New to the WRX. What to know? (2004 WRX) - Page 3
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This is a discussion on New to the WRX. What to know? (2004 WRX) within the New Member Hangout forums, part of the Community - Meet other Enthusiasts category; Originally Posted by kempobmx1 Right I pretty much understand why double clutching helps. What I want to know is why ...

  1. #31
    Registered User Micah's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    Right I pretty much understand why double clutching helps. What I want to know is why you can't just go *clutch in, neutral, match revs, clutch out* Why do you have to let off the clutch for the rev match in neutral?
    Because if you don't let off the clutch in neutral you are not double clutching. You are only rev matching, still not a bad idea - but it's not double clutching. Read the description I pasted above again from the wiki page if you still don't get it. Or ask anyone who has their CDL - it's supposedly a part of the test.

    Double clutching is a fine art of driving a manual transmission. Most people cannot do it. Some people can do it. Few people can do it fast, and very few people can do it fast reliably.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
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    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
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  3. #32
    Registered User kempobmx1's Avatar
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    Right. I can do it, but neither quickly, nor reliably. Than again the WRX will be the first standard car I've owned, so I'm not bad for such little practice.

    What I just don't get is, why double clutch instead of just rev matching while clutched in? Is it just for the art of double clutching or is there a functional reason?

  4. #33
    Registered User Micah's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    Right. I can do it, but neither quickly, nor reliably. Than again the WRX will be the first standard car I've owned, so I'm not bad for such little practice.

    What I just don't get is, why double clutch instead of just rev matching while clutched in? Is it just for the art of double clutching or is there a functional reason?
    Again - everything you need to know is in that paragraph I pasted earlier. I'll paste it again:

    The purpose of the double-clutch technique is to aid in matching the rotational speed of the input shaft being driven by the engine to the rotational speed of the gear you wish to select (directly connected to rotating wheels). When the speeds are matched, the gear will engage smoothly and no clutch is required. If the speeds are not matched, the dog teeth on the collar will "crash" or grate as they attempt to fit into the holes on the desired gear. A modern synchromesh gearbox accomplishes this synchronization more efficiently. However, when the engine speed is significantly different than the transmission speed, the desired gear is often unengageable even in a fully synchronized gearbox. An example is trying to shift into a gear while traveling outside the gear's speed or directional range, such as reverse while moving forward.
    Double clutching, although time consuming, eases gear selection when an extended delay or variance exists between engine and transmission speeds. When shifting up on a non-synchroniser equipped vehicle, the clutch pedal is pressed, the throttle is released, and the gearbox is shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the RPM will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manoeuvre can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.
    Read this until it sinks in.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  5. #34
    Registered User ScoobyWreXX's Avatar
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    Quote Originally Posted by Micah View Post
    Again - everything you need to know is in that paragraph I pasted earlier. I'll paste it again:



    Read this until it sinks in.
    : Hilarious. :
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  6. #35
    Registered User kempobmx1's Avatar
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    I understood it the first time. What it doesn't explain is why just clutching, rev matching while clutching, down shifting, then un-clutching doesn't do the same thing. I completely understand why double clutching works. I'm saying that, ignoring sycros and such, I don't see why it makes a functional difference when trying to downshift rev match.

    What I want to know is not why double clutching works. I'm asking why rev matching with a single clutch push doesn't.

  7. #36
    Registered User Micah's Avatar
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    And knowing is half the battle......

    Maybe this will help him understand it.

    In a parking lot or a long dead road - get the car to about 35mph in 2nd gear. Put the clutch in and wait for the revs to drop by about 1000rpms before shifting into 3rd. That should be about right for a rev matched shift from 2nd to 3rd.

    Now do the same thing, only this time, put the clutch in, take it out of gear (neutral) and let the clutch out. So you are now rolling along at about 35mph or slightly less, and the revs are falling. Let them fall way down to idle. Now give the throttle a decent poke so that the revs jump back up to where they need to be to enter 3rd smoothly. Then push in the clutch and put it in 3rd. If you do this correctly, the shift lever should go into 3rd with an eerie smoothness. Get good enough at it and you might even want to try just putting it into gear without using the clutch at all.

    That's the difference between a rev-matched shift, and a double-clutched shift. When you double clutch, you are making life very easy for your synchros since you are matching your engine speed with the rest of the driveline. But as others have pointed out in earlier posts in this thread - your car has a modern transmission and does not require that you do this.

