Quench and Squish

Engine, Trans & Driveline

  1. Garys1969RR

    Garys1969RR Well-Known Member

    Messages:
    2,508
    Likes Received:
    743
    Joined:
    Apr 12, 2012
    Location:
    Colorado
    Local Time:
    8:45 AM
    Since there has been a lot of talk lately on this topic of quench, thought I would share what (I think) I know about it. As I understand the thinking on the squish: In an engine that has the flat part of the piston nearly hitting the flat part of the cyl head at TDC, with say .035" clearance to spare, the mixture furthest from the spark plug is shot across the chamber at high speed towards the spark plug. This swirl/turbulence action causes the entire charge to burn more completely and evenly. Especially the portion furthest from the plug. Since the flame front has started traveling across the chamber at say 36 degrees before TDC, this turbulence is shot into the flame front causing a more complete and rapid burn. Then the end charge also has the heat "Quenched" out of it as it nears the end of the chamber, hopefully preventing pre ignitiom. That is where a rogue flame front can ignite from, and travels towards the other flame front. When they collide, then that is where the Ping or knock happens.

    - - - Updated - - -

    All theory and speculation aside, the many motors I have built seem to be more responsive and produce more power with a tight quench distance.
     
    • Like Like x 1
    • Cranky

      Cranky Banned Staff Member FBBO Gold Member

      Messages:
      19,918
      Likes Received:
      16011
      Joined:
      Dec 4, 2009
      Location:
      Pasa-getdown-dena Texas
      Local Time:
      9:45 AM
      Thought I had a thread started here on quench.....but anyways....

      What is the most, exact precisely defined occurrence in all piston engines? It isn’t ignition timing, combustion, crank indexing, or valve events. It is Top Dead Center. You can’t build an engine with an error at Top Dead Center because TDC is what everything else is measured from. Spark scatter, crank flex and cam timing can move, but TDC is when the piston is closest to the cylinder head in any one cylinder. The combustion process gets serious at Top Dead Center and about 12 degrees after TDC, most engines want to have maximum cylinder pressure. If maximum cylinder pressure occurs 10 degrees earlier or later, power goes away. Normal ignition timing is adjusted to achieve max cylinder pressure at 12 degrees after TDC. If your timing was set at 36 degrees before TDC that is a 48 degree head start on our 12 degree ATDC target. A lot of things can happen in 48 degrees and since different cylinders burn at different rates and don’t even burn at the same rate cycle to cycle, each cylinder would likely benefit from custom timing for each cylinder and each cycle. Special tailored timing is possible but there is an easier way—“Magnificent Quench”. Take a coffee can ½ full of gasoline burning with slow flicking flame. Strike the can with a baseball bat and you have what I would call a “fast burn”, much like what we want in the combustion chamber. The fast burn idea helps our performance engine by shortening the overall burn time and the amount of spark lead (negative torque) dialed in with the distributor. If you go from 36 degrees total to 32 degrees total and power increases, you either shortened the burn time or just had too much timing dialed-in in the first place. If you have really shortened the burn time, you won’t need so much burning going on before Top Dead Center. Now you can retard timing and increase HP. Did you ever have an engine that didn’t seem to care what timing it had? This is not the usual case with a fast burn combustion but an old style engine with big differences in optimum timing cylinder to cylinder will need 40 degrees of timing on some and others only need 26 degrees. If you set the distributor at 34 degrees, it is likely that 4 cylinders will want more timing and 4 cylinders will want less ( V-8). Moving the timing just changes, which cylinders are doing most of the work. Go too far and some cylinders may take a vacation. Now what does quench really do? First, it kicks the burning flame front across and around the cylinder at exactly TDC in all cylinders. Even with spark scatter, the big fire happens as the tight quench blasts the 32 degree old flame around the chamber. Just as with the coffee can, big flame or small flame, hit it with a baseball bat and they are all big instantly. The need for custom cylinder-to-cylinder timing gets minimized with a good quench. The more air activity in a cylinder you have the less ignition timing you are likely to need. When you add extra head gaskets to lower compression you usually lose enough quench that it is like striking the burning coffee can with a pencil. No fire ball here and that .070-.090 quench distance acts like a shock absorber for flame travel by slowing down any naturally occurring chamber activity. A slow burn means you need more timing and you will have more burn variation cycle-to-cycle and cylinder-to-cylinder, result more ping. Our step and step dish pistons are designed not only to maximize quench but to allow the flame to travel to the opposite side of the cylinder at TDC. The further the flame is driven, the faster the burn rate and the less timing is required. The step design also reduces the piston surface area and helps the piston top stay below 600 degree f (necessary to keep out of detonation). All of our forged pistons that are lower compression than a flat-top are step or step dish design. A nice thing about the step design is that it allows us to make a lighter piston. Our hypereutectic AMC, Buick, Chrysler, Ford, Oldsmobile and Pontiac all offer step designs. We cannot design a 302 Chevy step dish piston at 12:1 compression ratio but a lot of engines can use it to generate good pump gas compression ratio. Supercharging with a quench has always been difficult. A step dish is generally friendly to supercharging because you can have increased dish volume while maintaining a quench and cool top land temperatures. You may want to read our new design article for more information. ".

