Explain Quench to me.....GO!

Mopar General Discussions

  1. airwoofer

    airwoofer Drivetrain limit explorer

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    [​IMG]

    I have domed pistons in the 540 and like the picture above the dome seems like it would cut the chamber in half and prevent the squished mixture that is coming from the quench area from a straight shot at the spark plug which is on the other side of the hump. Anybody else loose sleep over this?
     
  2. MopaR&D

    MopaR&D Nerd Member

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    This is very real and does affect combustion dynamics. Smaller chamber is the most efficient way to get more compression as that shrouding doesn't happen from the piston dome. One big reason why deep Hemi chambera
     
  3. nothingbutdarts

    nothingbutdarts Well-Known Member

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  4. nm9stheham

    nm9stheham Well-Known Member

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    Just read this, very good write up!

    I will add that in some open chamber engines, there have been quench dome pistons made that create the squish with a shaped, raised dome that pushes high up into one side of the combustion chamber. The top shaping of this dome is identical to that part of the combustion chamber and so the shaped dome top moving up very close to the combustion chamber provides the swirl and quench effect. I had some TRW forged pistons back in the early 70's for a 2 bbl 351C that were designed exactly this way; the dome was a 'mountain' shaped dome on the spark plug side to create the quench area; there was a notch in the 'mountain' for the spark to shoot through.

    Not sure if anyone makes pistons like this anymore but the principle is the same: 'squirt and swirl' the mixture just before combustion. The old Mitsubishi 'MCA Jet' idea achieved the same end but in a very different way for their more open hemi head designs.
     
  5. Marcohotrod

    Marcohotrod Well-Known Member

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    much good info but like nm9s said there is a big piece missing for us mopar folks useing certain factory heads. 1968+ big block, many 318, all 340 and early 360 heads have a fully round open chamber with a recessed area where we want quench. I measured this recess on a 340 head at .090". so a copied chevy small block article that states "quench is nothing more than the piston in the hole depth plus the head gasket thickness" is lacking for many mopar engines. for engines with fully round open chambers quench is the piston in the hole depth plus head gasket thickness plus head recess
     
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    • jerry6

      jerry6 Banned

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      OP , thanks for the explanation .
      The recess in the 340 open chamber Ede heads are .060 , I had them cut now closed chamber , seems to have worked really well . Car runs better ,compression and gas mileage has gone up . Calculated 11.3 , runs great on super 94 , will try it on 91 octane see if it pings .
       
    • nm9stheham

      nm9stheham Well-Known Member

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      BTW, the KB243 pistons have a step up on the piston that can be used to fill that gap to some degree. You will still have to do some decking or head shaving (about the thickness of the head gasket or a bit more) to get it down to a usable quench gap with the open head.
       
    • mech1nxh

      mech1nxh CUSTOM TITLE FABO Gold Member

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      Yes, and No,
      triangular taper on the 'hump', pointed at the plug about .010 total, inclusive :D
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      My 367 runs .034Q/10.7Scr, with KB167s and Eddies. It seems to make full power on 32*,and is quite happy on 87E10.With a 223/230/110 cam, it made phenomenal fuel mileage. It hasn't been opened since 2004, and has over 100,000 miles on it.
      Is it due to the Quench?
      I like to think it pays a significant role.
       
    • Killer6

      Killer6 Well-Known Member

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      First, no hemi is a "hemi", but gens I&II are as close as you'll get
      Second,they and 4V engines don't require the squish or quench to
      combat detonation near as much because of the superior plug pos.
      Third,not all "wedge" heads are created equal,far from it. and BB
      mopars are among the worst.Valve position and angle,and plug pos.
      Fourth,quench and squish are not the same,even though they can
      occupy the same area of a combustion chamber.They have different
      goals,and if you look at open quench style BBM heads,even w/OE
      flat top 10:1 slugs, the gap is .195" w/a .017" shim gasket on a 440.
      The difference is a matter of degree,and anywhere between .130" &
      .050" is a detonation danger zone.Over you have quench,under you
      have squish,the latter being far superior.Squish can be accomplished
      and effective anywhere in the chamber,quench can only be effective
      in the area farthest from the point of ignition.
      Lastly,minimizing/eliminating detonation means power & reliability.
       
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      • Wyrmrider

        Wyrmrider Well-Known Member

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        I clicked agree
        actually squish helps on the early Hemis and 4v OHC motors
        on the early hemi we got it by using a larger bore against the early head (which has raised ports in any case compared to the 392
        you can do the same thing with the late hemi
        you can also run the dome next to the combustion chamber on the side away from the plug
        if running big valves you have to radius the top of the block where the intake is flow does not like to hit sharp top of block and neither does the valve
        and BBM is about the worst post 1967 915 head
        even there the plug and valve location is about as bad as you can get
        the 361-413 Truck motor used spark plugs in the 1958 Ford FE locations (same locations later used by the LA engine) so Chrysler did understand the problem- and makes them much easier to change (still not so good chamber but about same as most at
        BBM introduction in 58)
        so why not in the BBM?
        our loss

        oops did not notice date on this thread- still good
         
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        • mbaird

          mbaird mbaird FABO Gold Member

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          Good info is never too late !

          So 361/413 truck heads would work well for a torque motor ? Were they closed chambered ?
           
