Target compression ratio A/J

Discussion in 'Big Block A body Tech' started by 1930, Apr 21, 2017.

  1. 1930

    1930 Well-Known Member

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    I hear alot of different views on what you can and cant do on pump gas. Without getting too long winded I know there are alot of things that supposedly cant be done as far as exceeding a certain amount of compression. I dont believe that the limits are set in stone.

    Here is where Im at with my 440 as far as how far down in the hole.

    I dont know still though how the deck is in relation to the crank, I mean there are alot of variances here especially one side of the block compared to the other and can that be contributed to piston height, connecting rod variances, crankshaft abnormalities, casting/deck height abnormalities or the most likely culprit a combination of it all.

    Without getting all nascar here Id still like to do it right.

    The block has been bored .060 over, new pistons, crank turned, obviously all new bearings ect ect. Im not in nearly as deep as a guy that plans to race but Im not half assing anything that Im aware of either so far and so Id like to take advantage of every little trade secret I can to get the most out of this that I can.

    Talking with the guy thats gonna cut my cam we figured in a zero deck clearance and so with that in mind whats the best way to get there at this point, what way makes the most sense?

    I know I am missing important information like head gasket thickness ( I dont have one yet so I am open to anything ) valve relief CCs ( which I can call and get tomm ) Aluminum head CCs ( Im still waiting on my heads, should be here in a few days, supposed to be 84 CCs and Im pretty sure thats what they are gonna be ) Deck thickness ( I dont know yet where thats gonna end up ) stroke has changed since the cranks been cut but maybe the difference is irrelevant.



    I know I scribbled out some info so just in case it cant be read cylinders are down in the hole as follows.

    1- .014 2- .023

    3 - .013 4- .022

    5- .015 6- .025

    7- .015 8- .024

    Picture 327.jpg

    Picture 328.jpg

    Picture 329.jpg
     
    Last edited: Apr 21, 2017
  2. famous bob

    famous bob mopar misfit

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    Why would the stroke be changed , just having the crank turned? Unless u had it offset ground.
     
  3. 1930

    1930 Well-Known Member

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    I was just throwin it out there that it had been done buy your right, I wasnt thinking
     
  4. bOb shingler

    bOb shingler Well-Known Member

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    you need to have the even side decked .010" to even the decks up. the small difference in the hole won't matter but the .010" will.
     
  5. Marcohotrod

    Marcohotrod Well-Known Member

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    why does dial indicator say .068" ? I would throw a rod and piston from one side in to the other side, just in case you have the short ones all on 1 side (probably the block is the reason 1 side averages .010" different) Then just cut 1 head .010" to even out the compression ratio. what is the piston part number-look up valve notch cc. how much compression ratio you can run depends on many factors! closed chamber heads? run a thin gasket to get some quench
     
  6. IQ52

    IQ52 Well-Known Member

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    Zero deck huh? As your pistons are, cut the odd side .013" and the even side .022"

    Now you have as deck heights.........

    1) .001 2) .001

    3) .000 4) .000

    5) .002 6) .003

    7) .002 6) .002

    Then with an 84cc combustion chamber, 7cc valve reliefs, .039 8519PT1 head gasket, you have for compression ratios........

    1) 10.13 2) 10.13

    3) 10.15 4) 10.15

    5) 10.11 6) 10.09

    7) 10.11 8) 10.11

    It's unlikely that the combustion chambers will all be 84cc but, still, close enough.
     
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    • 1930

      1930 Well-Known Member

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      It just wasnt at the top when I took the photo.

      I may be mistaken but I thought pistons cant be switched around like that on a BB cause of pin offset.Hopefully someone can confirm or deny that.
      Would you explain to me what you meant by this if anything Quote: Zero deck huh?

      Sounds like a problem somewhere to me.

      Thanks for the figures.

      I measured small block set of Edelbrock heads and unless there is a different way to measure the CCs that is more accurate than what I had done then Ill say that the small block heads came up showing same combustion number sizes.
       
    • 1930

      1930 Well-Known Member

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      Reversing the stock OEM piston in the bores will make them slap when idling cold and probably slap when warmed up. This is a old trick done by drag racers back a long time ago in the old Jr Stock days, a long time ago.
      What it does is reverse the wrist pin offse
       
    • IQ52

      IQ52 Well-Known Member

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      I was acknowledging your desire to get zero deck, nothing negative. I'll try not to get "all nascar" even though my dad used to build engines in NASCAR many years ago.
       
      Last edited: Apr 21, 2017
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      • 1930

        1930 Well-Known Member

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        You were fortunate to be around that as a child, my dad was a cabinet maker, fine furniture. He was very good at what he did ( cause he cared about what he did ) as Im sure your dad was as well. ( cause he worked in Nascar )

        I grew up thinking that I would follow in his footsteps but seeing the struggles he endured cause it was cheaper to go buy something at the nearest dept store turned me away from that as a teenager.

