DRZ400S stock exhaust mod

Discussion in 'The Garage' started by dirtridr5115, Apr 15, 2018 at 6:46 PM.

  1. dirtridr5115

    dirtridr5115 dirtridr5115

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    I have been doing some looking around online (and on here) to see what is out there for improvements to the stock exhaust to compliment the jd jet kit and the 3x3 mod... havent been a able to find anything substantial so i will just ask on here. What can be done to the exhausts to improve the performance of the bike?

    I found an article on youtube:

    This article talks about the guy wanting to make his bike sound better, which means nothing. I just want to know if anyone else has done this and what does this do for performance?
    #1
  2. oldmanb777

    oldmanb777 Just say NO to socialism!

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    Physiologically makes it more powerful by making it louder. But in reality probably does nothing. You would need the cams, compression, carb of the "E" to get any more out of it. And then the bigger Generator, brakes and everything else will still make it an "S". after the JD kit and 3x3, it breathes pretty well. Probably as well as its going to.
    #2
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  3. shovelstrokeed

    shovelstrokeed Long timer

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    You will find all sorts of articles on exhaust modification. The factory also did a bunch of engineering on the exhaust system of your bike. It has been ever thus. Do a little more research and look at older exhaust systems and muffler designs. There are myriad solutions to the same old problems. The problem being that none is optimum for a given application. Absolute top acceleration can result in an exhaust system that sucks in the mid range and will barely tolerate idle RPM. Good mid range power and a torque curve with no big holes in it requires different application of the basic principles of exhaust design than just drilling a couple of holes in the baffle.
    You are left with a dilemma. What are you looking to improve? HP? Torque? Drivability? Sound? Weight? Economy?
    Each of these considerations come quickly to the front when you start messing with the factory exhaust. Almost none of them will improve without sacrifice to other factors.
    If I sound like I'm advocating for the factory exhaust, I am. Unless you are building some monster street bike and don't care about any other factor, leave the exhaust alone. Concentrate on tuning. Get the jetting right with the standard components and leave the exhaust as one of the last things you modify. You already have a simple single cylinder engine of relatively small displacement. You want more performance? Go to a bigger motor. Then you will satisfy most of your needs.
    The answer to your question lies in there somewhere. I've been at this shit for 60 of my 75 years and have yet to come up with a satisfactory solution.
    #3
  4. oldmanb777

    oldmanb777 Just say NO to socialism!

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    Extremely well said!!!:nod Amazing how many people don't understand this FACT! And its so basic. :thumb
    #4
  5. shovelstrokeed

    shovelstrokeed Long timer

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    Basic it may be, but so often ignored or simplified to the extent that it may as well be ignored.
    At its root, exhaust system design is about air flow. At some level, an increase in volumetric efficiency at the intake side must be matched by a similar increase at the exhaust side but by how much and at what RPM range do we select exhaust components to match improvements to flow.
    Typical parameters for a factory exhaust system are, in order of importance:
    1. Fitment to the motorcycle in question.
    2. Compliance with noise regulations and, in the case of off road vehicles, fire danger via sparks from the exhaust.
    3. A broad range of power given the implied or intended usage of the bike.
    4. Cost of manufacture of the components of the system.

    #4 could easily be swapped for #1 as the motorcycle would need to be price competitive as well in order to sell.

    Now, certainly, an MX bike would have different requirements for #3 than a generalized street bike such as the DRZ but the principles are the same. Ditto a street bike when compared to a MotoGP bike although you might find a MotoGP bike is surprisingly easy to ride on the street as one of the requirements in road racing is a broad range of power. The absolute power is where the GP bike differs but that is just a matter of how far and how fast the throttle is twisted.

    I would suggest to the OP that a slip on muffler made of TI might be the best path to performance, not so much about the exhaust flow but the savings in weight might yield a measurable gain. Of course, some tuning may be needed, even with the slip on, but it shouldn't require much beyond some basics. Blindly changing the jetting to some arbitrary sizes specified in a jetting kit might be a start but probably is no where near ideal at this point. It all ties together, compression ratio, ignition timing, cam timing, cylinder head design and port shape and size. They are all related. Now add gearing and a quick throttle to the mix and have fun. Check back in a year or so and let us know how you made out.
    #5
  6. ohgood

    ohgood Just givver tha berries !!!

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    the 3x3 and jets make the biggest difference

    everything exhaust related is just noise
    #6
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  7. dirtridr5115

    dirtridr5115 dirtridr5115

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    Thanks for the input! I already had done the jd kit and the 3x3 and i could defiantly tell there was a major improvement in throttle response. Just wasn't sure what more could be done without going loud. Was also looking for a lighter battery, but I just got Giant Loop Coyote so losing weight and gaining it right back...

    What other improvements can I make to help make it more of an "enduro" overnighter?
    #7
  8. ohgood

    ohgood Just givver tha berries !!!

