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Thread: PWC Terminology

  1. #11
    Bernies10's Avatar
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    What a machine to start on I remember the first time i rode a pwc, was one of those rental yamaha 700's, I actually stopped at standstill in order to turn, took me like several sessions before i could actually do it properly, thing felt like a rocket back than
    Your SVHO will be much more terrifying, :P But hours of endless fun PS be careful of the mod bug, endless money pit


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    scott2640's Avatar
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    Believe me I will be working very hard to become a proficient operator before I utilize the power of the machine. This was not what I intended to buy but the dealer made me an offer I just couldn't refuse. He was very eager to get rid of the 2014's. I hope I don't regret not having the RIDE system.

  3. #13
    scott2640's Avatar
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    I'm actually in new Smyrna, Florida on vacation and we will be renting a couple of skis Monday. Hopefully I can get a jump start on my skill building.

  4. #14
    Bernies10's Avatar
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    Quote Originally Posted by scott2640 View Post
    Believe me I will be working very hard to become a proficient operator before I utilize the power of the machine. This was not what I intended to buy but the dealer made me an offer I just couldn't refuse. He was very eager to get rid of the 2014's. I hope I don't regret not having the RIDE system.
    All Fz users are in the same situation, RIDE isn't available for us yet, I mean i'm sure it makes life a lot easier but if you've never used it, you won't miss it


  5. #15
    Connecticut CrazyA's Avatar
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    PWC Glossary Of Terms

    Back in the day, there used to be a couple of different sources for huge glossaries of terms. I will try to find them.
    Until I can or can't find them, I will start with this… Propulsion, impeller and jet pump terms. In no way is this list anywhere near complete, but it is something to start with. not all terms and parts will necessarily be related to every single ski, but it's still very helpful.


    Blade tip: The part of the blade nearest the liner or wear ring.
    Blade face: The side of the blade facing the rear of the pump, known as the positive pressure side of the blade.
    Blade back: The side of the blade facing the front of the pump, known as the negative pressure side of the blade.

    Blade root: The point at which the blade attaches to the hub.

    Cavitation: The separation or implosion of air and water and the heat associated. This creates cavities or pockets of air, damaging the impeller, pump and performance of the craft.
    Cup: A radius on the blade face at the outside edge of the blade that controls deflection and accelerates water.
    Diameter: The overall width of the impeller from blade tip to blade tip.
    Driveshaft: The shaft that connects the engine to the jet-pump and transfers torque to the impeller.
    Gullet: The area forward of the impeller known as the intake housing to channel water toward the impeller via vacuum.
    Hub: The center of the impeller that fits over the drive shaft.
    Impeller: A propeller that resides in a pump housing and creates thrust for a personal watercraft. Impellers, better known as propellers when unshrouded or not placed within a duct, are a product of an extensive evolutionary process. Current generation impellers are a combination of the Archimedian screw (similar to a helicoil) and Conoidal propeller (sections of the helicoil removed).
    Intake grate or scoop grate: A grill-like component that mounts on the bottom of a hull and feeds water to the jet pump while also preventing foreign objects from entering
    Intake stuffer: A funneling device that mounts in the intake tract to increase velocity
    Jet pump or pump: The veined, cylindrical component which directs the flow of thrust created by the
    impeller.

