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  1. #1
    Join Date
    Nov 2004
    Location
    Seven Hills (Cleveland), Ohio
    Posts
    347

    Default head shaving (cylinder of coarse)

    ok you guys, a lot of you talk about shaving your head down to gain more compression. my dad has a mill at work and is able to do this for free so i thought why not, but i need details as far as how much to shave, gas needed for this mod (where to get race gas if needed), power increase, reliability issues, or anything else like that. FILL ME IN!!!!!! :p:
    '86 250r

    (Please Buy me!!!!!!)'85 lt250r

  2. #2
    Join Date
    Oct 2004
    Location
    Kewaunee, Wisconsin
    Posts
    3,441

    Default

    Ha ha very funny shaving a cylinder head...of course i'm the one that gets the head shaved lol...

    I'm not positive on r's, but I know that on shee's once you get 19cc domes you gotta run race fuel....

    And I think that .03 is = 1cc....if you shaved it I"de reccomend 93 octane just to stay on teh safe side..sorry I couldn't help much
    Saul
    1998 Yamaha Banshee

    Something sick in the making...out of frame pipes...plus 12 swinger...40's...

    2005 MXZ 800x PowerTek
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    E2S militia member

  3. #3
    Join Date
    Nov 2004
    Location
    Seven Hills (Cleveland), Ohio
    Posts
    347

    Default

    im running 93 octane now anyways
    '86 250r

    (Please Buy me!!!!!!)'85 lt250r

  4. #4
    Join Date
    Nov 2004
    Location
    Seven Hills (Cleveland), Ohio
    Posts
    347

    Default

    ok, another question is what is the stock head size for an LT???
    '86 250r

    (Please Buy me!!!!!!)'85 lt250r

  5. #5
    Join Date
    Dec 2004
    Location
    ar
    Posts
    369

    Default

    if it were my bike i would hold off. save some cash and get the cyl and head worked over as a set.
    twice the power, half the time.

  6. #6
    Join Date
    Nov 2004
    Location
    Wester, Pa.
    Posts
    1,390

    Default

    Theirs a whole lot more to gaining performance and compression than just shaving the head or deck height ...Theirs a couple little things that come in to play , Squish band (this must be reconfigured when shaving the head ) ,Piston deck height, Base gasket thickness , head gaskets thickness , piston style and brand, All these plus port height and timing and Ignition timing come in to play when figuring out comp. and Octane needed to operate with out detonation......Pretty simple Ha!
    official thief and loser of everything2stroke

  7. #7
    Join Date
    Oct 2004
    Location
    pennsylvania
    Posts
    14,217

    Default

    a good head rechamber is recomended after heads cut to improve squish band
    the dome mod is not a must do,but definitly will compliment cut head and is often considered just as important or more important than cutting head ,but as long as you dont take off too much you can safely cut the head for pump gas. for a generic all around ansewer if you have the stock stroke and piston and mild porting or stock porting you can be safe by screwing a plug in head tightly. pinch that in the mill vise ,have your dad indicate head flat across its surface in the vise.get a decent 2" flycutter skim .025 off @ 1200 rpm on mill . deburr and radius new edge and polish the shit out of your dome ,this should will give you a few ponies that will most likely be felt on bottom of powerband and still run 93 octane . dont go anymore than .025 without rechambering or your piston may hit !!!!!!
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  8. #8
    Join Date
    Nov 2004
    Location
    Seven Hills (Cleveland), Ohio
    Posts
    347

    Default

    thanks you guys, if theres anybody else with input on this, please dont hesitate to respond. i dont want to end up doing the wrong thing here.
    '86 250r

    (Please Buy me!!!!!!)'85 lt250r

  9. #9
    Join Date
    Nov 2004
    Location
    Seven Hills (Cleveland), Ohio
    Posts
    347

    Default

    quick question, the squish band is the area is the area that is around the edge of the dome, where it is not really domed yet, correct??
    '86 250r

    (Please Buy me!!!!!!)'85 lt250r

  10. #10
    Join Date
    Nov 2004
    Location
    Wester, Pa.
    Posts
    1,390

    Default

    Here are some terms and deffinitoins that pertain to 2 strokes.....

    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.

    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.


    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). (ie Ct sonic blaster top Kit )

    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.


    This should help every one understand what porters and pipe builders deal with on a Day to day basis and the knowledge that is be hind those skilled crafts
    Last edited by Flattrack; 01-08-2005 at 06:08 PM.
    official thief and loser of everything2stroke