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    get it sprung for your weight
    led headlight (longer battery life for setting up camp)
    good tires
    $4 trashcan windshield

    it's a really good bike for camping, after you take care the known issues the factory still isn't addressing
    #8
  9. dirtridr5115

    dirtridr5115 dirtridr5115

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    1) Thank you for the response
    2) Looking for improvement in Torque (while minimizing sound); I've dropped a tooth in the front gear and added 1 in the rear as well.... I also have the clarke 3.9 so while economy is nice to keep i can afford to lose some eco if necessary without worrying about running empty like i used to do with the stock tank between towns.
    I love my stock exhaust, the bike is awesome after I did the 3x3 and just looking to see what else I can do to make it just that much better.

    There's a lot of talk about how heavy the stock exhaust is as well. Muffler repacking maybe would help this?

    I'm only 135, maybe 145 with gear so I'm not the biggest burliest guy out there. I like the size of the 400 because of how much of a dirtbike it feels.

    Thanks for the input shovelstrokeed, I will keep tuning and fine tuning my jetting and mixure.
    #9
  10. dirtridr5115

    dirtridr5115 dirtridr5115

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    I just started looking into the windshields the other day. My dad and uncle ride and are looking for doing some weekend trips this summer so I was looking at the windshield and also the LED (or HiD) headlight conversions. Maybe some add-on lights outside the stock lighting.. so many options
    #10
  11. dirtridr5115

    dirtridr5115 dirtridr5115

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    I need to go back over the bike with my gear loaded up to setting the suspension right. I havent done much with this since I got the bike years ago (shame on me). So step 1, take it back to stock then adjust. adjust. adjust... without getting all my actual camping gear out of storage and packed for weight what is the "normal" weight for a weekend of camping gear (I know stupid question)... my guess is set it for me plus 50-60 (gear weight plus gear)????
    #11
  12. ohgood

    ohgood Just givver tha berries !!!

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    depends on your camping gear. one guy is 35 the other 65
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  13. Yinzer Moto

    Yinzer Moto aka: trailer Rails

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    I weighed my camping setup recently. 16 pounds. The kitchen can be eliminated and just eat before/after camp but that adds to the daily costs. This is everything I bring along for a weekend or month long trip.

    Attached Files:

    #13
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  14. oldmanb777

    oldmanb777 Just say NO to socialism!

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    Most of the throttle response comes from the needle of the JD kit. If you compare the stock needle to the JD Needle you'll see it. the stock one is smoothly tapered, the JD isn't. So when it comes off the jet, its instant fuel. Big help in throttle response on the CV carb.
    #14
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  15. shovelstrokeed

    shovelstrokeed Long timer

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    Want more torque? I can understand that but really, I suspect you want snappier throttle response and a little more power. You can get that, but it isn't gonna come with just an exhaust modification, which really only can help high RPM performance. You made a good first step in increasing torque output to the rear wheel by changing the gearing.
    The next steps would be more compression and a cam with different lift characteristics. At the base end of this, a cam designed for better torque output in the low to mid range will have similar duration to stock but more and faster lift. This puts higher stress and demands on the valve springs and may introduce clearance problems with valve guides and valve to piston clearances as well. Best installed by someone with some expertise in these matters and the ability to properly measure clearances and cam timing.
    It is possible to gain a small amount by slightly advancing the cam timing on your stock cams but there are still valve to piston clearance issues to resolve. There are offset bushings available to do this job. If you engine has dual overhead cams, you can change lobe centers to achieve some of the same effects. A slight sacrifice in ultimate power for a bit more torque in the mid range where most of your riding will be done.
    There is no free lunch in this business. Some changes will cost in parts, some in reliability and some in fuel economy. The old saying is still true, speed costs money, how fast can you afford to go?
    #15
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  16. aldend123

    aldend123 Long timer

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    You want more low end on a 400 thumper, you're 135lb, and you've geared down? :hmmmmm

    Maybe you really love instant power. But I wonder if something else is wrong. Carb tuning resulting in poor initial throttle response? Habit of lugging to high a gear? Do you ride with 1 finger on the clutch? Because you should. Zap the clutch in the right gear and it should give a good pull.
    #16
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  17. dirtridr5115

    dirtridr5115 dirtridr5115

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    I think carb tuning is pretty good cause I've checked the plug and it looks great. No i dont ride with finger on the clutch. I ride as a communter to work and its great for that and road tripping, just looking for making it a good enduro racer for on the weekends without dumping crazy money into it.. maybe a little lighter weight here and there would help.. suspension tuning would be great help as I havent done much with it yet.

    I will have to spend time tweaking that.
    #17
  18. dirtridr5115

    dirtridr5115 dirtridr5115

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    Thanks for the info!! I have a personal cook set (mess kit) i used when was a boy scout camping and a single burner camp stove. I have an Eno hammock (double), do you have a rain fly for the hammock in the picture somewhere?
    #18
  19. Yinzer Moto

    Yinzer Moto aka: trailer Rails

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    Yea, the rain fly is on the bottom left.
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  20. Fixnfly

    Fixnfly Been here awhile

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    The best mod I could find for my stock exhaust is coating by Jet Hot. 12-17-15 065.jpg
    #20
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