    Kick: The area nearest the trailing edge of the blade that adds more pitch relative to its original chord.
    Leading edge: That part of the impeller nearest the front of the pump.
    Mixed flow: A pump with an impeller in a tapered housing, where water flow has some incline to the impeller access. This adds centrifugal force to the water as it is pressurized by the water. The pump housing collects the pressurized water and directs it aft in a high-speed stream.
    Overlapping blades: The amount of blade surface covered or hidden by another blade when viewed from the front or rear of the impeller.
    Parabolic rake: The off-center development of a concave area on the blade.
    Pitch: The theoretical travel of the impeller through a mass per revolution. Common with boat propellors, but not as accurate with PWC impeller designs. This is the actual blade angle measured along the outside diameter of each blade.
    Progressive pitch: The pitch increases from the leading edge to the trailing edge. Most impeller made now are designed this way.
    Pump nozzle or nozzle: A cone-shaped device which attaches to the back of the jet pump and pressurizes the flow of water.
    Rake: The angle of the impeller blade in correspondence to the impeller shaft or hub.
    Ride plate: A flat piece of metal that covers the cut-out for the pump. The craft "rides" on this plate.
    Slip: The difference between actual and theoretical travel of a blade and the loss of efficiency created.
    Stators: The directing vanes located immediately aft of the trailing edge of the impeller that re-direct spiraling flow into straighter trajectory.
    Straight pitch: The pitch is constant from the leading edge to the trailing edge of the impeller. Rarely used with current impellers made.
    Sweep/skew: The radius of the leading edge in relation to the hub.
    Top loader: A type of intake grate that utilizes a wedge perpendicular to the grate's parallel bars, in order to scoop more water up into the top half of the pump. This loads the pump more evenly.
    Trailing edge: That part of the impeller nearest the rear of the pump.
    Variable pitch: The pitch increases from the leading edge to the trailing edge, and from the hub to outer tip.
    Ventilation: The induction of air into the intake gullet due to excess speed or lift, thus breaking vacuum.
    Venturi: The shroud aft of the stators that compresses (accelerates) water to a greater velocity.



  6. #16
    scott2640's Avatar
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    Wow crazyA, that's a great start thanks.

  7. #17
    Connecticut CrazyA's Avatar
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    Thanks goes to Impros for that list.

  8. #18
    Connecticut CrazyA's Avatar
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    Many of these won't help with today's newer 4-Stroke super-skis, but none the less, knowledge is power !!!
    lol




    Advance curve: The amount the ignition advances as engine rpm increases.

