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How much hp and torque now???

Discussion in 'The Garage' started by 87BrnRsd, Jun 25, 2003.

  1. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I have a quick question for yall. I have an 87 K5 with 350 and tbi. I just got the engine re-built and it was bored 30 over. If it had 210 hp from the factory, how much will I gain from the 30 over? I was told only about 5 hp. Also, does anyone know the stock torque on this engine, and how much I gained from the boring? Thanks.
    -Harrison
     
  2. heavy4x4

    heavy4x4 1/2 ton status

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    Stock torque is 300.

    As for the numbers after the re-bore...sorry, but you won't notice much seat-of-the-pants improvements. Only real improvements are what you'll feel from an old, worn-out stocker to a rebuilt stocker.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    If I remember my math correctly, a .030" overbore on a 350 adds a whopping 5CID. Which is why I personally would rather trade that 5CID gain off for a cooler engine, and one that can be rebuilt more times.

    Of course, my block is .030" over too,(*supposedly* needed it to clean up) so there ya go lol.
     
  4. heavy4x4

    heavy4x4 1/2 ton status

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    Alright, I'm ready for a heated debate /forums/images/graemlins/tongue.gif /forums/images/graemlins/smirk.gif So, do tell:
    [ QUOTE ]
    I personally would rather trade that 5CID gain off for a cooler engine

    [/ QUOTE ]

    How do you figure. You're saying that an overbored 350 will run hotter? Maybe you're right, but that doesn't make sense to me. You've still got the same amount of coolant flowing in the same passages (not like siamesed 400 cylinders) and now you've got less block material to cool.

    Educate me please. /forums/images/graemlins/grin.gif
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Less cylinder wall material to absorb/dissipate the heat through, plus the heat applied to the wall isn't constant, so you see "bursts" of heat. More material slows down heat transfer. Keep more heat in the combustion chamber. Not entirely what you want when dealing with emissions, but it's a fine line. Have a motor that ran cool as a cucumber in all conditions at .040" over, took it to .060" when I rebuilt it (didn't know better) and now it CAN'T be kept cool at idle.

    That .030" is probably a negligible difference to a good cooling system, but you are typically talking .060" MAX overbore on an SBC, if you are lucky, so you are halfway to where it's deemed "too thin".

    Aside from that, you also end up with weaker cylinder walls that are more prone to distortion, another reason you see max. overbore limits for engines.
     
  6. heavy4x4

    heavy4x4 1/2 ton status

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    [ QUOTE ]
    Less cylinder wall material to absorb/dissipate the heat through, plus the heat applied to the wall isn't constant, so you see "bursts" of heat. More material slows down heat transfer. Keep more heat in the combustion chamber. Not entirely what you want when dealing with emissions, but it's a fine line. Have a motor that ran cool as a cucumber in all conditions at .040" over, took it to .060" when I rebuilt it (didn't know better) and now it CAN'T be kept cool at idle.

    [/ QUOTE ]

    Gotcha /forums/images/graemlins/thumb.gif

    And yup, I knew that .060 was the "limit" for the reasons you said.

    Thanks Dorian.
     
  7. 1972Blazer

    1972Blazer 1/2 ton status

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    I have run numerous 350 cubic inch engines at .030 .045 and .060 and have never hear of problems with overheating. If you are having problems with overheating it is probably caused by something else you did or did not do during the rebuild. I have done the same with the siemesed bore 400 cubic inch blocks without any problems due to overheating. When you build an engine the stock cooling system is probably old and not up to the task of cooling any more anyway. Try at least having the radiator steamed out every time you change an engine or you could always upgrade your cooling system to a one out of a Big Block.
     
  8. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I agree with 1972Blazer. The owner of the engine rebuild shop I took mine too said that it is an absolute must to boil the radiator out. And so did the guy at the radiator shop, and the service manager at my local chevy dealership, (who, not to mention is a friend of mine). Not boiling out the radiator would be like using the old oil pump and screen and wondering why the oil pressure sucks.
    -Harrison
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    FWIW, I had the radiator rebuilt right before I swapped the motor back in, so the culprit was the .020" (more) overbore, nothing else. Went back into the same vehicle with the same accessories as before.
     
  10. 1972Blazer

    1972Blazer 1/2 ton status

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    We are only talking about 20/1000 of an inch, what could that kind of bore thickness have on cooling. I have heard this before but have never seen anyone prove that it would make a difference. Problems with cooling can be traced to alot of things such as air/fuel mixture, heads, valve adjustment, timing, cam profile, exhaust, cooling system. If the engine is bored beyond the recommended amount it can then have thin spots that will in turn be hot spots during operation causing cooling issues. The 400 cubic inch engine are harder to keep cool due to the siemesed cylinder walls, the coolant does not circulate completely. All 1st generation design Chevrolet small block engines are considered completely safe to .060, you can go beyond this if you have the block sonic tested. I just dont understand the train of thought here, that it would be caused by an overbore of such a small amount?
     
  11. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I'm not saying your wrong, because I dont really know much about this. But since you had the radiator rebuilt and it still didnt cool, maybe the shop that rebuilt the engine (if you took it to a shop), bored it more than they said. Some shops will bore engines 80 over just to get away with keeping a bad block. But I dont know.
    P.S. Dyeager, are you the one that wanted the 3.42 gears from my 10 bolts? If so, and you still do, I will probably be taking the axles out in the next month or two, and can sell you stuff then. Let me know. /forums/images/graemlins/thumb.gif
    -Harrison
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    maybe the shop that rebuilt the engine (if you took it to a shop)

    [/ QUOTE ]

    Nope, pulled it apart myself (.040" over) and reassembled it myself (.060").

    The more metal you have the more heat that can be absorbed BEFORE it is passed to the coolant. Without a "barrier" (the iron) the heat is passed immediately to the coolant. This is a problem you would tend to see with lowered cooling system effectiveness, such as idling. Too little coolant, moving too slowly, causes even more problems.

    If combustion chamber heat production was constant, then this wouldn't be a concern. But in a typical engine, the load is never constant, so heat generation varies greatly. Just imagine a drop of water on a sheet of metal, and increase the sheet of metal in thickness .030" or .060", whatever. Pass a torch underneath each one. Which will vaporize the water first? Of course both will eventually vaporize, but the thicker metal will take longer obviously. For this not to be the case, an engine would have to be "maxing out" heat absorbtion of the cylinder wall at all times.

    Siamesed bores apparently do have more of a problem with cooling/wall thickness than other engines, but cylinder wall mass is still a factor.
     

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