Chainsaw exspansion chamber/exhaust

Discussion in 'Performance Mods' started by Jake.B, May 15, 2012.

  1. Jake.B

    Jake.B New Member

    Hey guys im getting a Homelite C-72 chainsaw soon. Its 70-88 model but runs great. I want to put an exhaust system but Im not real familliar with 2-strokes. I get they need back pressure and that good stuff. I Want an expansion chamber with a silencer on the end depending on the noise level. I want to buy one that i can just fab up a flange. Anybody know where to get somthing like this?
     

  2. HeadSmess

    HeadSmess Well-Known Member

    arrrrgh!

    shut up about back pressure! its a myth perpetuated by ignorance!!!

    a REAL TWO STROKE EXHAUST CREATES NEGATIVE BACKPRESSURE.

    they can achieve a half atmosphere of vacuum! this SUCKS out the exhaust gasses!

    a real two stroke exhaust, also, confusingly, creates POSITIVE BACKPRESSURE (or just plain back pressure) also around, roughly, half an atmosphere.

    this pushes any fresh air/fuel that happened to get sucked out with the exhaust, back into the cylinder, compressing the mixture. 21 psi instead of standard 14 psi is a lot of boost. try setting a car with a turbo to 7psi boost and see how it goes compared to stock with no boost at all.


    now, the question.

    a homelite chainsaw. what capacity is the engine? any idea what the port timings are? is it reed valved or piston ported? these are things you really need to know.

    a tuned pipe is tuned to a specific design of engine. capacity, port times, intended rpm.

    there are very few bolt on upgrades, except for things common enough. a HT is common, so there are pipes available. a yz250 is common, there are a variety of pipes available, where as a chainsaw with a tuned pipe would just be awkward to use...usually the muffler is at the front, and thats where you bang up against tree trunks, so a pipe a foot longer than the bar would be in the way...

    all you can do is find out its capacity. then look around at pipes intended for bikes, scooters, whatever of roughly the same capacity. dont expect full out performance, but do expect a fairly large gain! they arent tuned for what you desire, or what the engine may require. but then a few centimetres of extra pipe or 2 or 3 degrees of ex port opening only affects a few hundred rpm...whereas a 20 degree difference and 20 cm would make a massive difference...

    ps, they are easy to make. ;)
     
  3. Jake.B

    Jake.B New Member

    Ok thanks, i know how a 2 stroke works i just never got the whole cones and things. That helped alot.

    Heres the info i could find:SERIES OR ASSEMBLY NUMBER:

    YEAR INTRODUCED:

    YEAR DISCONTINUED:
    1982
    ENGINE DISPLACEMENT:
    4.9 cu. in. (80.3 cc)
    NUMBER OF CYLINDERS:
    1
    CYLINDER BORE:
    2.0 in. (50.8 mm)
    PISTON STROKE:
    1.5625 in. (39.7 mm)
    CYLINDER TYPE:
    Aluminum with chrome plated bore
    INTAKE METHOD:
    Reed valve
    MANUFACTURER ADVERTISED H.P.:
    not advertised
    WEIGHT :
    18.5 lbs. (8.4 kg) powerhead only
    OPERATOR CONFIGURATION:
    One Man operation
    HANDLEBAR SYSTEM:
    Rigid
    CHAIN BRAKE:
    none
    CLUTCH:
    Centrifugal
    DRIVE TYPE:
    Direct
    CONSTRUCTION:
    Die cast magnesium
    MAGNETO TYPE:
    Phelon or Wico flywheel type
    CARBURETOR:
    Tillotson HL-141 series
    MAJOR REPAIR KIT:
    RK-88HL
    MINOR REPAIR KIT:
    DG-2HL
    AIR FILTER SYSTEM:
    Cellulose fiber element
    STARTER TYPE:
    Homelite automatic rewind with overrunning bearing clutch
    OIL PUMP:
    Manual
    OPERATING RPM:
    6,000 to 6,500
    IGNITION TIMING:
    Position stator plate fully clockwise
    BREAKER POINT SETTING:
    0.015 in. (0.38 mm)
    FLYWHEEL/COIL AIR GAP:
    Position is fixed
    SPARK PLUG TYPE:
    Champion J-6J
    SPARK PLUG GAP:
    0.025 in. (0.63 mm)
    CRANKSHAFT MAIN BEARINGS:
    Ball on flywheel side, caged needle roller on drive side
    FUEL TANK CAPACITY:
    49.3 oz. (1500 ml)
    FUEL OIL RATIO:
    32:1 with Homelite oil
    RECOMMENDED FUEL OCTANE:
    Regular grade
    MIX OIL SPECIFICATION:
    Homelite chain saw mix oil
    CHAIN PITCH:
    .404 in.
    CHAIN TYPE:
    Oregon 52C
    BAR MOUNT PATTERN:
    16 link
    SHORTEST GUIDE BAR SUPPLIED:
    17 in. (43 cm)
    LONGEST GUIDE BAR SUPPLIED:
    30 in. (76 cm)
    COLOUR SCHEME:
    Red and Green

    I think it reed valved, as it says "Intake method: reed valve" are there any other ways i can figure out the port timings?
     
  4. tooljunkie

    tooljunkie Member

    Dang!
    thats a big saw.
    .404 chain needs a lot of power to pull it.
    i was searching for info on my homelite 245 and came up blank.
    if you search "hotsaws" you may find what you are looking for.
    they are like dragsters in the chainsaw world.
    tuned pipes ,mikuni carbs overbored.
    timed races for sawing through logs.
    there's even a chevy small block powered chainsaw.
     
  5. Jake.B

    Jake.B New Member

    Thanks ill check it out.
     
  6. Neon

    Neon Member

    Ouch! I wouldn't even consider using a saw that large. I couldn't even begin to tell you how scary that would be once the midrange kicks in. You would probably want a pipe that would shift some of the power to the low end.
     
  7. Jake.B

    Jake.B New Member

    Checked out hot saws, did not find any parts to purchase.
     
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