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  • 2 Post By techinspector1
  • 1 Post By new2oldschool

Thread: 350 small block advice
          
   
   

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  1. #1
    new2oldschool's Avatar
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    Smile 350 small block advice

     



    hello everyone im pretty new to the hot rod scene. picked up a nice 4 bolt main small block 350 that already been bored 30 over which is in great condition and just needs to be honed. I want to build this engine with a relative bullet proof bottom end and around 400hp to drop in a 1952 chevy 3100 step side. I also have a set of camel hump heads what im not sure is the right crank, cam, rods and pistons the whole 9 yards. id like to stay around 2000 dollars to build just the engine any help and ideas would be very helpful

  2. #2
    glennsexton's Avatar
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    Welcome!

    Love those old Chevy and Jimmy pickups. I'd stay away from the camel hump if possible.

    Ya might want to peruse this thread.. Rebuild Help and advice !

    Regards,
    Glenn
    "Where the people fear the government you have tyranny. Where the government fears the people you have liberty." John Basil Barnhil

  3. #3
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    I looked at that post already and its not getting through to me. when I look at cranks or comp cams theres so many variables that I have no idea about so I thought id reach out on here

  4. #4
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    Let me see if I can help you out here.....

    Cylinder heads....
    Cast iron......used where cost is a factor and weight is not a consideration. Both factory OEM heads and aftermarket heads can be found in cast iron.
    Any type head gasket of any thickness can be used with an iron head.
    Cast aluminum.....used where cost is not a factor and weight is a consideration. Both factory OEM heads and aftermarket heads can be found in cast aluminum. Use head gaskets with a pre-flattened fire ring to prevent brinelling of the aluminum (making a circular groove in the face of the cylinder head). It is considered by many as advantageous to use a composition gasket rather than a shim gasket, to allow a little movement of the aluminum when it has to get along with an iron block (dissimilar metals grow and shrink at different rates as the heat and cool and you should allow a little "play" between the block and heads).

    Vortec versus Non-Vortec.
    GM used the Vortec name on quite a lot of engines over a period of time, but when we talk about Vortec heads, we are talking about a certain design with raised intake passages and state of the art combustion chamber design that was used on pickup trucks and vans from 1996 through 2002 on 350 motors called L31 5700 Vortec motors. The cylinder head of choice when building a budget street motor is the Regular Production Order (RPO) L31 head, sold over the counter under GM casting numbers 12558060 and 10239906. The 906 heads were used in the heavy duty vehicles and have hard exhaust seats installed. Some fellows say this disrupts flow and others say baloney, they both flow the same. One thing we can all agree on....the L31 heads flow better than any other Chevy production cast iron head. (they are light years beyond the camel hump heads of the 60's, 70's and 80's, which will procuce only around 300-350 hp at 9.5:1 static compression ratio.) 9.5:1 is considered by most to be the upper limit of SCR to use with iron heads on pump gas. 10.5:1 is considered to be the upper limit of SCR to use with aluminum heads on pump gas.

    Vortec Cylinder Heads
    https://sdparts.com/details/gm-perfo...parts/12558060
    http://www.crankshaftcoalition.com/w..._cylinder_head

    Valve lift limit on these heads with stock components is ~0.425". The fellows who tell you that they will support more lift with stock components have not taken into consideration that there needs to be a safety margin of ~0.060" between the bottom of the valve retainer and the top of the valve guide seal. You can change out springs and retainers and achieve more lift though. Production heads use "rail rockers" to position the rocker on the valve stem tip, rather than guide plates. Use one or the other, rail rockers or guide plates. You cannot use both.

    There are other factors that help to determine which heads you use. Intake runner volume in cc's and exhaust runner volume in cc's and combustion chamber volume in cc's. Intake runner volume......will determine the speed of the mixture through the runner before it encounters the intake valve. A small runner will speed up the mixture through the runner and pack the cylinder better on the proper size motor, but it may restrict flow at higher rpm's. A larger runner may support flow at higher rpm's, but may not support mixture speed at lower rpm's. In other words, a 383 with hump heads will be too restrictive for high rpm flow. If you want to build a towing motor for low rpm's, they will work great. If you want to go drag racing, they will be the weak link in your combination. For a street motor, you want to use 1/2 your total displacement as a guide for intake runner volume. (a 383 would like 190-195 cc's generally speaking). If you want to be impressed, look at dyno tests on a 383 with AFR 195 heads.

    The combustion chamber volume has to be added to the piston crown volume and other displacements (piston deck height volume, head gasket volume and cylinder volume to determine static compression ratio. You cannot intelligently choose a camshaft for a motor until you know the static compression ratio.

    No matter the type of build you decide to go with, you should make sure the cylinder block is a valid player before throwing parts at it. The main bearing bore needs to be round and parallel and the block decks need to the same measurement from each corner of the block deck to the centerline of the main bearing bore. Usually, a fellow will choose the stack of parts he will use, then cut the block decks to achieve a certain piston deck height and a certain gasket thickness to reach a desired squish.
    The stack is the total of parts to be used. Let's say we are going to build a 355. The piston would be 1.560" compression height, the rod would be 5.700" in length and the radius of the crankshaft would be 1.740". Total these dimensions up and find 9.000". The block deck height (measurement from the centerline of the main bearing bore to the flat surface of the block deck where the heads bolt on) from the factory is ~9.025", so if we installed a stack of 9.000" in a 9.025" block, the piston would be down in the bore by 0.025" (twenty five thousandths) of an inch. If we used a conventional composition gasket at 0.040" (forty thousandths of an inch) thickness, then we would have a squish of 0.065" (sixty five thousandths of an inch). Since a squish of 0.035" to 0.045" is ideal for a 355, we would need to reduce the height of the block from 9.025" to 9.000" so that the stack of parts would be flush with the block decks with the piston at top dead center. This would allow us to use a 0.040" head gasket thickness to produce a squish of 0.040".

    I'm only touching the surface here, but maybe what I have written will prod you to do some more reading and learning on your own so that you can put together a motor that will do what you want it to do.
    Last edited by techinspector1; 12-04-2013 at 04:34 PM.
    NTFDAY and glennsexton like this.
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  5. #5
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    wow thats alot of info and i thank you for the time spent typing that in for me and i will take your advice and do more research and make sure i cross my i's and dot my t's before i spend any money my block will sit just fine in its submerged trans fluid bath so im in no hurry
    NTFDAY likes this.

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