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changing exhausts on 1985 xj700 maxim help!!!!!!!!

Discussion in 'XJ Modifications' started by izhakiori, Apr 2, 2013.

  1. izhakiori

    izhakiori Member

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    hey so when i bought my bike the exhausts where plain nasty holes every where rust and the thing was clogged they are completely useless. it actually stopped me from starting my bike since they were so clogged. i couldnt find any replacement for them and dont wanna spend hundreds and replacements.
    i need some ideas please please please.

    i was thinking maybe to remove the huge peace that converts it from 4 into 2 and making it simpler with 2 different pipes making it 4 into 2 and then having a muffler under the bike itself not out the sides. and i wanted to know if i can just take any muffler and slap it on it without any engine or tuning problems like lets say take a muffler from an old cbr or r6 or something and put them on can anybody please help me out with some ideas and visual ideas are even better thank you in advance for your time and help
     
  2. SLKid

    SLKid Active Member

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    Ebay exhausts for the XJ700
    If its not stock, you will have to rejet and retune.
    Youre going to have to clean and tune anyway.
    Just easier with the stocker
    -Chris
     
  3. xHondaHack

    xHondaHack Active Member Premium Member

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    Izhakiori,

    Just sent you a PM on my exhaust setup you inquired about.

    Tony
     
  4. izhakiori

    izhakiori Member

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    thanks to both of you but my question now is can i take any random mufflers and put them on or it wont work like that
    for exampole i was thinking maybe getting new cone mufflers from here http://www.coneeng.com/motorcycle_components.html thought they look cool would it be any problem especially that u wanna remove the original collector and make a simpler looking one
     
  5. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    The kid answered the question right there fella ;)

    Obviously it's going to be pushing the boundaries a bit if you were to fit, say, Italjet 50cc exhausts but within reason any muffler/exhaust setup will work. BUT you will (to a greater or lesser extent) need to re-jet to avoid running lean & melting pistons or rich & washing your bores...
     
  6. quebecois59

    quebecois59 Well-Known Member

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    I've owned a '85 Maxim-X that had slash-cut aftermarket mufflers when I bought it.

    [​IMG]

    I ended up changing for another type of mufflers I bought for XS650 use, but I'd say any decent mufflers would do the trick, as long as as they don't interfere with the rear axle for maintenance.

    [​IMG]

    These mufflers fitted because the collector box exits were modified by PO to change the upward slope to a more horizontal profile.

    I would strongly recommend that you leave the 4-in-2 collector though (or build one of your own that would do the same job) otherwise you will most likely have all kinds of problems making it run properly. These bikes need some back pressure and exhaust gases sharing provided by the collector box.
     
  7. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    That's a myth I'm afraid, no engine needs back pressure as the goal of the exhaust is to vent gases as efficiently as possible. 2 strokes don't need "back pressure" as such either believe it or not, just (to woefully over simplify it) a couple of timed pressure waves, one to suck the exhaust out & another to push any escaped fuel/air mixture back in.

    If we had back pressure, think what would happen. The ambient pressure inside the cylinder would be equal to the pressure inside the exhaust when the valve closed, then as the inlet valve opened this pressure would be higher than the atmospheric pressure within the carbs/airbox & would force a small amount of residual exhaust gases back through the inlet before the induction stroke drew it back in along with a reduced amount of fuel/air hence we would have truly awful & inefficient performance unless we added a turbocharger to add, let's call it "fore pressure", that equalled or exceeded the back pressure.

    Obviously it's a lot more complicated than this & I don't know enough about timed (positive & negative) pressure waves & exhaust scavenging to comment further, but on a basic level back pressure is not needed.
     
  8. quebecois59

    quebecois59 Well-Known Member

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    That's a myth I'm afraid, no engine needs back pressure as the goal of the exhaust is to vent gases as efficiently as possible.
    (snip)
    quote]

    You may be right about the back pressure, but it doesn't change the fact that the collector box slows down the exhaust flow and allows exhaust gases from cylinders 1-2 to mix with cylinders 3-4. People who removed the collector box and modified the exhaust system in a 4-into-2 without any cross-pipe reported poor performance.
     