      By John Erb
      Chief Engineer
      KB Performance Pistons

      Permission granted to post this article given by Marko Glush of United Engine & Machine - Icon - KB Performance - Silvolite - KB VTwin. mglush@uempistons.com

      And I found it with comments made.... http://www.forbbodiesonly.com/mopar...1-Quench-explained&highlight=Quench+explained
       
      • Like Like x 2
      • Garys1969RR

        Garys1969RR Well-Known Member

        Messages:
        2,508
        Likes Received:
        743
        Joined:
        Apr 12, 2012
        Location:
        Colorado
        Local Time:
        8:45 AM
        Very interesting, I may try using less ignition advance to see if that improves E.T. Will try going From 38 to 36 or 34 total advance. Yes Cranky I'm sure you had started one. Always an interesting subject.
         
      • Banzaiii67

        Banzaiii67 Well-Known Member

        Messages:
        374
        Likes Received:
        156
        Joined:
        Sep 24, 2013
        Location:
        Milwaukie, Oregon
        Local Time:
        7:45 AM
        The top bit is good information..

        However, KB is lying! Why the hell did KB develop pistons with less than stock compression height with valve reliefs? John Erb need to be kicked in the <insert expletive>
         
      • charger318

        charger318 Well-Known Member

        Messages:
        134
        Likes Received:
        13
        Joined:
        Nov 4, 2013
        Location:
        illinois
        Local Time:
        9:45 AM
        I am in the process of learning about quench now looking into a 318 the 273 closed chamber head, and using kb399 dome pistons nit deck block to keep the piston. 010 in the whole plus a .027 head gasket to achieve a .037 quench piston top to heart side of chamber if I am poking at this right????:)
         
      • Garys1969RR

        Garys1969RR Well-Known Member

        Messages:
        2,508
        Likes Received:
        743
        Joined:
        Apr 12, 2012
        Location:
        Colorado
        Local Time:
        8:45 AM
        Not sure what you mean here. Is it the fact that a lower compression height piston wouldn't need valve reliefs? Since the piston is already lower in the bore? I believe they have some for the 440 that are the same C/H as the 440 6 pak piston. That is about .017" down from the deck.
         
      • lewtot184

        lewtot184 Well-Known Member

        Messages:
        4,637
        Likes Received:
        2920
        Joined:
        Aug 21, 2011
        Location:
        indianapolis
        Local Time:
        10:45 AM
        i don't understand the KB is lying thing, but i respect john erb's writings. as far as the 440's and KB go their pistons do use factory compression heigths but add quench domes on a couple of them. i think a lot of confusion and false information surround the quench dome pistons and their use.
         