    Advanced timing: The setting of the ignition system to fire earlier, or faster, than set by the factory.
    Aftermarket: The segment of the industry that manufactures replacement parts for stock watercraft (or putting groceries in your car).
    Air/fuel mixture: The combination of air and fuel droplets that is ignited in an engine.
    Amateur: A non-professional personal watercraft racer.
    Amperage: The intensity or strength of an electrical current.
    Ampere: The unit that amperage is measured in.
    Ampere hour: A battery capacity rating.
    Anneal: To heat metal and gradually cool it.
    Axial flow: A jet pump that pushes the water out in line with the pump centerline. Guide vanes are used to straighten the flow of water from the impeller, and eliminate torque reaction which can cause the craft to roll during acceleration.
    Base gasket: The gasket used to create an airtight seal between the cylinder and the crankcase.
    Beginner: A rider or racer with little or no experience (or PWI Associate Editor Chris Jonnum).
    Bilge: The inside bottom of a craft's hull, and the water that collects there.
    Bilge pump: A pump (either mechanical or electrical) to remove bilge water from the inside bottom of a craft's hull.
    Blue book: A book that lists craft models by year and gives a range of current value for their condition.
    Boarding platform: The area at the rear of a runabout or sport craft's deck, where a rider climbs on.
    Bond line: The imaginary line around a craft where the hull and the deck are joined together (or when Agent 007 propositions a female).
    Bond flange: The overlapping mating section where the deck and hull are joined together (or the waistline of 007).
    Bore:The internal diameter of a cylinder or hole (or PWI Associate Editor Jeff Hain).
    Bow: The front or forward end of a personal watercraft.
    Bow eye: The hole in a bow, used to secure a craft to a trailer, boat, or dock.
    Bulkhead: A structural reinforcement built into a craft's hull.
    Bumper: The plastic padding affixed to a bond flange to provide protection in small collisions (usually well-used on PWI Senior Editor Paul Carruthers' boats).
    Buoy: An inflatable object used to mark a turn on a race course (or a young male child).
    Butterfly: A disc-shaped valve within the throat or body of a carburetor.
    Bypass: A fitting used to route water away from the cooling system to a visible location, to dry out the exhaust system and allow a visual inspection of the system's function (or what PWI Lab Technician Dennis Greene will need if he doesn't stop smoking).
    Capacitor discharge ignition: A self-powered ignition which relies on the quick discharge of a capacitor to fire the spark plugs.
    Carbon fiber: A lightweight material composed by adding resins to graphite cloth. Often used to build race hulls.
    Carburetor: A device used to combine gas and air into an explosive vapor.
    Carburetor throat: The main passage or bore of a carburetor.
    Carburetor venturi: The hourglass-shaped center of certain carburetor throats.
    Cast: To melt metal and then pour it into a mold.
    Cavitation: A formation of cavities or pockets of air, which often occurs in the jet pump (or what happens if you don't brush your teeth).
    Center of gravity: The point in an object around which its weight is evenly balanced.
    Chine: A longitudinal member lying along the bottom side of the hull (not to be confused with the most populated country in the world).
    Choke: A valve that is used to reduce the air supply to an engine during starting (or what PWI Associate Editors Chris Jonnum and Jeff Hain do to each other when on deadline).
    Circlip: A semi-circular retaining clip used to hold the wrist pin in a piston.
    Clearance: The distance between two parts or surfaces.
    Closed-course race: A competition in which entrants race several laps around a buoy-marked track.
    Combustion chamber: The space in an engine where fuel is ignited and burned (or Carruthers' office during deadline).
    Compression: A reduction in the volume of gases within an engine's cylinder.
    Connecting rod: The metal bar that connects the piston to the crankshaft.
    Convergent cone: The rear, metal cone of an expansion chamber for a two-stroke exhaust system.
    Coupler: A part or device used to connect the crankshaft to the driveline on a personal watercraft.
    Course marshall: An on-water official who helps control the race and assists stopped riders on the course.
    Crankcase: The metal case that forms the bottom section of an engine, housing the crankshaft (or what Carruthers is during deadline).
    Crankshaft or crank: The flywheel and shaft assembly of an engine.
    Crankshaft axle: Either one of the two outer ends of a crankshaft.
    Crankshaft flywheel: The heavy wheel that is attached to a crankshaft for balance.
    Crankshaft journal: The bearing surface of a crank pin or crank axle (or Carruthers' diary).
    Cylinder: The chamber in which the piston travels up and down in an engine.
    Cylinder head: The upper part that is fitted on top of the cylinder, and houses the spark plugs.
    Cylinder port: An opening in a cylinder.
    Cylinder sleeve: The inner liner or section of a cylinder.
    Damper or dampener: A rubber or urethrane device that deadens or stops shocks within the driveline coupler.
    Deck: The upper structural body of a watercraft, located above (and including) the upper bond flange (or what Carruthers does to Hain when he misses a deadline).
    Decibel: A measurement of the relative intensity of noise or sounds (Hain has a high-decibel rating).
