400 Non Stroker Build

Big Block A body Tech

  1. Bronson77

    Bronson77 Active Member

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    I have a 76 400 I’m thinking about dropping in a 71 C-body. The motor needs rebuilt. I would like to know what kind of power I could realistically make with this.

    Keith Black makes pistons I can use to help raise compression correct? Say .030 400 pistons. I’ve seen some pistons but most are for strokers.
    I would also probably run stealth heads. I want straight plugs. I have a Edelbrock DP4B intake so I would use that. Would also install a cam etc.... I would also gear it with say 3:55 or lower gears. If I go on a road trip I can swap the 2.76 unit back in. May just go 3.23. My goal is to have a streetable motor and make good power and run pump gas.

    Any ideas or suggestions???? I may just build a stroker with this but right now trying to see what I can get without doing that. Ive seen a few builds on here and the one with low compression etc... was really impressive. Thanks for any tips and suggestions!!!
     
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    • YY1

      YY1 Well-Known Member

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      Better do some good hard lookin' for pistons.

      That's usually the Achilles's heel of 400 builds.

      I've read that a .040 over 440 piston fits, but can't seem to find what the compression height will be.
       
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      • Bronson77

        Bronson77 Active Member

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        I thought Keith Black made pistons for a 400 maybe they are just stroker pistons???? Not sure on that. Don’t need nothing radical on compression but would like more than stock. Keep it where I can run pump gas.
         
      • 33IMP

        33IMP Well-Known Member

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        I would start with a KB 240. (Hypereutectic i believe). High 8s to low 10s compression ratio, depending on heads and gaskets used. Get the compression figured out, and everything else is ordinary big block mopar techniques.
        IQ52s low compression builds are awesome, but he is an awesome engine builder. Mine would not run that well.
        As for the 440 pistons, you would need to find some with very thick piston heads, cause you would have cut at least .100 off the top of the piston.
        KB240 compression height, 1.91, typical 440 ch is 2.02-2.06.
        To the best of my knowledge, the only forged pistons available for a 400 block are stroker pistons.
         
        Last edited: May 5, 2021
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        • PRH

          PRH Well-Known Member

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          The main thing you’re going to give up by not using a longer stroke crank is....... torque.
          Which is a big player when it comes to driving satisfaction in heavy cars with tall gearing.
           
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          • RustyRatRod

            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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            Look at some of Jim Laroy's (IQ52) low compression builds. If this is a street car, low compression is your friend. Your buddy. You don't want to be idling in summer traffic gettin heat soak with 9.5:1 or more.....or maybe you do, I don't know. See if you can find a copy of the April 1998 issue of Mopar Muscle. That's the issue where DLI outlined a stout stock stroke 400 build. They did use a piston that's not made anymore, but you can build that same engine as a low compression build. The general rule of thumb all else being equal, is 3% increase in power for every 1 (ONE) compression point. Read that again and soak it in. Is that really WORTH custom or high cost pistons? Is it WORTH having heat soak and detonation issues in the middle of summer? While you're out trying to have a good time? Trust me, I know. I just got done tuning detonation out of my high compression slant six build. If I could have done it differently, I would have.....AND if it gives me much more problem into the summer......I'll change the milled head out for one not milled "so much".....but I believe I've got it worked out now. Serach "Bare Bones 400" on this site. It shows how I built mine. It's gonna be a stump puller. I can just about guarantee it's gonna have 1 LB FT per cubic inch. That's power you can feel and with less than 8:1 compression and it'll run on 87 all day long.
             
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            • RustyRatRod

              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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              IMO that's a tradeoff. One that can be more fun on the street with the shorter stroke, because it can get to that torque quicker. Like a big block 340.
               
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              • YY1

                YY1 Well-Known Member

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                ..but the main thing you're going to gain with a severely "oversquare" bore size is...torque?
                 
              • RustyRatRod

                RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                Crapped if I know. lol It becomes similar to how the 340s ran, but more exaggerated, since the bore size is so much bigger. Look at Pontiac motors, for example. Small bores and long strokes. Truck motors. Always in a Mopar's rear view mirror, too. I don't know stuff on a physics level, but I know the more surface area a piston has in terms of bore size, the more power can be made. The 400 has a LOT of real estate in terms of piston surface area. Think how good that is for air flow. Even with the short stroke, set up right, a stock stroke 400 can scream......same with a 383. 4.250 ain't no small bore size either.
                 
