4 degree timing sprocket

Discussion in 'Engine, Fuel and Exhaust' started by Redfish-Joe, Mar 8, 2011.

  1. Redfish-Joe

    Redfish-Joe Senior Member

    What are the pros and cons of this. Can any gain be expected without changing cams? I ride two up most of the time so a little more low end torque couldn't hurt.

    08 Road Glide
    SE slipons
    Stage One breather
  2. Jack Klarich

    Jack Klarich Guest

  3. Redfish-Joe

    Redfish-Joe Senior Member

    Thanks y'all.

    BUBBIE Well-Known Member

    The 4* +- gear is used USUALLY as a Tunning Device, when a Cam is Not performing as wanted or JUST to change ITS performance to ONE side or the OTHER...

    If you advance OR retard a cam, You are changing ALL the Design Timing of that cam... Earlier or Later

    Example; A SE255 cam (just looking at the Intake Close as ALL valve numbers will change out the same 4* +-)

    The intake(se255) CLOSES at 25*, That IS a Low *Number on intake closing and is a Sign of a Low End Torque Cam.

    Say you Want this cam to "Get Legs" (move rpm and power band UP) to a little HIGHER..... Hence You change the intake to CLOSE "OUT" (bigger number) a Little later...

    Closing Intake valve Later....using -4* cam gear makes the Intake close FROM 25* to close at 29*....(out)

    The other direction, +4* will close the cam intake EARLY at 21* which is WAY TOO early for a cam to close on a HD.... so a SE 255 cam is only moved out Using -4* timing to 29*...

    Now Lets take a BIGGER cam for example:
    (made for higher RPM and NEEDS More Compression to opperate properly)

    Say the intake valve closes at 40*,,, This tell me that this cam will develop Tq and HP at a Higher RPM band(not like the SE255's developing Tq at Lower RPM like 1800 to start)..
    Usually this Bigger cam 40* (later valve timing numbers) will state RPM band from 2600 to 6000 RPM (mind you,,, Just Examples here)..

    ALSO with that LATE of Valve closing 40* all valve timing LOOSE something in OVER LAP of each other..MEANING LOSS of COMPRESSION so to remedy, you needed to use Higher compression in your build some way,or Should have in selection of that cam.

    Now, you can use the 4* gear to change the INTAKE valve (all will move 4*) to close at 36* instead of 40* and again,you are RE-Timing the 40* cam to become a LESSER number on intake close to 36* (earlier).

    36* Starts Torque at LOWer RPM and cam coming "ON" SOONER in the RPM Band..and it will ALSO Increase Compression Ratio a TAD BIT=
    (more power)....

    So IF you do the REVERSE and Move the Cam OUT 4* and NOW the intake closes at 44*, You have a HIGHER RPM BAND as it won't come on Early in Lower RPM's (and even MORE compression is needed to OFF-SET the timing out difference)......
    So this being a Higher Duration Cam and the power band is streatched out to 6000 RPM.. Good for some Ride Styles, But I don't want to have to REV my bagger up to 2600 rpm to JUST START to "come up on the cams"

    so I'll stick with my se255 that pull early and peter-out early also...

    I do have a +-4* gear to play with some time but too good running with the SE255's for now.... I will change out the 25* to 29* when I go 103" Some Day...

    HOPE you Get the drift here......

    Many will ask, " Why not go with the correct cam in the first place"??

    Some times the Cams you seek will NOT be Exactly What and Where you want the power band and Choosing A cam that says 40* BUT wanting it in a 36*... using the +4* it Will be everything THAT 40* cam offers and YET Lets it "Come ON" Just a bit earlier (intake close of 36*)

    The SE255 cams closes at an EARLY 25* and with a Hefty .550 lift..(bolt in cams until .575 max lift) They Come on EARLY in the RPM band, getting Power Tq. at a Lower Starting RPM Point. and That makes it Just right for MANY bagger Riders...

    Now Steve07 took a BIGGER style Cam and Used the 4* gear to give HIS cam choice More Low End Power @ a little Lower RPM start point..

    He says he can Pull the front wheel off the ground EASILY..Thats Power. And starting Down LOW rpm where you need it.

    When picking a Cam, BIGGER is not always Better.
    A lot of thought goes into Selecting a Build that will work well andDon't Forget "YOUR riding style"...

    Cams are JUST a part of the build.. Compression, Piston size and Spark timing and Fuel, make a big difference..Selecting a PROVEN Build for Your RIDING STYLE is "KEY" here....
    You can't build a HIGH rpm bike motor using a LOW number INTAKE close and vice-A-versa so WHERE you want the Torque to "come-on" is Important...

    YOU CAN take a BIG number Cam and GET a LOT of LOW END POWER out of it, but it will Cost you in building a MONSTER to work well at Both Ends.

    RIDING STYLE, and model of bike takes in a Big Part of a build..


  5. Redfish-Joe

    Redfish-Joe Senior Member

    Thanks Bubbie.