    Detonation: An improper type of explosion (usually caused by preignition) within the combustion chamber.
    Divergent cone: The metal cone of a two-stroke engine exhaust system (also called the “diffuser cone”).
    Dome: The spherical portion of a combustion chamber (or Carruthers' head in a few years).
    Drain plug: A device of various materials constructed to block the drainage of a compartment.
    Drive shaft: A shaft that connects the engine to the jet pump.
    Dry suit: A watertight, Michelin Man-like outfit worn when riding in extremely cold conditions.
    Electrolyte: A solution that will conduct an electric current within a battery.
    Engine block: The main part of an engine. It contains the cylinders.
    Engine plate: What mounts the engine to the motor mounts.
    Exhaust manifold: The waterjacketed portion of an exhaust system that connects the head pipe to the cylinder.
    Exhaust pipe: A large-diameter metal tube used to carry exhaust gases, pressure waves and sound waves away from the exhaust manifold.
    Exhaust port: The opening in an engine through which exhaust gases exit.
    Exhaust valve: An electronically or mechanically controlled valve that adjusts the height of the exhaust port according to rpm or exhaust pressure.
    Expansion chamber: A long, metal chamber in an exhaust system.
    Factory: A watercraft manufacturer's headquarters.
    Factory racer: A competitor that is directly sponsored by a manufacturer.
    Factory race team: A squad of riders and technicians that is directly sponsored by a manufacturer.
    Factory sponsor: A company that pays money or supplies product in order to be officially affiliated with a factory team.
    Fiberglass: Fine, flexible filaments of glass. When combined with resin, it makes up the material used to manufacture some watercraft hulls.
    Flame arrestor: An air cleaner that will not permit a flame to escape through its element.
    Flywheel: A weighted wheel on the end of the crankshaft used to trigger the ignition system, and generate current for the battery. It also houses the ring gear used to start the engine (or what happens when you don't tighten your lug nuts).
    Flywheel magneto: A system that utilizes magnets mounted to a flywheel to produce an electrical charge (or really cool rims).
    Footwell: On a runabout or sport craft, the platform area where the rider's feet go.
    Forge: To form metal by heating it, and then hammering it into shape.
    Freestyle: A competition in which entrants are judged during a two-minute routine of tricks and maneuvers.
    Fuel filter: A device used to prevent dirt and foreign objects from passing through the fuel system.
    Fuel injection: A method of pumping pressurized, vaporized fuel into internal-combustion engine cylinders.
    Girdle kit: A set of studs that passes through the cylinder block, pulling the engine cases and the cylinder head together (or something Hain wears while riding watercraft).
    Gunwale: The vertical walls that surround the tray or footwells of a personal watercraft (or a very large rifle).
    Handlepole: On a ski (standup craft), the pivoting arm that supports the handlebar.
    Head gasket: The seal that is used to join the top of an engine cylinder and the bottom of a cylinder head.
    Head pipe: The chamber (usually waterjacketed) that is directly connected to the exhaust manifold of an engine.
    Homologation: The process of officially approving, confirming or allowing a component or watercraft to compete in IJSBA events.
    Hull: The lower structural body of the watercraft located below (and including) the lower bond flange.
    Idiot light: A warning light that goes on when something in the system goes wrong (low oil level, engine overheating, etc.) (also known as a Jonnum light).
    Idle: The lower operating speed of an engine that is running (or what Hain is the majority of the time).
    Ignition: A mechanism or system used to provide and control the spark that ignites the fuel vapors within an engine.
    Ignition coil: An induction coil that acts as a transformer in the ignition system by converting low-voltage electricity into high-voltage electricity.
    Ignition timing: The speed and order in which the spark is provided to the cylinders to ignite the fuel/air mixture.
    Ignitor: The control (brain) unit of a CD ignition system. Often referred to as the “black box”.
    Impeller: A propeller that resides in a pump housing and creates thrust for a personal watercraft.
    In-line twin: A two cylinder engine with its cylinders in a row.
    Intake grate or scoop grate: A grill-like component that mounts on the bottom of a hull and feeds water to the jet pump while also preventing foreign objects from entering (or a good meal).
    Intake manifold: The element of the intake system between the engine block or crankcase and the carburetor, which channels the air/fuel mixture between the two.
    Intake port: An opening through which the air/fuel mixture is taken into an engine (or Hain's mouth).
    Intake stuffer: A funneling device that mounts in the intake tract to increase velocity (or Hain during an all-you-can-eat lunch).
    Intake tract: The complete system of related parts and areas involved in taking the air/fuel mixture from the carburetor into the engine (or Hain's throat).
    Jet pump or pump: The veined, cylindrical component which directs the flow of thrust created by the impeller.
    Keel: The lower-most point along the centerline of a V-shaped hull (or what Hain threatens to do to Carruthers during deadline).
    Kill button: A button connected to a switch that stops the ignition.
    Labyrinth seal: A two-stroke engine crankshaft seal with staggered grooves.
