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Thread: How to pick a 400EX cam (a specification comparison)

  1. #31
    Join Date
    Apr 2010
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    new spring feild
    Posts
    149
    ok i understand 3/4ths of it. but the dynamic and static comprestion. i wanna no what each one means.and witch on is the one that makes u have to run race gas or not.
    2000 400ex
    11:1 wiseco piston
    stg2 cam
    fmf slip on
    douglas wheels around
    gbc race rex tires
    ac nerf bars.
    maiger plastic
    pro taper s/e bars
    swinger skid plate
    450r fronts

  2. #32
    Join Date
    Oct 2002
    Location
    Nevada
    Posts
    9,647
    Originally posted by 250rforlife
    ok i understand 3/4ths of it. but the dynamic and static comprestion. i wanna no what each one means.and witch on is the one that makes u have to run race gas or not.
    Simple explanation. First off, we're not talking about compression readings, we're talking about the actual calculations.

    The compression ratio as you normally see it, like 9.4:1, is the STATIC compression ratio. Let's make up easy numbers. The "size" of the engine is the actually volume the piston moves, let's say it's 360cc. Let's also pretend this engine has a 40cc combustion chamber (the volume of space when the piston is at Top Dead Center, the volume when you're actually burning). The compression ratio is calculated as the TOTAL (360cc+40cc=400cc) divided by the combustion chamber (40cc). This engine would have a 10:1 compression ratio.

    However, the valves don't actually close when the piston is at absolute bottom, believe it or not, the air is still moving into the cylinder. The valve actually closes a little later, the piston has already started it's upward travel on the compression stroke. This is the Dynamic Compression. It's not when the piston is at the bottom, but the compression ratio when the valve actually closes.

    Let's pretend, in our same 360cc engine, that the piston has started to move up and takes up 20cc of that space before the valve closes. Now we have 380cc (340cc plus the 40cc combustion chamber) divided by our 40cc combustion chamber volume.

    380/40=9.5

    This is a far cry from our static of 10:1.


    As you can see, the static compression is based on the engine design alone. You can change it with pistons that take up more of the combustion chamber, but the dynamic compression actually changes based on the camshaft specifications, because different camshafts close the valves at different times.
    Duncan Racing 340PV, +2 A-arms, +4 LSR axle, and a host of other goodies.

  3. #33
    Join Date
    Dec 2006
    Posts
    259
    XR400.............. .326, .321, 240, 244
    HRC................. .350, .339, 254, 256
    GT Thunder....... .350, .345, 256, 256
    WB Track.......... .350, .345, 256, 256
    WB All Around.... .345, .335, 240, 248
    WEB 450/451..... .350, .345, 256, 256
    WEB 479........... .378, .378, 250, 250
    WEB 463/9i....... .385, .370, 272, 270
    Hotcams stg 1... .354, .354, 246, 246------Intake centerline 106, Exhaust centerline 107
    Hotcams stg 2... .354, .350, 254, 248.5----Intake centerline 106, Exhaust centerline 104.25
    HC stg 2 (old).... .348, .349, 254, 254------Intake centerline 106, Exhaust centerline 107
    Hotcams stroker. .358, .354, 262, 257------Intake centerline 110.5, Exhaust centerline 104.5
    Megacycle x1..... .346, .346, 246, 246
    Megacycle X2..... .378, .378, 254, 254
    Megacycle X6..... .402, .385, 270, 262

    I have a magnum cam and the #'s listed are the same as the gt thunder, wb track and web 450/451 not sure if there are any other specs to take into account hoping it was not a waste of money for a 416 mx build. I was wondering if a port job or should i go +1 valves and if 11-1 or 12-1 compression piston? Thanks

  4. #34
    Join Date
    Apr 2011
    Location
    GA
    Posts
    87

    Part #1043-2 stage 2 HC vs stage 1 HC

    How many guys are running the Part#1043-2 stage 2 HC on their (stock) 400ex's? I purchased one thinking it would be a good cam to have for my 4wheeler, but I have been reading that a stage 1 might be better suited. I have no desire to build the motor as I already have two other projects in the works.

    I'm just looking for a bolt and go operation for some weekend fun(trail riding). Would you guys recommend I sale the stage 2 and get a stage 1, or keep the stage 2? I will be running a LEXX muffler on a stock header with the tube welds dremeled out for a little better air flow.

