Home Forums Tech Talk Squish Gap

This topic contains 6 replies, has 6 voices, and was last updated by  Gordon Duax 9 months, 2 weeks ago.

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  • #89697

    Tony Di Benedetto
    Participant

    Will altering the squish gap change RPM ?   Running a ROK and currently maxing out at 14,573rpm.   If I drop base gasket of cylinder will increasing compression boost rpm to 15K+ ?

  • #89712

    Mike Burrill
    Participant

    Tony really good question.  Do you know what your squish gap is currently?  If you close it up too tight you run the risk of the piston contacting it.  I think there are a lot more variables then squish to effect RPM.  Are you racing on tracks with long straights or short?  How long are you at wide open throttle with the maximum RPM reached?

     

    Mike Burrill -
    Karting Kartel

  • #89713

    tony zambos
    Participant

    Agree with Mike. Also, by changing the base gasket, you’re changing the port timing.

    LAD Specialties customer / tony kart / rotax / kt100

  • #89714

    Christian Fox
    Participant

    Mike and Tony are correct, and to Tony’s point, a thinner gasket/tighter squish will lower your exhaust port and retard timing a bit. Yes, you will get more compression, but with a lower exhaust port, you will be moving the engine’s peak hp to a lower rpm band. So, if anything, tightening the squish in the absence of any other adjustment will give you more bottom and mid and hurt your top end. You should be targeting 15k in a Rok, so you aren’t far off. Just add a tooth on the rear.

  • #89757

    Tony Di Benedetto
    Participant

    So, on short tracks with more corners the way to go is dropping size of cylinder base gasket thickness to shift power band down and vice versa for long / fast tracks.   Correct ?

  • #89923

    Walt Gifford
    Participant

    I seriously doubt you will see any performance difference you can feel or measure by changing the thickness of the base gasket. I would not consider it a tuning tool.

    The head clearance is where you will see an increase. If it’s optimized to the minimum without hitting and, centered on the bore, it will burn more efficiently and that counts for allot.

    Increases in compression ratio (to a point) will benefit the lower rpm band but the increase in compression ratio from a gasket change is minuscule.

    Gif

    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

  • #90834

    Gordon Duax
    Participant

    Will altering the squish gap change RPM ? 

    It’s actually the other way around…

    Altering your rpm will change the squish.
    I’ve had a 125 bike engine that was set up with .016″ squish, but if revved above 16k, would go to zero, due to crank flex.

    Would start making a ringing sound above 16k, and when torn down both the piston & head would show light contact.
    It never hurt anything, but I didn’t dare let it rev past that point.
    I just used it as a shift indicator :)

    I am sure this is happening on most engines to some extent.

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