    Lanyard: A short chord which connects from the rider to the kill button so that the engine will stop running in the event of a get off.
    Life jacket or life vest: A buoyant device worn by the rider to provide flotation in the event of an emergency. Also referred to as a personal flotation device (PFD).
    Liquid cooled: Cooled by a liquid such as coolant, water or oil.
    Magneto: A system consisting of a small, electrical generator that uses a magnetic field to produce electrical current (or really cool wheels).
    Mixed flow: A pump with an impeller in a tapered housing, where water flow has some incline to the impeller access. This adds centrifugal force to the water as it is pressurized by the water. The pump housing collects the pressurized water and directs it aft in a high-speed stream.
    Moto: One of two or more races which are combined to determine an overall winner.
    Motor mount: The rubber damper used to bolt the engine into the hull.
    Musclecraft: A craft which uses a large-displacement engine (or what you do when you don't have a tote).
    Neoprene: A synthetic rubber used to make wetsuits.
    Oil injection: An engine lubrication system that pumps oil from a reservoir into the intake manifold or carburetor.
    Offshore: An endurance watercraft race which uses a long course.
    Paddle throttle: A wide, trigger-like hand lever, mounted to the handlebar and operated by either the finger or the thumb, which actuates the carburetor butterfly valve.
    Passenger: Someone on a watercraft in addition to the driver.
    Performance runabout: A sporty, race-oriented runabout watercraft.
    Personal watercraft: A vessel which uses an inboard motor powering a water jet pump as its primary source of motive power. It is designed to be operated by a person sitting, standing, or kneeling on the vessel rather than inside it.
    Piston: An aluminum, cylindrical piece that moves up and down in the cylinder, providing compression. (Dennis “The Worm” Rodman used to be one.)
    Piston ring: A round, metal piece that fits in the groove around the upper part of the piston. It creates a tight fit between the piston and the cylinder wall, which makes internal compression the engine possible.
    Port: The left-hand side of a craft, or an opening in an engine cylinder.
    Premix: A gas/oil mixture which provides lubrication to internal engine components.
    Pro: The highest category of personal watercraft racer.
    Pump nozzle or nozzle: A cone-shaped device which attaches to the back of the jet pump and pressurizes the flow of water.
    Qualifier or heat race: A preliminary race held to determine which riders will advance to the main event.
    Race gas: High-octane fuel, formulated especially for high-compression, high-rpm racing engines.
    Reed petal: A thin, fiber or metal plate that fits on a reed cage. The main component of a reed valve.
    Reed valve: A valve used for fuel/air induction into certain two-stroke engines.
    Reed stop: The metal portion on a reed block.
    Reed stuffer: A wedge-shaped device that fits into the reed cage and increases the air/fuel velocity.
    Resonator: A device in an exhaust system that uses reflection to mix sound waves and reduce the decibel level.
    Retard curve: The amount the ignition retards as the engine rpm changes. (or any corner that PWI Senior Editor Paul Carruthers takes on his craft).
    Retard timing: To set the ignition timing so that the each spark plug fires later during the piston's travel upward on the compression stroke (or Carruthers running a stopwatch).
    Rev limiter: A device which prevents the engine's rpm from going above a certain speed.
    Ride plate: A flat piece of metal that covers the cut-out for the pump. The craft “rides” on this plate.
    Ride tray or riding platform: On a stand-up craft, the platform where the rider's feet go.
    Runabout or sit-down: A personal watercraft that is designed for one or more people and has a seat. According to IJSBA rules, it must weigh more than 340 pounds, be shorter than 126.0 inches, and have a hull width between 38.0 and 50.0 inches.
    Sanction: An agreement between an organizing body and a promotor, that stipulates specific criteria to be met by the promotor in exchange for that body's support.
    Seizure: The grasping or binding of something. Happens to certain internal engine parts, when overheated or lacking proper lubrication.
    Sheet-molding compound: The material used for building the hulls of most watercraft. It is a combination of fiberglass mat and polyester resin.
    Ski or stand-up: A personal watercraft that is designed for one person to stand on and is controlled from a pivoting handlepole. According to IJSBA rules, a ski must weigh more than 225 pounds, be shorter than 120.0 inches long and have a hull width between 20.0 and 30.0 inches.
    Slalom: A watercraft competition in which entrants are clocked one at a time as they zig-zag through a buoy course.
    Spark plug: A device used to ignite the air/fuel mixture within the combustion chamber.
    Spark plug gap: The distance between the spark plug's center electrode and its side electrode.
    Sponson A special planing surface which may be integrated or attached to the hull's sides or transom.
    Sport: Personal watercraft which are designed for one or more people and have a seat. They can be ridden in either the sit-down or stand-up body position. According to IJSBA rules, a sport craft must be greater than 250 pounds, less than 120 inches long, and have a width between 26.0 and 38.0 inches.
    Spring suit: A wetsuit that features short legs and short sleeves, for riding in hot weather.
