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383 vs. 400

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Roostr84, Dec 16, 2002.

  1. Roostr84

    Roostr84 1/2 ton status

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    Well I am building an engine for my 69 K5. I have to decide whether to build the 355 block I have now into a 383 or build the 400 I have here. I am basically looking for any opinions on the 400 that anybody has as far as reliability with the siamesed bores etc. I know you have to drill steam holes in the heads for the 400 but I figure you have to clearence the 350 for the crank anyway so there is machining involved in both. Anything else I am missing.
     
  2. Robin

    Robin 1/2 ton status

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    From what I've heard, 400's are getting quite rare whereas 350's are dime-a-dozen (though somehow I spent $3K making my 4 bolt 350 a 388). I'd recommend leaving the 400 in a state where it will be of some value to someone who is interested in restoring something.

    The 388(60 over) is pretty darn close in displacement and parts and machine work is quite common.
    Also one thing that caught me by susprise, early in the stroker exercise, was that you have an externally balanced crank now (over the 350). This means you need to get a 400 harmonic balancer and ring gear and balance the rotating assembly with all these pieces. The 350 can be balanced without the external parts. No big deal, it just adds up...
     
  3. Roostr84

    Roostr84 1/2 ton status

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    Thanks for the reply Robin although I have to say I don't really know how much a non numbers matching engine in a restoration would be worth esepecially since these came out of so many less sought after cars in the 70's save for a few chevelles. In any case I have built a 383 before actually so I know about the balancing etc. I actually had to have a custom welded flywheel built to work with with the combination I was running but in any case I understand what you are saying. Thanks again!
     
  4. ben427

    ben427 1/2 ton status

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    Go with the 400 if its a 2 bolt main, you wont be dissapointed, use 5.7 inch rods from a 350, it will give you more all around power than a 383 will. I have a stock 400 in my basement thats going through the process of a torqe rebuild for my truck, sould be good for 350 HP and 450 lb-ft. Dont need much more than that. The 4 bolt main 400's are actually weaker because of the material removed by the main bolts.
     
  5. fatdog

    fatdog Registered Member

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    As far as durability goes the 400 is fine. I have run several of these over the years and have had no problems. Took one out of my 71 GMC last fall with 220k on it. Replaced it with a 383 I found in the nickel ads that someone else had built. Mistake! This 383 doesn't have very much power, and the pistons rattle in it. I know the 383 is great, but not this one. Guy I bought it from said it had the Keith Black hyperutectic pistons in it. Anyone else have this problem? Either engine you build will probably be fine so long as its built correctly. I haven't lit it off yet, but I have a fresh long rod 400 sitting in the 71 chev. Here's hoping it doesn't have rattling pistons!
     
  6. Beast388

    Beast388 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Guy I bought it from said it had the Keith Black hyperutectic pistons in it. Anyone else have this problem?

    [/ QUOTE ]

    I have KB pistons in my 388. I have no rattling problems whatsover. Hypereutectic pistons will actually rattle less than forged because forged pistons swell more than hypers when they get warm. Therefore more cylinder wall clearence must be built into the forged piston engine or lock-up may occur.

    If the 383 has a piston rattle problem, someone didn't build it correctly. That may also be why it lacks power.
    /forums/images/graemlins/burb.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/burb.gif
     
  7. Triaged

    Triaged 1/2 ton status

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    Build the 400. Asside from the extra cubes you also un shroud the valves because of the larger bore.
     
  8. Sandman

    Sandman 3/4 ton status Author

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    I had good luck with my 400 for years. Drilling the heads for the steam ports is easy. I just laid the gasket on the head to gigure out where the holes needed to be and then drilled them. It worked well. I over reved it in a mud race and killed it. /forums/images/graemlins/frown.gif
     
  9. ben427

    ben427 1/2 ton status

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    when you drill the steam holes do you just drill as far as the water jacket or what? i was wondering on how to do this so i wouldnt have to pay some one too.
     
  10. Sandman

    Sandman 3/4 ton status Author

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    Yes. They are just small holes that go into the water jacket. Once you do one you'll see it. Its really not that big of a deal. I just used a gasket to get the placing correct. Good luck with it. /forums/images/graemlins/grin.gif
     
  11. Roostr84

    Roostr84 1/2 ton status

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    One of the steam holes is supposed to be on a 45 degree angle. I think I saw a write up this month in one of the chevy mags while i was waiting in line at the store the other day. I wanna say Chevy High Performance was the one. Anyway it is a how too article on drilling the steam holes in non 400 heads.
     
  12. Stroked72Blazer

    Stroked72Blazer 1/2 ton status

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    Guy I bought it from said it had the Keith Black hyperutectic pistons in it. Anyone else have this problem?

    If they are short skirt pistons the pick up this months Hot Rod Mag. There is an article in pit stop that deals with this and gives an example of how you might fix it.
     
  13. fatdog

    fatdog Registered Member

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    Thanks I'll pick up a copy. I'll need to fix it sometime. I really believe whoever built this engine just didn't know enough. I think the real problem (as stated before) is the pistons have improper clearances due to the low thermal expansion properties of the hyperutectic material. It has all the good parts including aftermarket heads &amp; intake but ironically doesn't have as much power as a good stock 350! /forums/images/graemlins/shocked.gif It was a pig in a poke when I bought it anyway. The story goes like this. The 383 was built but before it was installed the guy changed his mind in favor of a big block. It was one of those, (my cousin's uncle's brother who own a a machine shop built it) type of deals /forums/images/graemlins/deal.gif. Really nobody's fault but mine for buying the thing, but I got it for less than I could buy the heads for /forums/images/graemlins/grin.gif, so I took a chance.

    Later, Rob
     
  14. Steve_Chin

    Steve_Chin 1/2 ton status

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    Be careful with the ring gaps in the hypereutectic pistons. KB states in their instructions that the upper ring gap *must* be a large amount greater than the gap for a cast or forged piston due to the thermal isolation of the ring. If the upper rings aren't gapped properly, you could end up with the ring ends merging due to thermal expansion and then galling the cylinder walls.
     
  15. fatdog

    fatdog Registered Member

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    That's a good "heads up" Steve.

    Thanks,

    Rob
     

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