        I hope you got to spent your life doing what you wanted to do as our fathers did.

        Im a bodyman and I wouldnt have it any other way.

        My father passed away in the mid eighties and there still isnt a day that dosent go by that I dont regret telling him how much I admired him. His name was Martin Anderson. I was hell in wheels :(
         
        Last edited: Apr 21, 2017
      • AJ/FormS

        AJ/FormS FormulaS clone 367-3.55s 3.09-1.92-1.40-1.09-.78od

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        Wait!
        Are you saying the cam has already been ordered?

        Are those aluminum heads closed chamber heads? If yes, then IQ52 has got a recipe for you in post #6.
        But if your cam has already been ordered, And with Scr of just 10.15, Your Dcr may get to be in the basement. This SCr will take a fairly mild cam to be a fun streeter.If the Dcr falls too low, you will be wanting a higher stall TC to get moving.Low DCrs tend to be soggy out of the gate. Aluminum heads suck heat out of the chamber. Heat that coulda been used to propel the vehicle. This lost heat needs to be compensated for with about a half a point of Dcr. This may take additional Scr to get. So if your cam is already on the way, you may have gotten ahead of yourself.
        But if you are building a track engine, then this hardly matters cuz your hi-stall TC is gonna blast your car right thru and past the soggy bottom end.
        AJs ramblings;
        If I had a BB for my streeter, I'd want to run 3.23s. and a stock-type stall(2200 to 2400).And that would take a strong bottom end torque supply. And that would mean a conservative cam,and a matching Dcr.In this way, first gear would be good for close to 60mph, and 3.23s puts hiway cruising on the table. I would run a small vacuum secondary or AVS-type carb that I can bring the secondaries in as early as I want to, or as late as I need to. A double pumper will just destroy the tires. A spread-bore would be even better.In this way, I would attempt to not blow the tires away on every hard take-off. As a streeter I don't need a big cam, cuz there's that speed limit thing about 5 seconds after take-off.So I can't use second or third. And a 7000 rpm redline is kindof crazy if hit 60 at 6200.

        3.23s will hit 60 at 6200 with a 2.45 low,and 5% slip and 27 inch tires. This would work well with a 110*cam that peaks around 5400, or a 108* cam that peaks at 5500, or a 106*cam that peaks around 5600. Or a 104*cam that peaks around 5700.These are pretty small cams.
        In an A-body, I would go for the tightest LSA cam I could get to make maximum power, with a very rapid fall-off after the peak, cuz I don't need to rev to the moon. Look; with the BB,my tires are gonna be smoking anyway, so I don't need more low-end torque. I need a top end rush from 35mph to 60 so gimme that tight LSA.

        If you have looked at BB dyno curves with 110 cams peaking at 5800, you might see the power curve nearly flat from 1500 before the peak, and stretching nearly 1200 after the peak. For a streeter, IMO that is crazy. I have to stop at 65mph or risk loosing; my car, my license, or both. So if my power curve extends to 7500, how does that help me? No if the engine gets me to 60/65 at 6200 then I don't care if 200 rpm later the curve hits a wall and drops to zero!, Right? So gimme that tight LSA,that will focus the power to a higher number over a more narrow rpm band.
        So then IMO a small cam on a tight LSA is the secret to a BB streeters nightmare. Then put the power in the heads.
        If I ever put a new cam in my Barracuda 367, it's gonna be something like 262/272/104. A roller. With mega-lift! And ported-for-street, Magnum heads. And a spreadbore. And it's gonna run on the edge of detonation with 87E10. So, I'm gonna run 87 in the front bowl, and 91 in the back dumps, and see what happens,lol.And Ima gonna gear it to hit 62mph (the speed limit here), just after the power peak. And I don't care if it takes 4 minutes to do the quarter mile.
        Then Ima gonna work on the suspension until it pulls the wheels on the asphalt, in front of my house! And then Ima gonna tune that badboy, to get mileage like nobody believes. Hyup, I got overdrive.
        Dreaming is so much good therapy.
         
        Last edited: Apr 21, 2017
      • yellow rose

        yellow rose Doctor of Thinkology.

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        That's the first time I ever heard going "all nascar" on some one. That's a good one right there. I love it!
         
      • IQ52

        IQ52 Well-Known Member

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      • 1930

        1930 Well-Known Member

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        Closed chamber 84 CC. I have not ordered the cam yet, havent heard back from cam builder yet with his thoughts, this engine Ive decided is gonna go in the 6000 pound 4 wheel drive truck I mentioned to you, Im gonna put the 340 in the 2 wheel drive.

        This trucks has a 4 spd with granny gear, I gave what specs were asked of me to the cam guy. hes the one that suggested target zero deck ( if I understood correctly )

        One thing that Id like to know is why does the story change on whats first, alot of people say cam is first, other people say other things. Why cant everyone get together on this one?
         