    Staging area: The area near the starting line where personal watercraft and their riders wait for their scheduled race.
    Starboard: The righthand side of a personal watercraft.
    Starter motor: An electric motor used for starting a watercraft engine.
    Steering cable: The cable used to connect the steering system (handlebar) with the steering nozzle.
    Steering nozzle: The portion of the pump which pivots left and right to control the direction of thrust and steer the watercraft.
    Steering stem: The rotating shaft to which the handlebar mounts.
    Stern: The rear, aft end of a personal watercraft (or what Carruthers is during deadline).
    Stinger: The small-diameter rear section of an expansion chamber.
    Strake: A continuous ridge which extends along much of the length of a hull's bottom. It is used to improve tracking and cornering, as well as providing lift.
    Tech inspector: The person who checks all competing watercraft for rule compliance and eligibility.
    Three-seater: A sit-down runabout craft designed to carry three people.
    Throttle: Any valve used to regulate the flow of air/fuel to an engine (Jonnum's has cobwebs on it).
    Throttle cable: The cable used to connect a throttle lever to the carburetor's throttle-valve linkage.
    Thumb throttle: A throttle-actuating lever mounted on the handlebar and operated with the thumb.
    Top loader: A type of intake grate that utilizes a wedge perpendicular to the grate's parallel bars, in order to scoop more water up into the top half of the pump. This loads the pump more evenly.
    Total-loss ignition: A watercraft electrical system with no charging system to recover electricity. It receives its electrical supply from the battery, which must be charged periodically.
    Tote: A balloon-tired cart used to transport watercraft short distances and across rugged terrain.
    Traction mat: A thin, rubber material bonded to the footwells, ride tray or boarding platform of a watercraft.
    Traction pad: A thick, rubber material bonded to the footwells, ride tray or boarding platform of a watercraft.
    Transfer port: An opening in the engine cylinder of a two-stroke watercraft engine, used to transfer the air/fuel mixture from the crankcase to the combustion chamber.
    Transom: The vertical, rear portion of the hull, which connects the sides and the bottom.
    Trigger pickup: On a total-loss ignition, the magnet-activated mechanism which signals the ignition coil to fire.
    Trigger throttle: A finger-actuated lever mounted to the handlebar and used to actuate the throttle valve.
    Trim: The up-and-down movement of the pump nozzle, which can change the hull's attitude.
    Triple cylinder: A watercraft engine with three cylinders.
    Twin cylinder: A watercraft engine with two cylinders.
    Two-seater: A sit-down runabout personal watercraft designed to carry two people.
    Two-stroke engine: A watercraft engine that draws an air/fuel mixture into its crankcase for primary compression. This happens as the piston travels upward to compress the already-transferred air/fuel mixture. Secondary compression, ignition and power result. On the downward stroke, the exhaust port is open, followed by the opening of the transfer ports. This action transfers the mixture from the crankcase to the combustion chamber.
    Velocity stack: A metal cylinder with a flare on its outer end, that is installed in the mouths of certain carburetors to make better use of air velocity.
    Waterbox: The final portion of a watercraft exhaust system, which mixes water and sound waves to muffle the exhaust noise.
    Waterjacket: A cavity and/or passage that allows liquid to pass in and around a designated area (for example, coolant in a watercraft engine circulates through a waterjacket).
    Wetsuit: A neoprene rubber outfit worn when riding in cold conditions.
    Wrist pin: The pin that allows the piston to pivot on the connecting rod.
    A or a: Ampere(s) or amperage.
    ABDC: After bottom dead center.
    AC: Alternating current.
    ACV: Alternating current voltage.
    AH: Ampere hour(s).
    APBA: American Power Boat Association.
    ATDC: After top dead center.
    Amp hr: Ampere hour(s).
    BBDC: Before bottom dead center.
    BDC: Bottom dead center.
    BIA: Boating Industry Association.
    BNG: Bold new graphics.
    BTDC: Before top dead center.
    cc: Cubic centimeter(s).
    Carb: Carburetor.
    CDI: Capacitor discharge ignition.
    CG: Center of gravity.
    dB: Decibel
    DC: Direct current.
    DCV: Direct current voltage.
    DNR: Did not race.
    DNQ: Did not qualify.
    DNF: Did not finish.
    DQ: Disqualified.
    Dyno: Dynamometer.
    ECU: Electronic control unit.
    EPA: Environmental Protection Agency.
    FRP: Fiberglass reinforced plastic.
    fl oz: - Fluid ounce(s).
    HIN: Hull identification number.
    HP: Horsepower.
    IJSBA: International Jet Sports Boating Association.
    IMTEC: International Marine Trades Exhibit and Convention.
    LCQ: Last chance qualifier.
    mm: Millimeter.
    mph: Miles per hour.
    OE: Original equipment.
    OEM: Original equipment manufacturer.
    oz: Ounce(s).
    PFD: Personal flotation device.
    PSI: Pounds per square inch.
    PWC: Personal watercraft.
    PWI: Personal Watercraft Illustrated.
    PWIA: Personal Watercraft Industry Association.
    qt: Quart(s).
    R/A: Runabout.
    R&D: Research and development.
    rpm: Revolution(s) per minute.
    SAE: Society of Automotive engineers.
    SMC: Sheet-molded compound .
    TDC: Top dead center.
    V: Volt(s); voltage.
    VE: Volumetric efficiency.
    WFO: Wide #*&@$% open.
    WFQ: World finals qualifier.

