482 comp. ratio help

Discussion in 'Street/strip 400/430/455' started by B-rock, Oct 21, 2019.

  1. B-rock

    B-rock Well-Known Member

    http://www.diamondracing.net/tools/
    Just got my pistons in the mail.
    using that tool. Im coming up with a higher then expected static comp ratio. wanting to double check my numbers. I called diamond and confirmed my piston numbers are correct.

    head gaskets are felpro 1125. This might change depending on my comp. ratio.

    the engine is the 482 recipie with diamond pistons, molnar rods.
    TA stage 2 SE heads.

    is this correct or did I enter some wrong numbers?
     

    Attached Files:

    Last edited: Oct 21, 2019
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Are you sure about your head chamber cc? 64?
     
  3. Bens99gtp

    Bens99gtp Well-Known Member

    10.8 should be pump gas friendly with AL heads. Dont go crazy on the timing. If need you should be able to manipulate your dcr with cam selection
     
  4. B-rock

    B-rock Well-Known Member

  5. B-rock

    B-rock Well-Known Member

    The plan was 10.3. And I was happy with 10 to 10.5. Range.
     
  6. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Try the calculator with these;

    https://www.summitracing.com/parts/cgt-c5755-045/overview/make/buick

    Or machine the block so the pistons are .005" in the hole and see what you get, .045" is at the top of the "good quench" spectrum so still a good target. That should give you maybe a .2 reduction if you don't like the gaskets in the link?
     
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  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Stock block deck height for the 455 is 10.570 not 10.550 unless your block has been decked that amount?
     
  8. B-rock

    B-rock Well-Known Member

    the 10.550 should be after the deck is shaved .20 to clean it up. This will also give the zero deck. If I’m understanding this all correctly.
     
  9. B-rock

    B-rock Well-Known Member


    That head gasket brings me down to 10.37 Thats just where I want to be! Looks like I have a couple felpro headgaskets to sell.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, my point is it hasn't been machined yet, correct? So you have some lead way as far as how much the piston is in the hole if you want to lower your compression. You really should decide on a cam. 11:1 SCR may be just fine depending on the cam.
     
  11. B-rock

    B-rock Well-Known Member

    Ahh I see, But that would remove my zero deck that I was understanding was so important to have? And yes, it's absolutely down to needing to pick a cam now. I need to make some time for that.
     
  12. Bens99gtp

    Bens99gtp Well-Known Member

    The .020 is a safe baseline number, your block might clean up and square up without that much needing to cut ome off. So if you can square up and clean up while still being .010 down your gaskets might work well.

    This is prime example as to why having an idea plan is great . But leave it open and flexible and dont go buying too many parts too soon. You have to almost actually let the block almost dictate the build and the get the parts needed to fit the block.

    If the block gets machined first I'm sure piston CD height could be adjusted b4 purchased to fix as well
     
    Last edited: Oct 21, 2019
    B-rock likes this.
  13. B-rock

    B-rock Well-Known Member

    Thats some great info there. Thank you!
     
  14. Bens99gtp

    Bens99gtp Well-Known Member

    I know it's tough to wait on a build, one thing we all want to know is price b4 starting we all have a budget to stay within.

    But sometimes that not the best way to start, especially if you are trying to target something very specific
     
    B-rock likes this.
  15. No Lift

    No Lift Platinum Level Contributor

    Increased stroke will add compression ratio so if you calculate with a shorter 3.90 stroke it will be noticeably lower.

    I've been running 10.9 compression, O deck, and aluminum heads on pump gas with no problem. You need to run at least 1/2 point or more compression just to make up for the heat loss through the aluminum heads. I'd keep the close to 0 deck(.010" or less) for the best quench and as long as you don't want a stock-like idle from the cam you should be fine. I would think that you go for a DCR of 8-8.5 because of the heads. Keep the timing curve conservative, slower and max timing. Decent gears and a good converter will keep the engine from lugging. Plus a good cooling system. 92-93 octane.

    Increasing the stroke increases piston speed and I thought I read that it lessens the time the piston is at TDC therefore reducing its' tendency to knock.
     
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  16. B-rock

    B-rock Well-Known Member

    Good points. I have 350 gears in a ford 9" right now. The converter is a tri shield unit that will be ??? I forget the numbers but im guessing without looking it up but 2500??? Id like a decent idle quality but im not picky about that. will be running hydroboost brakes so Vacuum is not an issue. Im trying to swing the hydraulic roller cam too. But just that cam brings in a lot of cost and im trying to determine if the Return on investment of a roller is there.
     
  17. Bens99gtp

    Bens99gtp Well-Known Member

    If you already have pistons coming you can drop back to 3.9 stroke......be way in hole then
     
  18. B-rock

    B-rock Well-Known Member

    I have Pistons in hand and rods are on there way. This is the Tri shield performance 482 recipe that so many guys here are running.
     
  19. Bens99gtp

    Bens99gtp Well-Known Member

    Sounds like it should end up being a mean machine. Even if as cast heads that should be a very low 11 second street car. If the heads are ported 10s should be easy to get
     
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You could have adjusted the piston valve reliefs to compensate. My TA stage 1SE heads had .040 off, and the chambers ended up at 61cc. My pistons had 30cc in them to get me to 10.5:1 with 0 deck. Maybe you can exchange the pistons?
     

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