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1967 427c.i. to a 496c.i. Stroker Dilema

Discussion in 'The Garage' started by eighty3seamon, Feb 15, 2006.

  1. eighty3seamon

    eighty3seamon Newbie

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    Hello all, I have acquired a 1967 427c.i. motor, casting number 3869942 which has 2 bolt mains from a passenger car (short deck 9.8"). It is a complete motor with closed chamber, rectangular port, cast iron heads from 1968.

    I have a few questions for you guys:

    1) Can this motor be stroked to 4.25" and bored 0.060" over to make it a 496 c.i. motor?
    2) What is the maximum compression ratio that can be run with the heads?
    3) Am I wasting my time with this block and head combination, and if so, what is a better combination that is affordable?:eek1:

    Thank You!
     
  2. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    i'm no expert, but i would think that 2 bolt mains might be kind of risky. it sounds like you're looking for serious power and more over, torque. i'd question the 2 bolt main. as to your questions, i don't know. sorry dude.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    First things first, i doubt you will be able to stroke it .500" without doing some serious block clearancing.

    You should be able to safely bore the block .060" without any troubles and probably even further with that early block but i would sonic check it first if you wish to go even larger with the bore.

    Rectangal port heads are a no no for a truck unless you are looking for balls out top end with no bottom end. Those heads are just too big for a street motor, they are better suited for a race car where they would really show improvement at much higher RPM's.

    As for compression ratio, in a heavy vehicle such as our rigs i don't like to see compression ratios much over 9:1.

    Ask Burt4x4 about the engine i built for him, he just had it on a chassis dyno making 285hp and 390 ft. lbs. torque at the rear tires. He is very happy with it and it was built very conservatively for a long life.
     
  4. mountainexplorer

    mountainexplorer 1/2 ton status

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    If I remember right, a 496 is a 454 block bored .060 over with a stroker crank. Bored .030 over is a 488. That is what I am under the impression of but don't want to state that as absolute fact since I am no expert.

    I know you can make a 427 using a 454 block and 396 crank. But I'm not too sure on what actual other block differences there may be from a factory 427 block vs a 454 block. I know that a 396 and 402 essentially share the same block, just a 402 has a .030 larger bore than a 396 from the factory. I don't think that's the same though with a 427 block vs 454.

    It's hard to find a 2-bolt main 454 (at least in my case). I've had alot of big blocks over the years pass through my hands, and all were 2-bolt mains. If you can find a 4-bolt BBC it's a nice extra to have, but seems as if the 2-bolt mains can handle quite a bit. I rarely hear about BBC motors that flew apart due to main cap or main bolt failure unless it's some extremely high HP or high rpm motor.
     
  5. eighty3seamon

    eighty3seamon Newbie

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    Thanks guys!! I was thinking about splaying the main caps and make it a 4 bolt. I have heard of this done with the use of 4 bolt main caps, and splaying the block. Also, This is a stock c.i. motor of 427, not a conversion from another block. It is stock 3.76" stroke and 4.25" bore (however it is 0.030" to 0.060" overbore right now)I am not sure of the exact overbore, but if it is 0.060" over, is it possible to go safely past that? the walls are not scored, but they will still need to be honed with a torque plate, so the maximum bore worries me...Should it?
    So is there an overall concensus that there will be a significant amount of machining in the block to go 4.25" stroke, and if so, is there anything other than machine time limiting me from having it done i.e. coolant/oil passages and longevity of the motor being strength??

    Sorry for the longwinded question, but I want serious power (I have seen nearly 700hp done with this stroker kit on pump gas and 12.5:1 compression) from the block.

    Thanks again!!
     
  6. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Have a shop sonic check the block for thickness, this is the only way to know for sure how far it can be safely bored.

    What are your intentions for this engine, race engine or truck stump pulling monster? For a truck you want torque not HP. Also if you are wanting to run pump gas you do not want more than 9.5:1 compression ratio or it will ping on pump gas which kills an engine very fast.
     
  7. hack500

    hack500 1/2 ton status

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    the block that you have now should be able to be stroked and bored to a 496. that block was used for 454's and 427's. up until '75. a 2-bolt mains are good until about 600hp. then you could run a main cap girdle or possible machine it for a 4-bolt setup.
     
  8. DEMON44

    DEMON44 Low-Tech Redneck

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    If you run pump gas in an engine with 12.5:1 CR. It'll be dead in a hurry. No bones about it.
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    A stock stroke 454 crank will hit the inside of a 427 block even though you may think the blocks are the same because of the bore diameter. Trust me, i have first hand experience with that.
     
  10. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    Does the new 496 have a taller deck height than the 454 had? I'm just guessing but maybe the cam has to be moved up in the block to clear the longer stroke? If you plan on turning 6500+ often, I would at least put main studs in it, and if more than that, splay the caps, they will be stronger that way, than a stock 4 bolt. I would think the block could be used, but with much machine work. Maybe a Merlin block would be the way to start.
     
  11. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I'm not sure about the new 496 but building a 496 with a gen-IV block it is a .060" overbore with a .250" longer stroke. I would definately install a set of main studs no matter what you do but as fas as splayed 4 bolt main caps i'm pretty sure that is a small block deal only as every after market 4 bolt cap i've seen for a BBC is a straight bolt pattern not splayded.
     
  12. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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  13. eighty3seamon

    eighty3seamon Newbie

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    Thank you guys!!
     
  14. Blazer X

    Blazer X Registered Member

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    I just built a 496 out of a 74 454 that was bored .060. I used a steel crank, H-beam rods, 9.5 comp., peanut port heads with big valves installed, and slightly larger cam that the GM 502 uses. I run a truck avenger 770, stock ignition, and 3" exhaust. The block needed some machining but guys this is a awesome engine. I run 1 ton drivetrain with 38" boggers on my blazer and this thing will light them up on the street.
     

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