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  10. #19
    Connecticut CrazyA's Avatar
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    Some engine, porting and expansion chamber terminology. Again, a lot of this is older stuff and won't pertain to today's 4-Stroke Transformer skis, but still good terminology to know. I have not read or scanned this for accuracy.




    Porting Terminology




    Engine Terminology


    Nicasil = Nikasil = NiCaSil = NiComm - A combination of nickel, silicon, and carbide are electro-plated to an aluminium cylinder and then diamond honed to a precise diameter. The advantage of this process is increased heat transfer and less weight compared to steel/cast sleeves. Note: There are several proprietary processes of applying nickel silcon carbide to aluminium cylinders. For lack of a better term; Nicasil, is like saying "Ski-Dooing," instead of "Sledding."

    Top Dead Center (TDC)
    - The top of the piston's stroke.


    Bottom Dead Center (BDC) - The bottom of the piston's stroke.

    Deck - Top of Cylinder or Sleeve.

    Deck Height - Top of cylinder down to top of piston "negative deck."

    Positive Deck - If piston is above top of cylinder.

    Squish Clearance - Verticle distance between top of piston and head. Measured at the edge of piston. See "Squish Test" for measuring with soft lead solder over wrist pin.

    Effective Stroke - The distance from TDC to where the piston starts to open the exhaust port. (Also called: Power Stroke) A longer effective stroke helps low-end power and helps maintain compression at high altitude.

    Swept Volume - Volume of cylinder with piston at exhaust port opening to TDC. (4-stroke would be volume/cc's displaced by piston from BDC to TDC.)

    Trapped Volume - Volume of combustion chamber with piston at TDC.

    Compression Ratio (CR) - Volume of cylinder and combustion chamber with piston at exhaust port opening, divided by, volume of combustion chamber with piston at TDC. This is the "corrected" compression ratio. Most accurate way is to "cc" with a syringe or burette. Note: Power valves will change CR until valve is wide open.

    BMEP - Brake Mean Effective Pressure.

    Porting and Port Timing Terms

    Port - Air passageway/duct that is cast and/or machined into the cylinder.

    Port Window - The part of the port that opens into the cylinder bore.

    Exhaust Port - The large port where the burnt gasses exit the cylinder.

    Bridged Exhaust Port - Exhaust port with a center divider.

    Sub-Exhaust Ports - The small exhaust ports on each side of the main exhaust port. Measure at "choke point" not necessarily the port window.

    Triple Exhaust Ports - One main exhaust port with one sub exhaust port on each side.

    Transfer Ports/Ducts - The air passageways that allow the air/fuel mixture to transfer over the top of the piston to fill the cylinder.

    Main/Front Transfers - The 2 transfer ports located closest to the exhaust port (5 port).

    Secondary/Rear Transfers - The 2 rear transfer ports located closest to the boost port(s) (5 port).

    Boost Port(s) - The port or ports that are located opposite of the exhaust port and in-line with the intake port. These ports are usually angled sharply upwards to help scavenging.

    Auxiliary Transfers - Some cylinders have another set of transfers located between the front and rear sets (7 port).

    Transfer Base - Where the air enters the ducts/passagways at the bottom of cylinder & top of crankcase.

    Crank Angle - Crankshaft rotation measured in degrees. Total = 360 degrees.

    Port Timing - Degrees of crankshaft rotation after TDC to where port starts to open.