    Does it benefit in any way to do this? Sure, provided you can do it properly - it's very very very easy on the driveline. You aren't shocking anything with rotational speeds (and thus loads) which need to be matched. However, if you do this wrong - you're gonna hear an angry symphony of metal as things meet in nasty ways.

    Choose wisely. Don't let the slightly more involving or complicated procedure scare you off, just be calm and relaxed while learning this. Go at a relaxed pace and think about what you are doing. Do it enough and it will become habit, I suppose.

    YouTube - Double Clutching

    Watch that to see it slow

    To see it a little faster watch this video. He first does it between 8 and 10 seconds in this video.

    YouTube - Double Clutch Downshifts
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  8. #37
    Registered User kempobmx1's Avatar
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    K. Thanks for the video link. That gives me a good idea of how it can be done at it's best. I'm clear on double clutching now.

    My other question was what the up and down pipe do for you. I assume the up pipe is simply a larger diameter pipe that allows for a more open flow towards the turbo. I would then assume that the downpipe is also just a larger diameter pipe, which reduces back pressure. I would imagine that, based on the downpipe's placement, it might also allow for faster spooling of the turbo, due to better flow through it.

  9. #38
    Registered User Micah's Avatar
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    An engine is an air pump. The more air it moves, the more power it can make. The stock exhaust system is restrictive. The stock uppipe in 2002-2005 has a pre-cat in it. This is bad for two reasons: one - it's restricting air flow to the turbo, and two - the cat can eventually start to break up and send damaging little pieces into the turbo. Later year WRX's (and all STI's) do not have the pre-cat. The stock downpipe is also quite restrictive so it's commonly replaced.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  10. #39
    Registered User kempobmx1's Avatar
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    So with the up pipe you're essentially removing the pre-cat. Can I still pass inspection without it?

  11. #40
    Registered User Micah's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    So with the up pipe you're essentially removing the pre-cat. Can I still pass inspection without it?
    Yes I think so. You can take a 2.2k ohm 1/2 watt resistor and put it where the O2 sensor plugged in. That should prevent a CEL.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  12. #41
    Registered User kempobmx1's Avatar
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    Since I'm by no means qualified to do that and I don't think my dealership's shop is either, would it suffice to just get the downpipe and skip on the up? Also I'm seeing a lot of stuff regarding cat-backs. I assume that's a wider pipe all the way from the last cat to the muffler? I understand that also would qualify as stage 2.

  13. #42
    Registered User Micah's Avatar
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    Extreme heat is what will kill the pre-cat. If you replace the downpipe you will get a performance increase, but you will likely also be driving the car harder. This will increase your chances of turbo failure when and if the pre-cat starts to break up.

    Find a shop to do the work. Your dealership mechanics/service dept can replace the uppipe but they may not want to. Ask them if they are open to modifications.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  14. #43
    Registered User kempobmx1's Avatar
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    Getting them to do it isn't the problem. The GTR tech at my dealership can do all that and he'll take money under the table if I want mods. My issue is this. I don't know that he'll know how to put that resistor in, nor would I even know where to get one. Without the resistor, the CEL would be on, in which case I can't pass inspection.

    Next time I see him, I need to ask the GTR tech what he's capable of doing.

  15. #44
    Registered User Micah's Avatar
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    Quote Originally Posted by kempobmx1 View Post
    Getting them to do it isn't the problem. The GTR tech at my dealership can do all that and he'll take money under the table if I want mods. My issue is this. I don't know that he'll know how to put that resistor in, nor would I even know where to get one. Without the resistor, the CEL would be on, in which case I can't pass inspection.

    Next time I see him, I need to ask the GTR tech what he's capable of doing.
    2.2K ohm 1/2W 5% Carbon Film Resistor pk/5 - RadioShack.com

    bend it into a U and put it into where the sensor plugged in
    Start using the search function. This is not new info.
    Last edited by Micah; 09-26-2009 at 05:13 PM.
    Torch Red 2002 Chevrolet Corvette Z06 46k mi.
    Black 2002 Subaru Impreza WRX 6-speed 94k mi. my mod list
    10/08/2006 - 14.089@103.01 (5-speed with well worn clutch, no launch)
    "Six stars gleaming, five speeds breaking, four tires chirping, three differentials working, two liters screaming, one turbo boosting... it's what makes a Subaru all-wheel-drive, all we'll drive."
    for Bugeye owners my BOV thread Service Manuals

  16. #45
    Registered User kempobmx1's Avatar
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    Will do. Thanks for the easy info.

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