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          • famous bob

            famous bob mopar misfit FABO Gold Member

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            I don't agree with a few statements about hemi`s in these posts --------------nuff said
             
          • Wyrmrider

            Wyrmrider Well-Known Member

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            361-413 truck motors heads are big and heavy and use longer valves
            exhausts are 1.5ish and sodium cooled with 7/16 stems
            yes basically early B/RB closed chamber
            we built a set for a roadster one time
            looked let's say unique
            history
            early 60's Winternationals in Pomona Micky Thompson had a menagerie of Pontiacs
            2 cyl, 4 cyl cut apart V8s
            Tempests which were usually transaxles with conventional RWD
            one of his V8's had Ford/ LA angled sparkplugs and separate exhausts
            They covered it up and no photos- never seen any or read anything on this motor
            This was before his Hemi's
            BTW this Hemi was cored so it could be drilled for most any 4 bolt block
            Produced for Ford and Pontiac and I think Chrysler
            He won top eliminator with the Pontiac version
            could have been made for Cad, Olds, others
            Wonder what happened to the tooling?
            Come on Bob- disagree- I had lots of Ideas- mostly bad
             
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            • MopaR&D

              MopaR&D Nerd Member

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              I'm glad to see this thread going again... since the last time I posted a few years ago (f.k.a. "MOPEkidD-3") the 360 I had in my Duster went kaput and I put together another one which I got running this past April. My previous 360 was an LA block with stock iron Magnum heads, bored .060" with KB flat-tops and pretty close to zero deck (maybe .005" below). Quench height was around .042-.045". Compression was 10.5:1 and I was using a mild Lunati Voodoo HFT cam which made the cylinder pressure way too high (short-duration high-lift intended for smaller low-comp engines) and caused repeated pinging which is what eventually killed it. Anyway I have noticed pretty big differences in the way these two engines run because my "new" one is an all-stock 5.9L Magnum short block with heavily ported Edelbrock RPM "open" (milled) chamber heads, the ones meant for old high-comp 340s with pop-up pistons. With the milled chambers being .050" deep, stock Magnum pistons .050" down in the hole and .027" Cometic gaskets I'm right at the upper edge of the "detonation danger zone" as mentioned in post #35 but considering the compression ratio is only 9:1 and I have a proper custom-ground cam with sufficient duration for the combo I have yet to encounter any pinging even running regular gas (85-octane here at high altitude) and almost 40* total timing (initial + mech).

              Here's where the comparison gets interesting. As you can imagine my old 360 was a torque monster and had incredible throttle response; you stepped on the go pedal at any RPM and it just picked the car up and moved. My new one doesn't have quite the same level of responsiveness and torque especially below 3000 RPM or so but because of the ported heads and bigger cam the overall HP is much higher and the powerband is much wider (current one pulls hard to 6000+ RPM, old one ran out of breath by 5000 RPM). Now we get into the squish vs. no-squish discussion; since I used the same 750 cfm Street Demon as my old 360 it became obvious during tuning this new engine wants a LOT more fuel. Like there's noticeably less power especially in the higher revs if the AFR on my wideband O2 gauge is leaner than about 12.5:1; my old 360 made max power with 13-13.5:1. Also with my old 360 I was able to lean out the part-throttle cruising circuit all the way to 16:1 or leaner and it would still have good response and run smooth when easing into the throttle (like going up a hill) without making extra heat. This new 360 really doesn't like to run much leaner than 15:1 at any time and even at that AFR I noticed it ran a bit hot at freeway speeds (~3000 RPM) so I put it back to 14-14.5:1 at cruise. As you can imagine gas mileage is also much lower; around town my old 360 got 14-15 MPG, current one gets about 11. But then again I had to always run premium with the old engine, the new one drinks cheapo regular just fine.

              I think what I've learned from this is the whole tight quench deal has the most benefits at part-throttle. If you're building an engine and your only goal is WOT power then the squish thing is not really worth your time unless it's for competition where rules limit what you can do and you need to squeeze every last bit of HP you can get. But if you are building an engine that will see lots of street miles (or something like a circle track engine) and decent gas mileage is a goal then building for squish is totally worth it IMO.
               
            • mbaird

              mbaird mbaird FABO Gold Member

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              I have a near identical 5.9 build right now and am finding it too wants a ton of fuel ! So much that my bumper has fuel on it. Yet the plugs are tan.

              As for the 413 heads... they might be a great way to build a motorhome engine with a little higher compression. Weight would not make a difference in that application.
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              Your plugs SHOULD be a dull white on the porcelain all the way down to the fuel ring in the bottom of the shell.

              If your plugs are tan it is rich.
               
            • mbaird

              mbaird mbaird FABO Gold Member

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              I understood white to be lean. Tan to be normal and black rich ...
              It is said that todays fuel makes it harder to read plugs.
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              None of which is true. I've got a meeting at noon and when I get home I'll post some pictures of my sorry tune up and let you see what a somewhat close tune up looks like.
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              image.jpeg Here is an ok tune. I'm still working on it.

              You can see the fuel ring at the bottom. It's way too wide.

              I'm a touch rich at idle. You can see that little bit of white at the top, where is should be all white.

              The area between the fuel ring at the bottom and what should be a clean white tip is cruise, and as you can see, I'm rich there too.

              So I need to get the idle cleaned up first, then work out my cruise issues before I finally get WOT corrected. I'm converting to 1:1 linkage so I need to work both primary and secondary sides together.
               
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