      • Banzaiii67

        Banzaiii67 Well-Known Member

        Messages:
        374
        Likes Received:
        156
        Joined:
        Sep 24, 2013
        Location:
        Milwaukie, Oregon
        Local Time:
        7:45 AM
        My rant is directed at the KB pistons for the 383. Stock compression height is 1.935, both their offerings are 1.908. I guess i'm in the minority. The statement above is all fine and good, but all of this is assuming your quench within tolerance. Fortunately, I have steel shim head gaskets on my side.

         
      • Cranky

        Cranky Banned Staff Member FBBO Gold Member

        Messages:
        19,918
        Likes Received:
        16011
        Joined:
        Dec 4, 2009
        Location:
        Pasa-getdown-dena Texas
        Local Time:
        9:45 AM
        Isn't compression height measured on the side of the piston where there is no dome? If the reverse dome piston gives say .035 quench and yet yields high compression even with valve reliefs with a lower CH, why would it matter if it's less than the factory CH? After all, the factory piston doesn't have a dome on the quench side of the piston, right?
         
      • lewtot184

        lewtot184 Well-Known Member

        Messages:
        4,637
        Likes Received:
        2920
        Joined:
        Aug 21, 2011
        Location:
        indianapolis
        Local Time:
        10:45 AM
        i think the 1.908 CH is a '67 or earlier CH. the 1.93 is '68 or later. shelf pistons for 383's can be difficult. worst part is no quench domes for 88cc heads.
         
      • Meep-Meep

        Meep-Meep дворянин

        Messages:
        9,874
        Likes Received:
        3633
        Joined:
        Aug 4, 2008
        Location:
        The Missile Base
        Local Time:
        9:45 AM
        I'll make the point, including reinforcing the point in Erb's write up, that basically says less timing will be required in a fast burning chamber. That might be a good way to know for sure if the quench you built into an engine is actually doing a lot of good. Bore size is a big factor regarding burn rates. For example the little Mazda Miatas only require about 20 deg of advance to get the job done and they do not have squat for a quench pad. They are 4 valve pentroof chambers.
         
      • sleepar

        sleepar Well-Known Member

        Messages:
        1,509
        Likes Received:
        293
        Joined:
        Nov 20, 2013
        Location:
        Ft Lauderdale fla.
        Local Time:
        10:45 AM
        My 8/66 LA318 has the shim type gaskets on the heads and intake.... if I use the regular ones am I killing what little quench the factory gave me... or does it only matter over a certain amount of compression?
         
      • Meep-Meep

        Meep-Meep дворянин

        Messages:
        9,874
        Likes Received:
        3633
        Joined:
        Aug 4, 2008
        Location:
        The Missile Base
        Local Time:
        9:45 AM
        Quench is always good but you might have to look pretty hard to find a noticeable difference between the shim gasket or the comp one.
         
      • Challenger340

        Challenger340 Well-Known Member

        Messages:
        408
        Likes Received:
        379
        Joined:
        Mar 4, 2014
        Location:
        jaffray, B.C. Canada
        Local Time:
        8:45 AM
        Aside from the obvious connotations to the word "Quench" being to assist in purging the wedge chamber ?
        and,
        the considered relevant/accepted distances on the internet for adequate quench on a wedge chamber, and less than .050" as optimal ?
        Keep in mind here that there is FAR MORE going on than just "quench" by itself and the role it plays in exhaust scavenging.
        To wit;
        actual "quench" distance, is relative to the area being quenched, both in terms of a percentage of total Bore area, and EXHAUST Port efficiency.
        for example;
        Sometimes.... .040" quench can KILL power on the Dyno on a 4.375" Bore on a particular wedge head, versus even .070" ?? seen it many times on the Dyno... OVER SCAVENGING !
        Just saying.... IMO
        don't get your pants in a knot all worried about quench ?
        Try for .050" or slightly less as a decent "rule of thumb" for DIY guys on wedges, on any Bore Size, and you won't be too far off. But attempting any type of magic gains past that with quench... just ain't there without one heck of alot of Flow data, and Camshaft simulations.

        Look at HEMI's ??
        where is the "quench" there ?? and they can easily run far more Compression than a wedge with NO DETONATION !
         
      1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
        By continuing to use this site, you are consenting to our use of cookies.