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383 or 350?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by clubba68, May 2, 2003.

  1. clubba68

    clubba68 1/2 ton status

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    The truck I am looking at has been stroked 383 according to its owner. It was apparently done before he owned it so not sure of shop that did it. Is there any way of telling by looking at markings, anything whether it is actually 383 or he is just blowin' smoke?
    Thanks,
    Andrew
     
  2. MJF

    MJF 1/2 ton status

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    I'm no expert but I think you have to pull it apart to find out. If my thinking is right, a 383 is a 350 block with a 400 crank, rods, & ????(not sure what else).
     
  3. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Yep, a 383 would be a bored and stroked 350.
    You'd be able to tell by measuring the bore and stroke, which is easiest to determine when the engine is apart.

    350 = 4.000" x 3.48"
    400 = 4.125" x 3.75"

    383 = 4.030" x 3.76" (5.565" or 5.7" or 6.0" rod)
    350 block bored .030" over and a 400 crank, main bearing crank journals turned down to 350 size.

    The thing that really determines it is the stroke of the engine... You could pull a head off and measure the cylinder to find it is .030" over, but that won't tell you if its a 030 over 350, or if it has a stroker crank making it a 383.

    I don't know of any easy way to identify what you have since it's the internals that determine it.
     
  4. Beast388

    Beast388 1/2 ton status

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    One option you may have is to look for the externally balanced harmonic dampner and flywheel. Most, but not all 383's will have these because most stroker cranks are externally balanced.

    It isn't a sure way to tell, but if you run the block numbers and it says 350, but it has the ex. balanced dampner & flywheel, most likely it is a 383. /forums/images/graemlins/thumb.gif
     
  5. Chris_T

    Chris_T 1/2 ton status

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    Look for the balancer - that would be my suggestion as well. The only other way I can think to do it is to get a cylinder at bottom dead center, fill it with oil, let it settle and then push it to top dead cylinder and measure what comes out.

    350 cu in / 8 = 43.75 cu in .7125 L
    383 cu in / 8 = 47.875 cu in .780 L

    if my math isn't wrong ... think you can measure the difference? Nahh .. just look for the balancer
    Even
     
  6. Don

    Don 1/2 ton status

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    If for some reason You happen to have a head off, simply roll the engine over, bring a piston down to the bottom of it's stroke, and measure with a tape, or vernier caliper, if it's close to 3 3/4" it's a 383. if it's close to 3 1/2" it's a 350. /forums/images/graemlins/shocked.gif
     
  7. kiley

    kiley Registered Member

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    If my 350 is already bored .030" over do I just need the crank and connecting rods to go to a 383?

    What is the displacement of a 350 thats bored .030" over but not stroked?
     
  8. Chris_T

    Chris_T 1/2 ton status

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    Parts wise yes, but to give the rotating mass more clearance you'll need to have some machine work done to the block. You'll also need to externally balance the engine as mentioned above.

    A 350 bored .030 over is a 355
     
  9. kiley

    kiley Registered Member

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    I've read about scat cranks for a 350 block and it seems like they are just a "bold on" project. Know anything about these cranks?
     
  10. Beast388

    Beast388 1/2 ton status

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    I have a Scat stroker crank in my 388. They are a bolt in, but you will need to clearance the oil pan rail as well as a few other areas to clear the counterweights on the crank as well as the rods. I did all of the clearancing myself, with a flex-shaft equipped Dremel. It took some time, grinding, test fitting, grinding some more etc. /forums/images/graemlins/thumb.gif

    If you have ever compared the bottoms of a 350 and 400 block, you will see the factory cast-in clearance on the 400. /forums/images/graemlins/thumb.gif
     
  11. kiley

    kiley Registered Member

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    If I get a crank that needs to be externally balanced does anything else need to be changed other that machining the block like does the distance between the engine block and the torque converter/transmission change?
     
  12. Beast388

    Beast388 1/2 ton status

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    Not at all, that distance will not change. Externally balanced engines use a weight on the flywheel and harmonic dampner to balance the rotating assembly. /forums/images/graemlins/thumb.gif
     
  13. Roostr84

    Roostr84 1/2 ton status

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    I dont know if you assumed this or not but I figured I would put it out there too. Pistons.....everyone is talking about just changing crank and rods. You have to have the correct piston height too.
     
  14. Beast388

    Beast388 1/2 ton status

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    Yep, you are correct Chris. Rods don't need to be changed, but crank and pistons do. /forums/images/graemlins/thumb.gif
     
  15. Triaged

    Triaged 1/2 ton status

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    Or you can get 400 rods and just use some regular 350 pistons.

    Not what I would do but still another option.
     
  16. Roostr84

    Roostr84 1/2 ton status

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    Triaged, I'd like to know more about using the stock 350 piston. By my calculations the 400 rod is 5.565 in length vs. the 350's 5.7 inch rod a difference of .135. We know the stroke is 3.75 vs. 3.48 a difference of .27. My question is this how would the extra .135 affect the compression and clearence to the valves and deck etc utilizing the stock pistons. I guess it would be more of a factor in higher compression engines than lower. Thanks
     
  17. kiley

    kiley Registered Member

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    I don't know much about this so I'm still learning. I figured that since my engine had already been bored and had new pistons to fit that bore that all I needed to do is get the crank and connecting rods.
     
  18. Roostr84

    Roostr84 1/2 ton status

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    well my thought was how would it affect the piston height, thats all. I would hate to assemble an engine only to find that the piston sits to high in the cylinder or worse makes contact with other parts.
     
  19. Beast388

    Beast388 1/2 ton status

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    Chevy 400 pistons and 350 pistons have the same compression height of 1.561". The increased stroke of the 400 is compensated for by making the 400 rod one half the difference in stroke (3.75-3.48=0.27/2=0.135) less than the 350's rod(5.7-5.565=0.135). I hope that made sense. /forums/images/graemlins/thumb.gif

    It is really disadvantageous to use a shorter rod, the increase in friction, and less piston dwell time all hurt the longetivity and power making potential of an engine. When I built my 388, I really considered going with a 6" rod instead of the 5.7s. The only reason I didn't was that with a rod that long, the wristpin in up into the oil rings. I didn't want to mess with oil ring failure or using the support plugs on the end of the wristpins. The compresstion height goes from 1.433" to 1.133".

    I hope this helps..... /forums/images/graemlins/thumb.gif
     
  20. Stroked72Blazer

    Stroked72Blazer 1/2 ton status

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    [ QUOTE ]

    It is really disadvantageous to use a shorter rod, the increase in friction, and less piston dwell time

    [/ QUOTE ]

    I agree, and further more you end up with the rod at a more extreme angle after BDC before the piston starts to move up. This can cause the piston to get pushed through the side of the block in extreme aplications and RPM's. And an extreme RPM for a shorter rod is much lower than with the longer rods.

    Now heres the downside. You need more $$$$$$$$$ with longer rods because you have to use custom pistons with a custom pin hight.
     

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