Buying one of these this payday

Discussion in '2-Stroke Engines' started by Randall, Sep 24, 2016.

  1. Randall

    Randall Member


  2. Steve Best

    Steve Best Active Member

    Site is down
     
  3. zippinaround

    zippinaround Active Member

    [​IMG]
    Mid-Level Includes:
    66cc Race-Ready GT5 Engine
    Billet Aluminum High-Compression Head (6cc combustion chamber)
    Port-Matched Billet Straight-Shot Intake Manifold
    Ported cylinder for advanced timing
    Piston ramped at the exhaust & skirt trimmed at intake.
    NGK High-Performance Spark Plug
    NGK Water-Proof Spark Plug Boot
    12+” of 7mm copper-core wire
    1 Racing Carburetor (with 6 total jets)
    1 longer-pull throttle cable
    Studs in cylinder replaced with grade 8.8 studs & hardware.
    This is the engine only, no kit included. Please select KIT UPGRADE for the full kit.
    Select KIT UPGRADE. Includes: Throttle, Exhaust, Mounting hardware, #415 Heavy Duty Chain...

    $309.99
     
  4. Neptunati

    Neptunati New Member

    Get a GT80 Bro. Much better engine imo. Plus the reeds give you gobs of low end torque.
     
  5. jaguar

    jaguar Well-Known Member

    they should pay you for taking that monstrosity off their hands.
    The head should have 7.5cc, not 6cc. Compression will be too high causing the cylinder plating to flake off. And it will wear out the bearings. When you make a big increase in compression you have to retard the ignition which prevents excessive combustion pressure.

    People are duped so easy.
    P.T.Barnum said "there's a sucker born every minute".

    Most of the MB aftermarket industry is based on the ability to sucker people. If I said this on the other forum I'd get kicked off. At least I can tell the truth here but I find I'm a lone voice crying in the wilderness.
     
    BikeBuilder43 likes this.
  6. Demo_Ricky-Bobby

    Demo_Ricky-Bobby New Member

    No i pretty mich agree with u
    Alot of people get suckered in to buying sh!t they dont need and most of the time its all beauty and no proformance
     
  7. jaguar

    jaguar Well-Known Member

    Having a squish band is a selling point but it's near impossible to design the head to only give 130psi while there is a squish band taking up space. According to Jennings they aren't needed anyway for engines that rev less than 9000 or that don't have high compression. And if the buyer doesn't adjust things so that the squish clearance is around .6mm then they actually decrease performance compared to a head with the same psi and no squish band. Since there's always too much space there and since no one goes to the trouble to adjust it then the heads should not be designed with a squish band.
     
  8. FurryOnTheInside

    FurryOnTheInside Active Member

    I sort of agree, except for the point that it is advertised as a race engine and the vendor specifically states that it is not intended for street use. They don't claim it's good for commuting or long distance touring.
    Okay so the chrome will flake off but the cylinders are cheap disposable items, only modified with a bit of porting, and bottom ends are totally stock as far as I can see, just a bit of fancy paint.
    In a race situation, who cares about longevity? It only needs to last until the chequered flag.
     
  9. jaguar

    jaguar Well-Known Member

    I highly doubt that buyers of that engine would agree with you.
    If the seller told the truth of the problems that the high compression head would cause I doubt anyone would buy it.
     
  10. FurryOnTheInside

    FurryOnTheInside Active Member

    I think you credit people with too much intelligence and foresight!
     
  11. jaguar

    jaguar Well-Known Member

    ha-ha! yeah you're probably right.
    People believe hype quicker than they believe scientific evidence.
     
  12. gary55

    gary55 Active Member

    I have been hearing a lot of differing opinions on the so called high compression heads so I tested them myself. 6 cc head on the left, standard kings motors slant plug head on the right. Cylinder decked to 2.720 approx. .020 removed and stock gasket set up. 6cc head reads 125 lbs. stock slant plug head reads 150 lbs.. I would love to hear others results if anyone has tried this themselves so we are not just guessing at the benefits or draw backs these heads provide. I should have done this long ago because it has me re thinking my cylinder work when using slant plug heads.
    [​IMG]
     
    Last edited: Sep 28, 2016
    FurryOnTheInside likes this.
  13. zippinaround

    zippinaround Active Member

    you mean a the stock head was higher compression than the so called high comp head?

    i dont have a compression tester but think i might just get a 300psi guage and some fittings at local hardware store and make one? i have a slant head that has a massive deep chamber and another stock one has a ridge almost flush with the head , the deep one is off a so called 79cc and the other is a so called 60cc.


    but would like to test myself and see what the cranking pressure is.
     