    -mr34-
    04 400ex - Weekend Warrior
    93 SE-R - 2.3L big bore in progress
    01 G20T - Automatic tour ride

  5. #35
    Join Date
    Feb 2008
    Location
    Orange County, Ca.
    Posts
    3,069
    I posed this question to Steve, and mentioned a possible addition of the +6 key with a stage 2 cam, on the stock bore. surprisingly to me, the responce/opinion was quite different than I would have figured it.

    (I'll leave his exact responce out of it, in case HE would like to weigh in on it here).

    I'd really like to hear from both GPracer2500, and Wheelie,
    to see what their opinions on this would be comparatively...

    How would a 400EX stock piston/bore with a stage 2 hot cam, and a +6, timing key perform,...

    vs.

    a 400EX stock piston/bore with a stage 1 hot cam, and stock, (OR,... +6) timing key ?

    (Keep in mind, this question/comparison is for a STOCK Bore, STOCK Compression 400EX)

    GPracer, and Wheelie,..... would you guys mind weighing in on this ???

    Steve ??? Pipeless ??? Beags ??? Nacsmxer ??? ZRpilot??? wilkin250r???

    Thanks

  6. #36
    Join Date
    Apr 2005
    Location
    WI
    Posts
    8,922
    i will post my individual experiences with the keys, though it seems to be a bit different than some others.

    I feel that the keys help out top end with more advance.

    so a 6 degree with a stage 2 would result in more top end than a stage 2 with a stock key with the same setups for comparison. the low end falls off as a result of this timing advance also.

    i dont have any numbers or anything to back this up though, which is why i have issues with anything on the subject.

    just my experiences, thoughts?
    steve
    2019 Maverick X3 XDS Turbo R
    2003 TRX 400EX
    2016 HONDA RANCHER

  7. #37
    Join Date
    Aug 2010
    Location
    Cornell, Wisconsin
    Posts
    90
    speaking from experience, stage two cam on a stock motor makes it lazy and the power was not impressive at all.
    2003 400ex
    -namura 440 big bore kit
    -stage 2 hotcam
    -debaffled shorty stock exhaust
    -168 main jet
    -itp holeshots
    -outerwears shock covers
    -high bend bars
    -tether

  8. #38
    Join Date
    Dec 2010
    Location
    Wilkes Barre, PA
    Posts
    338
    I have Read trough this all and I cant make since of anything...

    I have a 100% Stock 01400EX with a slip on, what Cam and Piston should I run If I wanted to up mid - high but not really loose bottom end? If that if even possible...
    Lance

  9. #39
    Join Date
    Feb 2008
    Location
    Orange County, Ca.
    Posts
    3,069
    Originally posted by DirtyBirdRacing
    I have Read trough this all and I cant make since of anything...

    I have a 100% Stock 01400EX with a slip on, what Cam and Piston should I run If I wanted to up mid - high but not really loose bottom end? If that if even possible...
    on a stock bore, stock compression piston,...
    You'd probably be quite pleased with a HC stage 1.
    the stock compression does not really support the flow of a stage 2,....
    without sacrificing bottom end.

    Add to that, a Uni air filter, outerwears lid, +6 timing key, and a '04-'05 450r carb. (PROPERLY RE-JETTED of course)
    You will then be at 32 - 33 Whp,... (as compared to your 26-28 Whp now).

    See my carb comparison thread, ( in the stickies ).

    and before you even ask,.....
    NO,.... you will NOT gain anything with a aftermarket CDI, or coil. They are a complete waste of money, ESPECIALLY on a stock piston configuration.

    but before you do ANY of that,...
    You will be far better served,...
    With a pair of good front shocks.

  10. #40
    Join Date
    Dec 2010
    Location
    Wilkes Barre, PA
    Posts
    338
    Would it matter if I ran a K&N filter? sorry for got to mention that I was running that before

    Thanks for the help.


    Originally posted by tri5ron
    on a stock bore, stock compression piston,...
    You'd probably be quite pleased with a HC stage 1.
    the stock compression does not really support the flow of a stage 2,....
    without sacrificing bottom end.

    Add to that, a Uni air filter, outerwears lid, +6 timing key, and a '04-'05 450r carb. (PROPERLY RE-JETTED of course)
    You will then be at 32 - 33 Whp,... (as compared to your 26-28 Whp now).

    See my carb comparison thread, ( in the stickies ).

    and before you even ask,.....
    NO,.... you will NOT gain anything with a aftermarket CDI, or coil. They are a complete waste of money, ESPECIALLY on a stock piston configuration.

    but before you do ANY of that,...
    You will be far better served,...
    With a pair of good front shocks.
    Lance

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