ton status Author

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    If you want to know how to build a big block that will alter the rotation of the planet, PM Shawn. /forums/images/graemlins/cool.gif That 496 in his Blazer is un-freaking-believeable!!! /forums/images/graemlins/thumb.gif
     
  9. twenty_below0

    twenty_below0 1/2 ton status

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    So who is Shawn and how do I get him to help me out with the build plans ? "Alter the rotation of the planet" /forums/images/graemlins/eek.gif......thats what I want!!! /forums/images/graemlins/grin.gif
     
  10. MOABDADC22

    MOABDADC22 1/2 ton status

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    [ QUOTE ]
    So which is the best way to go with big blocks buy after market heads at
    about 1800.00 or so a set , or can you get what you need from certain old closed chambered heads ?


    [/ QUOTE ] Keep an eye out for a decent set of used 290/291/292 heads on e-bay.

    [ QUOTE ]
    What would you suggest and keep the compression at around 9:7:1 .

    [/ QUOTE ] Just like a small block, if you start getting too high of a compression ratio, the fuel/timing settings are pretty touchy.

    [ QUOTE ]
    Also can you run longer rods with a standard say 454 or does it need to be a tall deck ?

    [/ QUOTE ] If you go with longer rods, you will have to get pistons that are specific to that rod. (Different wrist pin location.) Tall deck blocks are actually very rare to find in a passenger car/truck. They were used primarily in BIG trucks.

    If you are on a budget, you can modify you SBC alternator and PS pump brackets to work on a BBC. If you do go with a BBC and buy the brackets for the alt/ps, make sure you get the correct brackets. BBC's came with either a "long" water pump or a "short" water pump. Only 3/8" difference btween a long/short, but the brackets are not the same.
     
  11. twenty_below0

    twenty_below0 1/2 ton status

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    OK could you give me a little more info on the 290-292 heads I need to look for if building a good BBC . Also the rods are subject to pistons as with a SBC (I assume the way you describe) So theoretically I could run a longer rod with a standard block.....correct . Without needing the tall deck . This is what I'm wondering . Couple more curious questions , how are the 409's I've heard they are screamers but people have trouble getting them to hold together....is this mith or some truth to it ? Also it seems to me that a big block with 400 horse and 450 ft. lbs is a much stronger motor than a small block with the same numbers.....why is this ? As you can see I have so many questions , so bare with me I dont mean to be pushy just was taught no question is a dumb question . (with in reason) THX for all the info ! /forums/images/graemlins/thumb.gif
     
  12. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    So who is Shawn and how do I get him to help me out with the build plans ? "

    [/ QUOTE ]
    Uh, send a PM to username "Shawn"? /forums/images/graemlins/wink.gif

    Here's a link to the buildup of his Blazer: http://www.off-road.com/chevy/rodent/
     
  13. MOABDADC22

    MOABDADC22 1/2 ton status

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    [ QUOTE ]
    OK could you give me a little more info on the 290-292 heads I need to look for if building a good BBC .

    [/ QUOTE ]

    3964290 ....69-70...oval port..CLOSED..101cc chamber LS-5 396/402/427/454
    3964291 ....69-70...rect port..CLOSED.. 2.06/1.72 375hp, 425hp & 435hp 108 CC Chambers 325cc Intake Ports
    L-78/L-71/L-72/LS-6 396/402/427/454

    6272292....70-78...oval port...OPEN...
    2.06/1.72 240 & 270hp LS-3/LS-5 402/454

    [ QUOTE ]
    Couple more curious questions , how are the 409's I've heard they are screamers but people have trouble getting them to hold together....is this mith or some truth to it ?

    [/ QUOTE ] from what I know ( I am no expert) this is just like anything else. Some people swear against them and others swear by them. I have never heard this before.

    [ QUOTE ]
    Also it seems to me that a big block with 400 horse and 450 ft. lbs is a much stronger motor than a small block with the same numbers.....

    [/ QUOTE ] I agree....but comparing a high revving 383 or 400 SBC to a smilar sized 396/402 BBC is like comparing apples to oranges. Both have benefits and both have faults.

    For my muscle cars, I simply prefer a BBC. Part of that is nostalgia, horsepower, and cosmetics ( you got to admit that a big block cars just way cool /forums/images/graemlins/thumb.gif.)

    Every truck/Blazer I have owned has been a small block for the simple reason that I do not really need lots of horsepower to rock crawl or to use the vehicle in the way that I do.
     
  14. b454rat

    b454rat 1/2 ton status Premium Member

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    Tranny bell is the same, and look for dual pattern flex plate it an auto. Convertor bolt holes are different. BBC will drop in on SBC mounts. The BBC ones are stiffer and stronger, but the SBC will work, have two vehicles with them and no probs here. The alt and p/s brackets are different, as the fuel and p/s pump itself. Somehow I hooked up SBC pump/bracket up to my car, but can't remember how to do it. If you are running headers, the exhaust will have to be shortened a little at the collector. As for rods, if you aren't stroking it, then I would keep the ones you have, 6.135" stock. BBC don't have the rod ratio prob like the 400 did. If you do want the longer rods, just get the pistons that match the rods. For heads, those 290-292 heads are good, but will be kinda hard to find. I have a set of 049 heads, believe they are for 73-82 trucks, and some cars. This is just what I have heard, but these are supposed to be kick ass, oval port heads, from the smog era. There is a guy in my town that built motors with these heads and run in the 9s with them, in a chevelle. Put the bigger valves in, open up the exhaust side a little, port/polish to clean up any ridges/burrs, and gasket match the intake side. Also, 781 are good ones too. If you call a reputable engine builder, he can tell you what heads are good. An engine builder told me that you can't put anything in a BBC to make it slow!! I have four 454s and I can vouch for that!!!!
     
  15. twenty_below0

    twenty_below0 1/2 ton status

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    OK , thx for the info Moab I'm well on my way to the beginning of the end of my SBC era and I think once I switch I will never go back . I will keep you posted on the first build and when it's done . /forums/images/graemlins/thumb.gif Oh wanna buy a nice small block ? /forums/images/graemlins/grin.gif
     
  16. MOABDADC22

    MOABDADC22 1/2 ton status

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    [ QUOTE ]
    Tranny bell is the same, and look for dual pattern flex plate it an auto.

    [/ QUOTE ] If you are building a 454, you will need a flexplate made for a 454. A 454 is externally balanced and takes a special flexplate and harmonic balancer. All other BBC's are the same though.
     

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