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

  1. #1
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    How to pick a 400EX cam (a specification comparison)

    [I got tired of looking up this thread over and over so I'm putting it here so it will stay put. The original thread is HERE].

    I see a lot of questions about 400EX cams. I thought it might be helpful to have a list of many of the available cams with their specifications. I picked up these specs from various places...if anyone sees errors point them out. The Hotcams specs are straight off their website and I called them to get the specs for the old version of the stg 2.

    I won't comment on brand X vs. brand Y because I'm not qualified to do so. Also, I can't really comment on how cam X will perform in your quad because in most cases I don't specifically know that information. Instead, I've tried to put together some technical information that might help YOU decide what cam might suit you and your engine.



    On to the specs!!

    cam: Intake lift; Exhaust lift; Intake duration; Exhaust duration

    stock............... .316, .302, 234, 238

    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

    Notes:

    --Numbers are listed in inches and degrees of crank rotation (lift duration at approximately .050" lift).
    --The Hotcams stg 2 old version is identified by "HCDG NO. 08" etched onto the cam--not sure what the current version says. Hotcams part number for the old cam is 1008-2.
    --Valve clearance specs for all Hotcam cams are: intake .005", exhaust .006"
    --White Brothers All Around is etched with "WB1870".
    --White Brothers Track is etched with "WB1498".
    --Notice that the WEB 450/451, GT Thunder, and WB Track are all the same grind.
    --Honda part number for the HRC cam (it's actually an XR400 HRC cam) is 14000-NKK-000. I don't think they are still available from Honda.
    --Some retailers list a Hotcams Stage 3. This is an sometimes an erroneous label given to the "old" version of the Stage 2. Some retailers have stock on both the "old" and "new" versions and have to call the "old" version something, I guess. Other times the "stage 3" label is given to the stroker cam. So just be careful concerning the the "stg 3" label cause it could mean different things.
    --This is what Hotcams told me about the performance difference between the "old" and "new" versions: "...As far as the difference between the old stage 2, and the new stage 2, the new stage two still has a good top end gain, but doesn't loose as much on the bottom..."



    The lift is how far the cam opens the valve. The duration is how long it leaves it open. The more lift and duration the more aggressive the cam. Big lift and duration numbers work best at high RPM while more mild numbers are best for lower RPM.

    The more duration the intake valves have the more important it is to have a high(er) compression piston. This is because with lots of duration there is more opportunity for air to escape through the valves as the piston begins its compression stroke. Even on the stock cam, the intake valves are still open when the piston begins its compression stroke. With an aggressive cam some dynamic compression is lost through valves that stay open for a long time. This must be made up for with a higher compression piston. An aggressive cam with a stock compression piston may actually perform worse than the stock cam because too much compression is being lost through the valves being opened so much. I have personally seen this happen--dyno confirmed (although it wasn't a 400EX).

    Here's a theoretical example to help in understanding this concept:

    -bore: 85mm (stock)
    -static compression ratio: 9.1:1 (stock)
    -elevation: 1500ft
    -intake valve closes: 40deg ABDC (After Bottom Dead Center) (stock at 1mm lift)

    The resulting dynamic compression ratio is 8:1. Note that is a smaller figure than the static compression ratio we started with. Again, this is because the actual compression of the compression stroke doesn't really start until the intake valves close.

    Now, if we increase the intake valve duration to 55deg ABDC and leave the static compression ratio at 9.1:1, we get a new dynamic compression ratio of 7.4:1! In order to get the dynamic compression ratio back to where we started (8:1) with the increased intake valve duration we would need a piston with almost 10:1 static compression. Just for the heck of it I looked at how 5500 ft of elevation changes things. At 5500ft with the 55deg ABDC spec you'd need a 10.8:1 static compression piston to yeild an 8:1 dynamic compression ratio.

    Now, you might be thinking what's the point of adding a cam and a piston if doing both gets you the same dynamic compression ratio you started with?? Good question. The answer is that now you have the same dyanmic compression ratio you started with but also have the cam specs that will allow the engine to breath better. And in the real world, most piston choices are actually going to bump your dynamic compression beyond what it was stock even with the addition of a cam. A 10.5:1 piston with a cam (using the 55deg ABDC spec) would get you a dynamic compression ratio of 8.6:1--0.6 points higher than all stock.