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                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                  What I was saying was that the short stroke will GET to its torque peak quicker. Think about it. A 3.375 stroke VS a 3.750 stroke. Look at that difference. They each have their advantages. "Just because" the 3.750 is "more" doesn't mean it's "better" for every type of build. That's my opinion and I'm stickin to it. Cause it's right. LOL
                   
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                  • IQ52

                    IQ52 Well-Known Member

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                    • rumblefish360

                      rumblefish360 Getting closer FABO Gold Member

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                      CID. BORE. STROKE
                      340 - 4.04 - 3.31
                      400 - 4.342 - 3.38 (also seen 3.375)

                      .007 stroke increase for the B engine.
                      .302 Piston diameter increase for the 400
                      Looks like it’s a BIG BORE small block.

                      Correct me if I’m wrong ...
                      Stock piston height is 1.812
                      The KB 240’s have a 1.908 height vs a stock 440 of (if I’m correct...) 2.061. = .153 taller for the 440 slug.

                      Now how far down the hole are the stock pistons?
                       
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                      • 80fbody

                        80fbody Well-Known Member

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                        Bet they're way, way down. The last one I measured was like .180 or something.
                         
                      • 33IMP

                        33IMP Well-Known Member

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                        If your figure for the stock slugs compression height is right, (i am NOT questioning you, sir), my calculations show them .122 in the hole, assuming g blueprint specs.
                        So, what is that, 7 1/4 to one?
                         
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                        • YY1

                          YY1 Well-Known Member

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                          Now we're gettin' somewherz.
                           
                        • 33IMP

                          33IMP Well-Known Member

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                          Ran some numbers thru wallace compression ratio calculator. Assuming..... 90cc heads, .041 head gasket, .122 deck flattops with no reliefs, according to wallace, stock real compression is.....


                          7.13 to 1.


                          Should run on kerosine.
                           
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                          • RustyRatRod

                            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                            Mine sits .115" in the hole.
                             
                          • RustyRatRod

                            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                            Yup and you know what? You can make that RUN with a good tune SPECIFICALLY for THAT compression and engine. ....and never have to worry about detonation.
                             
                          • Bronson77

                            Bronson77 Active Member

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                            The Keith Black 240 pistons should bring compression up some correct? And I may run Stealth aluminum heads if that matters. The heads I have are 902 castings. So I think the Stealths would be a upgrade??? And with this combo I should be able to still run pump gas correct? Sorry for the questions just trying to figure out what I could build with this.
                             
                          • Bronson77

                            Bronson77 Active Member

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                            Looks like though it will run good with the low compression though. I’m rebuilding the motor so it will be getting new pistons
                             
                          • 33IMP

                            33IMP Well-Known Member

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                            Icon will give estimates of compression ratio on their website. Im guessing your 902 would have around 90cc. Icon says thats 8.9 with kb240. I dont know what the cc is on steaths, but if its 75cc, icon says a shade over 10 to1. That might be real iffy on pump 91.
                            But then, there are a whole lot of other factors than can make or break a pump gas combo.
                            I do agree with RRR, you might want to build it with stock replacement cast pistons, use the stealth, try for 8 1/4-8 1/2, and build a mild combo for 87, to push that c-body around.
                             
                          • Bronson77

                            Bronson77 Active Member

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                            Yes it’s a heavy car! I plan on a converter upgrade and also putting lower gears in it..... if I were to run at that strip etc..... if I wanna run on the highway I can always swap back. I thought I read somewhere the Stealths were supposed to be around 80cc? Don’t know on that. Maybe stock pistons are the way to go.
                             
                          • mygasser

                            mygasser FABO Gold Member FABO Gold Member

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                            if you're planning to splash out on the stealth heads now and are considering a stroker later i'd do it the other way around. build the stroker for similar money to the heads and a basic build then if you need more later add the heads and you won't have to pull the motor to do it. fit it once and be done with that part. i'm betting the extra torque the stroker gives and you won't need (you may want but that's different) the head swap later. just my 2 cents, but i hate doing stuff twice (rebuild, then rebuild again with a stroker kit).
                            neil.
                             
                          • rumblefish360

                            rumblefish360 Getting closer FABO Gold Member

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                            I don’t know where anything sits on a big block.
                            Im not familiar with them.

                            Stock slugs? IDK myself. But with the 440 slugs, you can move them upwards .153. If the OE 400 slugs are .180 in the hole..... then your .027 in the hole.
                            The piston spec look up was at summit for the replacement slugs for the 400 & 440. If the stock OE 400 is .122 in the hole, then the 440 slug goes up .153 putting the piston above deck more than a good bit.
                            I was thinking Yak piss myself.
                             
                          • 33IMP

                            33IMP Well-Known Member

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                            Yak piss? Thats california pump, isnt it?!?
                            As for the 440 pistons in a 400. Machining a bit off the top of a forged 440 piston, might be the only way to get a forged piston in a stock stroke 400, short of a $1000 set of custom pistons.
                             
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