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Thread: Displacement increase?

  1. #1

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    Displacement increase?

    Ok, I'm good at problem solving, fabrication, and general fiddling. What I'm NOT good at is numbers and theory-crafting.

    I am going to get off my ass as soon as the company sends my tax paper and get my return on the way so I can get some shit done. I need to finish the top end of this engine ASAP so I can get the carb jetted and tuned.

    So, my plan:

    Gonna get the new cam and send it in for a higher duration grind and install roller rockers. I would LIKE to go ahead and purchase a set of Starion stainless valves (1mm bigger than stock) and send my head back to Rick's to port the new valves in and put in some stiffer springs. When I put the new goodies in, the head gets studs instead of bolts, and I plan to purchase one of the copper billet head gaskets one of our members linked a while back.


    The conundrum:

    I want to keep and generate maximum torque with this engine, Hp is nice, but not the focus. Were I to go with a thicker head gasket and increase my displacement a bit, would that drop the Hp a bit and bump the torque? I'm no engine builder, despite being capable of dangerous things with an engine (mostly leading to dead engines). If I were to go thicker, how much? How would I calculate the changes, and how do I determine what the outcome would be?


    So, obviously I'm mostly clueless as to what I'm doing. I know what I want to happen, just not sure how.

  2. #2


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    General rule of thumb is Bore= Torque, Stroke= HP. so a .030 overbore will produce more torque then a stock piston everything else being the same.If you ever take apart a diesel you will see it's a larger bore with a shorter stroke vs a gas engine of the same displacement that has a longer stroke and a smaller bore.

  3. #3

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    Alright, so I'm already .060 over...I think...was bored as far as he could to take out a bad score in the #3 cylinder, said it couldn't go any further without sleeving the bore. I cannot find the original paperwork for the short block (whole damn folder from the first rebuild is MIA). Sounds like I should just stick with OEM gasket thickness, OR find my valve clearance and go a bit thinner for higher compression? Engine is already running flat-top pistons, but the crank was not stroked.

    Have already found I need to use mid-grade or premium for the damn engine to run right...ain't gonna hurt nothing if I bump it a bit further.

  4. #4



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    You would go with a thicker head gasket if the deck and head was plained. This will keep the same distance between the cam and crank center lines. other wise the cam timing is retarded and compression is increased.
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  5. #5



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    If you go with a thinner head gasket or shaved the head, you will need to notch the top of the pistons or change to starquest dished pistons to clear the valves.
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  6. #6


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    another aspect of Torque vs horsepower is intake runner length. long runners = Torque, short runners = HP. I'm not sure you have many Options on Intakes with these trucks unless you fabricate.

  7. #7

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    your talking about plenum volume if i'm not mistaken.

  8. #8


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    Nope, Runner length

  9. #9


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    Quote Originally Posted by LSR Mike View Post
    Nope, Runner length
    http://auto.howstuffworks.com/question517.htm

    not being an ass, just some reference info. Longer runners would affect Plenum volume but tuned runners are a different science.
    I used to have a Lincoln Mark VIII which had a dual runner system, long runners for low rpm with an automatic switch to short runners at high RPM.
    I loved that Car...4.6L 4 CAM Hemi

  10. #10



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    My Blackwood has a slightly different system for tuning the runners - it has a set of flaps in the intake runners that move dependant on the throttle position. Its the reason the motor has a torque peak @ 2750 rpm - and its a 4 valve motor. Makes it an exceptional tow vehicle, and 13 - 14 MPG towing @ 70 mph.
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  11. #11

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    i did not know that about the runner length of the intake manifold. good to know info. i learn something new on here all the time.

  12. #12

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    Interesting read, thank you. Not sure I wanna fiddle with something like that, but like PR said, learned something new!

  13. #13

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    Your best bet for torque is to have the crank re-stroked, or (I think Crower sells new ones).
    I had mine stroked to 4.11" using a turbo block bored .100" over.
    Right at 2.9L, amazing low end torque !!!

  14. #14


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    Holy thread resurrection!

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