Loading ...
Sorry, an error occurred while loading the content.
 

Re: squish clearances

Expand Messages
  • djtcz2001
    ... Some folks would challenge these folks authority, but I don t. Jennings 2 stroke handbook, Jenkins Chevrolet racing engine, Smokey Yunicks Power
    Message 1 of 7 , Aug 1, 2003
      --- In mc-engine@yahoogroups.com, "indo2002nz" <Indo2002nz@y...>
      wrote:
      > Does anyone know where to find an authoritive reference listing
      > recommended squish clearances for different engine capacities,
      > compression ratios and fuel octane ratings.

      Some folks would challenge these folks "authority," but I don't.
      Jennings "2 stroke handbook," Jenkins' "Chevrolet racing engine,"
      Smokey Yunicks "Power secrets."
    • Ken Canaga
      It s hard to find a lot of general purpose info on squish clearances. For a racer the whole point is usually to get the squish as small as possible without
      Message 2 of 7 , Aug 1, 2003
        It's hard to find a lot of general purpose info on squish clearances.  For a racer the whole point is usually to get the squish as small as possible without the piston hitting the head, so it varies a lot depending on the engine design (crank flex, rod stretch, bore size and clearance, etc.).  You can find specific minimums for popular engines pretty easily in the tuning books.  If you're not looking for the max compression ratio, I think Smokey mentioned some tests on Chevy small blocks that showed you retained all the good effects of a squish area (more turbulence, etc.) as long as the squish clearance didn't get any larger than .050 in. 
         
        Ken 
        ----- Original Message -----
        From: djtcz2001
        Sent: Friday, August 01, 2003 1:20 PM
        Subject: Re: squish clearances

        --- In mc-engine@yahoogroups.com, "indo2002nz" <Indo2002nz@y...>
        wrote:
        > Does anyone know where to find an authoritive reference listing
        > recommended squish clearances for different engine capacities,
        > compression ratios and fuel octane ratings.

        Some folks would challenge these folks "authority," but I don't. 
        Jennings "2 stroke handbook," Jenkins' "Chevrolet racing engine,"
        Smokey Yunicks "Power secrets."



        unsubscribe: mailto:mc-engine-unsubscribe@yahoogroups.com

        Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
      • Peter
        I have a copy as well but I dont think Mr. Bell was aware of evrything that would be developed after he left us., maybe he was cos the guy was pretty smart.
        Message 3 of 7 , Aug 2, 2003
          I have a copy as well but I dont think Mr. Bell was aware of
          evrything that would be developed after he left us., maybe he was cos
          the guy was pretty smart. keep reducing squish until either piston
          hits the head or you get pre-ignition! Then you'll know exactly how
          far you can go with that engine, next one (even from same
          manufacturer/year/etc) may be different.
          PJ

          --- In mc-engine@yahoogroups.com, "Tim Sirk" <timsirk@h...> wrote:
          >
          > I have a copy. What do you need?
          >
          >
          >
          >
          > Best Regards,
          >
          > Tim Sirk
          >
          >
          >
          >
          >
          > ----Original Message Follows----
          > From: "indo2002nz" <Indo2002nz@y...>
          > Reply-To: mc-engine@yahoogroups.com
          > To: mc-engine@yahoogroups.com
          > Subject: squish clearances
          > Date: Wed, 30 Jul 2003 13:06:31 -0000
          >
          > Does anyone know where to find an authoritive reference listing
          > recommended squish clearances for different engine capacities,
          > compression ratios and fuel octane ratings.
          >
          > I saw a reference to Graham Bell's Two Stroke book but don't have
          > access to a copy.
          >
          > Thanks and Cheers
          > Johno
          >
          > _________________________________________________________________
          > Protect your PC - get McAfee.com VirusScan Online
          > http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
        • raymanz93@earthlink.net
          ... But PJ, I think, properly done, reducing squish clearance toward the head-kissing stage gets you FARTHER AWAY from the likelihood of combustion
          Message 4 of 7 , Aug 3, 2003
            > keep reducing squish until either piston
            > hits the head or you get pre-ignition!

            But PJ,
            I think, properly done, reducing squish clearance toward the "head-kissing" stage gets you FARTHER AWAY from the likelihood of combustion anomalies, not closer to. By tightening squish, you're not courting disaster, you're avoiding it.

            Wouldn't surprise me to find that tightening the squish clearance (and therefore, raising the C.R. slightly) on an already detonation-challenged chamber would actually ameliorate knocking, not exacerbate it. (can I say that here?)

            I have read that squish clearances over .030-inch begin to lose effectiveness. Also, I don't think the workable squish clearance is in any way related to bore size... as was implied in an earlier message here. From what I've been able to read on the subject, if squish clearance goes much over the .030-to-.040" range (no matter the bore size), combustion starts to become possible in the actual squish band, and that's exactly what we're trying to avoid. So, the tighter the better.

            Of course, the REAL problem with maintaining a a .020" squish clearance on a (for instance) hot-rodded 500+ CID Chevy motor would be that the heavy uppy-downy parts are actually heavy enough to stretch the rods and quickly erase the clearances you thought you had. (and DID have, at lower RPM's)

            When the uppy-downy stuff starts to hold hands, one could easily run over one's own crankshaft.

            jrc in SC
          • David Kath
            FWIW ... Squish clearance of 45 thou on a high reving BSA Gold Star vintage race engine with the obsolete two valve hemi chamber seems to work nicely. No
            Message 5 of 7 , Aug 10, 2003
              FWIW ... Squish clearance of 45 thou on a high reving BSA Gold Star vintage race engine with the obsolete two valve hemi chamber seems to work nicely. No clatter/bang of piston/head interference. 11:1+ compresh on race gas OK. But a nice modern rigid pressed up cro-mo crank and modern rod are being used.

              Speaking of squish ... Something that has always been in back of my mind is what is talked about in books on tuning the small block Chevy race engines. I guess everyone is aware of the offset flattish squish area in the the combustion chamber of these two valve heads. This has long been a performance feature of these engines.
              Anyhow ... It's warned that a squish area of around 100 thou is very dangerous and will actually support/cause detonation vs a thicker or thinner squish. True, a squish of this thickness will cause desirable turbulence in the mix at TDC, but a 100 thou is also a large enough area/thickness to allow the mix in the squish to burn and light off *After* the initial chamber burn begins. This area lights off from the heat of the initial burn and not the original ignition. Natch, when the
              two flame fronts collide you have an explosion of the main mix vs a controlled burn and the "dreaded detonation hammer", tries to ruin your engine. Of course every engine reacts a bit differently ... and I hope I'm not being overly simplistic here for everyone.
              dave - NV
              silly me, still trying to make "old stuff", run well.

              raymanz93@... wrote:

              > > keep reducing squish until either piston
              > > hits the head or you get pre-ignition!
              >
            Your message has been successfully submitted and would be delivered to recipients shortly.