    Last edited: Sep 28, 2016
  14. gary55

    gary55 Active Member

    Sorry I forgot to upload the pics. Yes I was surprised too. Check out the heads I tested. I uploaded them in post # 12
     
  15. Steve Best

    Steve Best Active Member

    Well Jag, i'm a guy who has read and followed Gordon Jennings' bible (2 Stroke Tuner's Guide) since 1976, building pipes and stuffing cases and testing what ever Gord put on paper on sleds, bikes, quads, outboards and gas powered utility tools. I've cut a lot of heads and really changed the nature of a bunch of engines with sometimes nothing more than the change of a squish band and chamber shape. Here is an experiment with same chamber volume and squish area, different chamber shape:
    [​IMG]
    Same compression, completely different power characteristics.
    Head on the left is a mid range torquer. No detonation, strong below the pipe, hard pipe hit and run, then a sharp cut off. No over-rev.
    Head on the right is mild under the pipe, a little more sensitive to timing and screamer once the pipe hits. Revs to the moon..
    Same engine, same pipe, same quench area, same quench gap. Left is toroidal chamber, right is hemispherical.
    Gordon hinted at these things in 1974 but much of this knowledge came out in the 1990s.

    Two further heads cut for comparison:
    [​IMG]
    These were fine tuning the squish band area. We (my son and I) also cut heads looking at various radii and squish band angles.
    Even these China Girl engines I tested different squish band widths from 0.300" to nothing and gaps from 0.100" to 0.010".
    I know what I am talking about. I read the books, know the theories and I tried it. Back to back tested it climbing a hill.

    There are optimums and they definitely make a difference in both high and low rpm.
    This chamber shape below is called "torroidal" and can make your engine into a low rpm (1000-4000) tractor:
    [​IMG]
    Chamber shape is important but the squish is part of how this works.
    This shape actually shuts the engine down at high rpm, preventing run-away rpm.
    Through the 2000s and into the 2010s it was the MX chamber of choice.
    They are now using shallower version to gain more rpm in the past few years, while still keeping the low and mid range torque.

    I bring this up to show that much has been learned since Gordon wrote his ground breaking book in 1974.
    There are a lot of factors involved and while my experience does not agree with Jag's opinion on squish,
    I do agree with Jag that it is a whole lot more complicated than "6cc=power!"
    I am also very grateful for his compendium of knowledge on his website. Truly a good place to start.

    Steve
     
    Last edited: Sep 28, 2016
    FurryOnTheInside likes this.
  16. zippinaround

    zippinaround Active Member

    nice that looks like the deep slant head i have , but the other one i have think the compression is too high might need a second base gasket.

    have you measured them with a syringe? see exactly what cc they really are?
     
  17. zippinaround

    zippinaround Active Member

    so what do you recommend for our china girls ? you have any pics of the ones you experimented with?
     
  18. Steve Best

    Steve Best Active Member

    The one to the right is stock, the one to the front revs to 10,000 with strong power and no detonation.
    It is a modified slant head. Cut a squish band at 2 degrees taper to 0.200" (4-5mm) or so, gap it at 0.035" (slightly under 1mm) or so.
    Most important it goes out to the full 47mm!
    [​IMG]
    The one to the left is an RSE head, starts easy and makes great torque but gives up 5mph. I like it in hills country.

    Steve
     
    zippinaround likes this.
  19. jaguar

    jaguar Well-Known Member

    there is no way a stock slant plug head gives 150psi if no metal was taken off the head or the cylinder. These engines are designed to be low power so they can pass most regulations of countries. That's why they come with low compression. Mine measured at 90psi.
     
  20. Steve Best

    Steve Best Active Member

    Gary explained "Cylinder decked to 2.720 approx. .020 removed"
     
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