      • 1930

        1930 Well-Known Member

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        Ive got a 340 build going on in the small block forum. I ccd the performer RPM heads and every single cylinder was identical. No variations. The heads ........now that I think of it had port work done to them, I dont know by whom, maybe they did chamber work as well but I didnt see any signs.

        Cant open the links till I get home cause my internet is too slow at the shop but Ill check them out
         
      • AJ/FormS

        AJ/FormS FormulaS clone 367-3.55s 3.09-1.92-1.40-1.09-.78od

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        That frieburger test was done with a 260@050 tappet lift. Wouldn't that be about 305 or more advertised duration? The math on 305* makes a Dcr of 7.7 or something.
        I understand that the test looks reasonable and fair, but
        IMO that is not representative of the typical street build.
        We need to get a test with a much more sane street cam, and a Dcr of about 9.0, and watch which heads burn what gas and at what timing.I think then things will dramatically change.
        Or alternatively, pick a cam in the 220 to 230 range, and limit the timing to 35*, then adjust the Scr until they hit detonation on 89.Then calculate the Dcrs. Now that's a test I'd like to see.
        If anything,;Frieburgers test is a testament to the aluminum heads not losing power when Dcr-limited to 7.7! Now, just try and drive that 7.7aluminum headed beast with normal street gears and a street stall TC.
        As always, the dyno is a WOT snapshot of, what basically amounts to a race engine;not a street combo.
        And for anyone who trys to run 110*F on a streeter, with a carb, well,let's just see how long, and how many miles, that engine lasts. You may need a separate 15hp small engine to power up the fan.
        And in a racecar, just how are you gonna control that temp from waiting in the line to blasting off, run after run?
        It's a nice number to know but IMO so what.
        Anyway; that'd my opinion
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        Nope. I'm 255 @ .050 and the seat to seat is 281 so I doubt that cam at 260 is as slow as 305. I probably should read the article. Crap.
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        Because people don't always skin a cat the same way. If I have the choice, the LAST thing I buy is the cam. I start with displacement/geometry. Then is RPM range. Then compression ratio. Then induction. Then I get the cam that fits all that.

        You may not always have the option to do it that way, but it's how I like to do it when I can.
         
      • AJ/FormS

        AJ/FormS FormulaS clone 367-3.55s 3.09-1.92-1.40-1.09-.78od

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        It is cam first. But the cam has to fit the application. And then the engine has to more or less be built around the cam.
        You have already chosen all the components so now we have to fit the cam to the components.And the biggest reason is to not end up with a soggy bottom end that demands a 3500TC and 4.30 gears, and burns gas at an alarming rate; so much so that your 15,000 or 20,000 dollar or more machine, spends most of it's life parked.Phew, that was a mouthful.
        See; at just 10.15 Scr it will be easy to overcam it now for street use in a 6000 pound truck, and run into detonation at WOT. But it will be almost as easy under-cam it and run into detonation at PT;part throttle.

