Stroker Build... maybe

Small Block Mopar Engine

  1. MPH426

    MPH426 Active Member

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    A while back... my engine indulged itself in a slight smathering of steel dust. The rocker arm setup was ball and cup. One of the rocker arm balls broke off. The wasn't much dust (.003 .005) that I found, but it was everywhere. Since this happened, I really don't trust the spinning assembly.
    The bare block is being hot tanked. While this is happening, I'm thinking about putting a stroker kit in. The existing pieces parts might be okay, but as long as it's torn down. I might as well look into it. Realize that it's been 35 years since I've owned a hot rod. Back in the day, my nick name was Dirty Mike 'cause I was always working on cars. Pretty much all big blocks. Including the big block 318. :) From what I remember 1966 was the last year for it.
    That said, I have a few questions regarding the 340 that I have not been able to find the info I'm interested in.
    1: How large can the bore be on a 340 without risking issues? My recollection was .060 (for the 440 anyway.. I could be wrong)
    2: How long of a stroke can I get away with, without having to do to much metal removal for clearance of the spinning assembly?

    The jist of this is, I'd like to end up with a 426CID small block. :D
    With a 4.12" bore and a 4" stroke or a 4.07 bore (what it is now) and a 4.1 stroke, either would yield the desired displacement. I have found cranks with both 4 and 4.1 stroke.
    The formula that I used is this: "echo "scale=3 ; (3.14 * 2.060 * 2.060 * 4)*8" | bc -l" This was done on a Linux box where bc is a basic calculator. I adjusted the bore and stroke as necessary.

    If it can't be done safely, not a big deal. :D
    Thanks!
     
    Last edited: Sep 29, 2021
  2. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    1; A sonic check will tell you how far you can go. I had 1 - 340 @.020 that was left with a cylinder wall thickness of .037 & less in thickness in some spots.

    2; How much of the bottom of the cylinder that needs to be ground for clearance can depend on the connecting rod used.

    The biggest stroke small block crank I have seen was a massive 4.25.
     
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    • Garrett Ellison

      Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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      I have found Bore X Bore X .7854 (1/4 Pi) X Stroke X # of cylinders works very well.
       
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      • rumblefish360

        rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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        I gave up the pen pad and just use a on line calculator
         
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        • S'cuder

          S'cuder FABO Gold Member FABO Gold Member

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          Volume of a cylinder is pi r squared h, where pi is 3.14, r is 1/2 bore, and h is stroke. Then multiply by the number of cylinders.
           
        • 70dart340

          70dart340 FABO Gold Member FABO Gold Member

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          3.1415926, if you want to be super accurate....
           
        • brian6pac

          brian6pac Well-Known Member

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          FYI, found this about Pi on the internet, Some people have more time on there hands than I do.

          How many digits has pi been calculated to? The value of the number pi has been calculated to a new world record length of 31 trillion digits, far past the previous record of 22 trillion. With that being said, what is the 31 trillionth digit of pi? Google announced the milestone on Thursday March 14, also known as Pi Day (3.14).
           
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          • S'cuder

            S'cuder FABO Gold Member FABO Gold Member

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            Look up the rule for multiplying significant digits. Many of those digits are meaningless.
             
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            • 70dart340

              70dart340 FABO Gold Member FABO Gold Member

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              I know, but it's a plug for my youngest son. After 2 degrees in June from the U Dub(University of Washington), he's starting his full scholarship for his PhD in Astrophysics at Vanderbilt in Nashville. This kid is costing me a fortune, but my wife and I will pay every dime for his education. He has difficulty changing his oil, but blows us away in math and astronomy. My bad.
               
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              • flyfish

                flyfish C8H18+N2O = :-D

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                I would leave as much meat in the block as you can. A friend of mine made a "426" small block (magnum), but I forget where he got the crank. Also, be sure to leave money in the budget to replace those cheap rockers with some quality rockers (Comp pro mags are the ones I use).
                 
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                • D-mailman

                  D-mailman Well-Known Member

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                  Bore X Bore X Stroke X 6.2832 , This for 8 cylinders . Works for me .
                   
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                  • 33IMP

                    33IMP Well-Known Member

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                    If you have to have a 426, i would much prefer the 4.07x4.10 combo. Keep the cylinder walls as thick as possible!
                    I have an acquaintance that ran some BIG small blocks. His 481 ran hard, but his 502 small block didnt last.
                    He's on his second new demon now.
                     
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                    • pittsburghracer

                      pittsburghracer FABO Gold Member FABO Gold Member

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                      Sometimes I read a post and just shake my head. You want to end up with exactly a 426 engine to impress your friends or yourself learn to lie. Hell ya I know it’s a 424 but my friends aren’t smart enough to figure it out.
                       
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                      • furrystump

                        furrystump Well-Known Member

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                        You can just run a smaller rod end. Chevy or even honda size. I would go to Molnar Industries or K1 or Ohio crankshaft. See what kits would fit the best. I would go more stroke and leave the walls as thick as possible. Then when you have 422 or 434 or 444 just say its 426. I tell people my 410 is a 340.
                         
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                        • brian6pac

                          brian6pac Well-Known Member

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                          I have always used 3.1416
                           
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                          • 33IMP

                            33IMP Well-Known Member

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                            When people ask how big my big block chevy is, i tell em its a hundred over 396.
                            Not my fault if they think 415, instead of 496.
                             
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                            • Heywodja

                              Heywodja The Heartbeat Stops Here FABO Gold Member

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                              8D1B35E6-37C5-42E5-85E2-2DECFDD59664.jpeg
                               
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                              • MPH426

                                MPH426 Active Member

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                                Thanks for all the replies. Apparently there's a lot of people who like calculating the cylinder volume. LOL
                                If I do go this route, it would be with the current 4.07" bore and a 4.1" stroke... I'll probably go with something a bit milder. I want to still be able to run pump gas so I need to keep the compression ratio from getting out of hand. Then again, I may just rebuild it as it was. It ran pretty strong.
                                 
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                                • S'cuder

                                  S'cuder FABO Gold Member FABO Gold Member

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                                  Molnar makes a 4.15" crank with small rod journals for block clearance. You'd need matching rods and probably a custom piston. With your bore, it would give you a hair under 432 cu in.
                                   
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                                  • pittsburghracer

                                    pittsburghracer FABO Gold Member FABO Gold Member

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                                    First thing I would do is make some phone calls to see what is available. This isn’t 2019 anymore and stuff continues to get harder and harder to find in stock. I was going to sell off my 422 rods and crank but have since changed my mind for now till things start coming again.
                                     
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                                    • MPH426

                                      MPH426 Active Member

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                                      @S'cuder & pittsbughracer. Thanks! great suggestions
                                       
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                                      • mopar65

                                        mopar65 Well-Known Member

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