    I used a dynamic compression ratio calculator to get those figures. I guessed on certain required values because there's some information I don't have. So, the above numbers are not quantitatively exact. But the relationship between static compression, dynamic compression, and intake valve timing IS accurate.



    Knowledge is HorsePower!

  2. #2
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    Thanks for consolidating this info GPracer

    Can you elaborate a bit on Duration and Lift and how they affect performance? i.e. How a relativly higher lift/shorter duration cam performes differently than a lower lift/longer duration cam.

    I'm not sure if this applies to the 400ex and similar motors though....
    ATVRiders Janitorial Technician


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  3. #3
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    Originally posted by JOEX
    Thanks for consolidating this info GPracer

    Can you elaborate a bit on Duration and Lift and how they affect performance? i.e. How a relativly higher lift/shorter duration cam performes differently than a lower lift/longer duration cam.

    I'm not sure if this applies to the 400ex and similar motors though....
    I'll try and answer with my current level of understanding:

    Increasing lift without increasing duration will normally yield more power throughout the RPM range. However, an increase in lift is almost always accompanied by an increase in duration.

    Lift and duration generally go up and down together because of practical limits governing the shape of the lobes. If you tried to have super high lift with moderate duration than the lobes would become prohibitively "pointy"--very tall but narrow. The ramps of the lobe (ramps are the transition zones on the sides of the lobe) can only be so steep for reliable valvetrain operation.

    Specific to intake valves, there is a limit to the speed of the intake charge before effiecency begins to drop off. That natural "speed limit" for the intake charge helps do define the lower limit of possible lift specifications for any given duration. Long duration with moderate lift would leave you with very high intake charge speeds. Go too fast and you start going backwards. That doesn't apply to the exhaust gases exiting the exhaust valves though. I'm not sure why.

    I hope that at least partially answers your question. I'm gonna stop there because I'm starting to get in over my head--I'm no expert on these matters.

    ETA: Actually, I probably should have stopped before I started...really, I'm an amature. I'd much rather we got answers from an expert.

  4. #4
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    you should sticky this. so many people ask about this.
    2005 Honda 416ex 11:1 Fan Cooled
    -HMF Full Exhaust
    -HotCams Stage 2
    -HD Cam Chain
    -Nerf Bars
    -ITP Holeshot's all around
    -K&N Air Filter
    -AC Racing Front Bumber
    -Renthal Sprockets and Chain

  5. #5
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    Messed up
    2005 Honda 416ex 11:1 Fan Cooled
    -HMF Full Exhaust
    -HotCams Stage 2
    -HD Cam Chain
    -Nerf Bars
    -ITP Holeshot's all around
    -K&N Air Filter
    -AC Racing Front Bumber
    -Renthal Sprockets and Chain

  6. #6
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    I wonder if this info is really helping the average joe make a choice. I feel like something is missing--but I'm not sure what.

    Where does valve overlap fit into this? Why don't cam manufactures publish overlap data? Is there away to evaluate the most efficient RPM (peak torque) for a camshaft from lift/duration numbers alone?

    Are there any engine builders that could enlighten us?
    "It ain't what you don't know that gets you into trouble.
    It's what you know for sure that just ain't so. "

    --Mark Twain

  7. #7
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    so how do you know what is the best rise heigth?

  8. #8
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    Originally posted by PowerJunkie
    so how do you know what is the best rise heigth?
    To the best of my understanding, it depends on how the rest of the engine is configured (porting, bore, compression ratio, etc.) and where you want the engine's power to be concentrated (low rpm vs. high rpm).

    I realize that answer may not help you make a decision. But when I try and elaborate more than I already have in the original post, I start becoming unsure of the accuracy of my advice...
    "It ain't what you don't know that gets you into trouble.
    It's what you know for sure that just ain't so. "

    --Mark Twain

  9. #9
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    do have any specs on the magnum cam

  10. #10
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    Originally posted by pimpin416ex
    do have any specs on the magnum cam
    I've looked and can't find squat. Last time I looked I couldn't even find a website for the manufacture....
    "It ain't what you don't know that gets you into trouble.
    It's what you know for sure that just ain't so. "

    --Mark Twain

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