        I'm so glad you decided to put the 440 in the heavy machine.
        >Have you stated your goals with this truck yet? Is it to have a first gear blast-off, and then sit back and mellow out? Is this the truck with 3.55s and 33" tires and the NP435? Have you figured out the gear ratios in that badboy tranny yet? Is it the 4.56-2.28-3.31-1.00 unit?
        If this is right, then the Final-Drive TM(torque multiplication)ratio,in first gear , corrected to a 24 inch tire, is 4.56 x 3.55 x 12/(.5x33)=11.77. This is a huge amount of TM for a 440. Your bottom end would have to be pretty soggy for you to notice it.
        On the other hand, this ratio will be revved out by 33mph at 5500. The rpm drop into second will be 2.28/4.56 = 50%, so 5500x .5=2750. This is pretty far down in the rpm band so your cam selection is gonna have to take that into account. Your typical 240@050,badboy idle,440cam is gonna be drowning at 2750, so it's kindof game over for the combo.
        So, with that 240* cam you will have to rev it some more in first, to have something to work with in second gear. The problem I see is that the peak-torque may not come around until 4200, and your engine is not gonna want to spin to 8400, to get it. So the big cam idea you are gonna have to put to rest. Or put to rest any notions of rapid transit in any other gear until the revs get up there. Or slip the crap outta the clutch until the clutch dies.
        So what is the answer?
        The answer is to build an engine that can work with those tranny ratios. That means to build for torque, and forget about the fast way home. YTou have got to satisfy that tranny.
        Ok so what to do? Well it starts with figuring out how to build a super wide torque band to satisfy that 50% 1-2 split. Typically the torque peak rpm comes in at about 75% of the power peak .So if peak power is at 6000, the torque peak might be at 4500. A better way to think of this is that the power peak rpm will be 1.33 times the torque peak. So if we want a torque peak at say 3600, then the power peak might be at 3600x1.33=4800.
        >So now, if we rev the engine to 4800 plus say 10%(so5300) in first, then the Rs will drop to 2650 going into second. But if we somehow flatten the power peak so that we can rev it to say 5800, then the Rs will drop to 2900. That's getting close to 3600/the torque peak, and I'm betting, that a combo like this will be pulling pretty hard at 2900 already.
        >So, for you, to continue accelerating in second gear, the answer is to build a torque monster, that has a long flat hp curve from 4800 to 5800 say; we don't really care about the specific number. But it has to make monster torque from say 1500/2000 (where you drop the clutch),and up. This to continue accelerating in second gear, with those 3.55s.
        If you don't care about second gear, then you are free to choose any cam your engine can be set up to handle. So if you want a raunchy idle, then the 240* or more cam is your baby, if you got the compression to handle it.But I don't think you do.
        The 240*cam is about 284/292/108. With a 66* ICA this sets your Dcr to 7.98@160psi, with that 10.15Scr. But you don't want this 108 cam It makes peaky power and steals the torque away from the bottom. What you need is a 114* LSA or more cam. This,at 10.15Scr and its 72* ICA, sets the Dcr to 7.56@149psi, not nearly enough pressure for what you want to do.
        If you want to run that cam, 284/292/114+4, and have a stronk blast-off, with aluminum heads, then your cylinder pressure will need to be in excess of 165psi and pushing 180psi will be better. 11.3Scr will get you 170psi@8.39Dcr, kindof middle of the road; this to run that 284/292/114+4 cam.
        So; how do we go from 10.15 to 11.3? The difference is 11cc.There is only one way; pistons.
        Now go back to the opening statement."It is cam first. But the cam has to fit the application. And then the engine has to more or less be built around the cam."

        Now, I'm not suggesting that the 240 cam is the best cam for you, cuz I don't read in this thread what you are up to. I kindof guessed. But the point is; the cam has to fit the application, and that tranny is severely restricting your options. Unless you are happy with a zero to 33mph blast-off and D-o-n-e.

        Now, all you BB fellas and builders please chime in and school me, cuz I have no BB experience.please Be gentle .....lol
         
        Last edited: Apr 21, 2017
      • 1930

        1930 Well-Known Member

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        Goal with the truck is something to take ( drive ) to shows, turn alot of heads and park, I have a small bodyshop, I love what I do even after 30 years, I restored the truck to very nice condition and Id like to talk with people who have similar interests and hopefully draw some attention to my handiwork which will allow me to stay in business regardless of the fact that Im not the cheapest guy out there which seems to be what everyone is after these days.

        Yes 3.55s, 33 and I will get the tranny gear ratios, Id think they would be in my FSM but Ive never looked.

        Ok so nothing more needs to be done at this point or nothing more can be done at this point with the block? It sounds like I need to just disassemble it and get it back to the machine shop on Monday to get the deck cut as IQ pointed out above?

        Im trying to stay clear of all the things I could have or should have done after the fact cause I have time now to do these things no problem.

        Unless something else is suggested than its off to the machine shop on Monday to drop this back off. Thanks for everyones input
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        I didn't want to read all this because my birth day is coming in September and I didn't want to miss it...are you saying you pick a cam and build around it?

        If so, you been looking at your belly button too long.
         
      • sireland67

        sireland67 Well-Known Member

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        NP435 trans.
        The very first time my wife drove my truck, she moved furniture for a friend of hers, when the wife came home she said "it did not take me very long to figure out 1st gear was useless".
        I never asked how high she revved the old truck, but it started blowing some blue smoke after that....
         
      • Marcohotrod

        Marcohotrod Well-Known Member

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        you can cut the block, or cut 1 head .010" , and use thin head gaskets, the engine will not know the difference
         
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        • MOPAROFFICIAL

          MOPAROFFICIAL Well-Known Member

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          @ 10.1 static... an ivc of around 54 , dynamic roughly 8.5 175psi would work nice imo and will run 89 octane...but never leave you hurting if the gas is crummy.
          I've run as high as 8.88 dynamic on 91 octane, if the gas ain't fresh it will occasionally run on a second when you turn the key off...If I use STP/Lucas octane boost, no run on....if I out 100 in it , smooth and deepens the exhaust note...so I consider 8.88 the MAX for MY COMBO....it varies from build to build/parts combo what the limit is....so thats why I never try and say "this IS the max ,period" I like to say "ive run as high as" or "run" this dynamic.
          You could push the dynamic up high...but do you need to is the question.
           
        • 1930

          1930 Well-Known Member

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          I like this idea, not saying its the way Im gonna go but to me it makes sense.

          Some of this is above my pay grade ( I do not understand ) but thanks, every post gives me a little to think about