    Duration - The number of degrees of crankshaft rotation that a port is open.

    TA = Time-Area = TimeArea - The time and area required for a phase of the 2-stroke cycle at a specific RPM and BMEP. Examples: Transfer Port TA, Exhaust Port TA, Blowdown TA, and Intake Port TA.

    Port-TimeArea - The amount of time and area required for a port to flow the necessary air at a specific rpm and BMEP. The higher an engine rpm and/or pressure (BMEP) the more TimeArea required.

    Chordal Width = 90 degrees to Gas Flow or shortest straightline distance between sides.

    BlowDown - Measured in degrees of crankshaft rotation from Exhaust Port opening to the Transfer Ports opening.

    BlowDown TA - Must allow the cylinder pressure to drop below the pressure of the fuel air mixture at time of transfer ports opening. If the Blowdown pressure is to high when transfer ports open, it will stall or reverse, the incoming charge of fuel and air.

    LowBlow Width - Width of exhaust port when transfer ports open. Used to calculate BlowDown TimeArea.

    Port Height above BDC - With piston at BDC, measure from bottom of port, or piston, depending on which is higher, to top of port roof.

    Port Roof Angle - The angle of the top of the port at the window. Flat ='s 0 degrees.

    Scavenging - The process of pushing the burnt gas out of the cylinder and combustion chamber with a fresh fuel air charge. The transfer ports shape and direction of flow determines how the fresh charge will fill the cylinder and combustion chamber without short circuiting out the exhaust port. A good pipe will help the scavenging process.


    Tuned Pipe Terms

    Tuned Length - Total length from piston to end of baffle cone and start of stinger. All measurements made down centerline of pipe.

    Header - Exhaust flange to Diffuser. The header is usually a constant taper cone between 2 and 3.5 degrees. Approximately 30% of tuned length.

    Diffuser - The Diffuser Cone starts at the header with increasing divergent angles to the Dwell. The diffuser is approximately 28% of tuned length.

    Dwell - Center portion of pipe with parallel sides. Approximately 18% of tuned length.

    Baffle - Tapered cone from the dwell to the stinger that reflects the wave back to the piston. Approximately 22% of tuned length.

    Stinger- Stinger or Tailpipe provides the backpressure to amplify the wave back to the piston. Stinger length and diameter determine how the back pressure is built.

    Some Considerations: To much backpressure and the heat will build and the engine will burn down. Not enough backpressure and the engine will not make power. Wide open lake racing requires less backpressure due to heat build up in pipe over time. Drag racing and hillclimbing need more backpressure due to short time wide open and off/on throttle.

    High altitude needs more backpressure due to less air as elevation increases. We use a restricter bolt in the stinger at the end of the baffle cone to set the backpressure.




    Heads and MSV

    MSV - Maximum Squish Velocity rates the maximum velocity of the fuel air traveling across the squishband just before the piston reaches TDC. If MSV is to low the flame front will not burn the fuel air mixture effectively. If MSV is to high, detonation will occur and cause engine damage. The TSR programs calculate MSV for various types of heads.

    Tub Head - Shape of the combustion chamber - like a tub or hat.

    Hemi Head - Hemispherical shape for the combustion chamber.

    Squish Band - Outer area of head that forces the unburned fuel air mix into the center chamber for combustion. The squish band angle is usually 1-2 degrees greater than the angle of the piston dome. Verticle clearance and squishband width affect MSV.

    Squish - Verticle distance between top of piston and head. By measuring the step in the head and subtracting this number from the squish clearance you will have the distance the piston is below deck (negative deck). The negative deck measurement is needed to calculate port timing.

    Squish Band Area - Varies from 30% - 60% of Bore area.

    Step or Step Cut - The step cut in the head at the bore diameter. The squish band angle starts at the bottom of the step cut in the head. Measure the depth at the very edge of the step cut.

    Note: Some heads have the step cut diameter 0.020"-0.030" thou more than the bore diameter. This allows the head to be offset to the piston. This creates less verticle clearance on one side. By moving head back and forth, leave extra clearance over exhaust port side. Then, center the head, by doing a squish test, on each side of the piston, over the wrist pin. Try to get the variation to within 0.001" thou. This is important if you are running near the mechanical limit for verticle (Squish) clearance.


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