  9. izhakiori

    izhakiori Member

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    thank you all for your help
     
  10. beanssoccer

    beanssoccer New Member

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    I am currently dealing with poor performance issues due to removing the collector pipe. I installed a Mac 4 into 2 exhaust. Now the bike idles well and has nice power under 4k rpms. After that it bogs down and there is absolutely no power. I couldn't get over 75 mph on the highway!
     
  11. quebecois59

    quebecois59 Well-Known Member

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    Sorry to hear that, I would have thought you'd avoid that mistake after the warning I wrote in my last message.

    It is important that your exhaust system allows gases sharing between pipes 1-2 and pipes 3-4 before they go in the mufflers. I don't know what kind of modification to your Mac system you will need to have your bike run properly. You will probably need to fit a cross pipe between left and right just before the mufflers.
     
  12. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    I don't understand that, there's no need at all for cylinders to "share" or "balance" exhaust gases in any way either. If there was this need, how would single cylinder engines ever run?

    All you do by removing the collector (say for a 4 into 4) is create 4 separate single cylinder engines but on one crank (which you had anyway save for the link pipe). This may create issues that were dealt with by way of collector as stock, if you just cut the pipes or run open headers, but that can be largely negated by correct "tuned length" of individual pipes... (again it's down to timed pressure waves that are out of my depth)

    I'd bet the guy above simply needs to rejet for the freer flowing exhaust he has fitted (main jets no longer able to supply enough fuel for the extra flow allowed)
     
  13. quebecois59

    quebecois59 Well-Known Member

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    Poor performance has been reported many, many times by XJ owners who installed 4-into-2 systems with no cross-pipe neither collector box. THe stumble will be attenuated by different jettings but will most likely not disappear. It has been tried before, I can tell you. I can't explain exactly why, but the collector box is an important part of the exhaust system for our XJs. I think it is related to the firing sequence.

    It would work better with a 4-into-4 system (like early Honda CB750).
     
  14. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    Right I think I understand now, :D the pulse from one of the cylinders in each exhaust pair causing a problem for it's "opposing" cylinder, where if all 4 were connected the pulses would be smoothed out? so yes maybe a link pipe between the left & right would be beneficial in this situation. Perhaps I should have thought about the way the 4-2 setup is configured more carefully :roll: (if that is the problem, making the collectors so that 1 & 4 share a silencer and 2 & 3 share the other one would have been a better design if they really didn't want a link pipe)

    I do think the main issue on beansoccer's bike is likely to be jetting though since it's "running out of steam" at 75mph & not pulling through it at all.

    Maybe a plug chop would tell us more, I certainly wouldn't want to risk riding that bike much further until a good (non-lean) chop was achieved so no risk of overheating...
     
  15. quebecois59

    quebecois59 Well-Known Member

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    That was exactly what I thought a few minutes ago. Could be better for the pulse but I try to imagine having 1-4 connected to the same muffler, and 2-3 to the other...would need a very weird set of downpipes. Putting a cross-pipe is way much easier.
     
  16. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    Not really if you kept stock header exits and made the 2 collectors from Y pieces, a wider/longer one for 1/4 and a smaller one for 2/3 with a U bend for clearance round the first one...

    Could maybe make it look quite good as a custom system (a bit like the fancy custom headers for performance cars, snaking round each other), but for production the link pipe or a true collector box like stock would be easier... That's a point, why *do* aftermarket 4-2's abandon the H-box anyhow I wonder? :?
     
  17. Krafty

    Krafty Member

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    back pressure/ the correct amount of restrction is required to all exhaust systems to ensure they perform as well as the should.

    easy example.

    car without muffler / tail pipe exhaust ending under the middle of the car will make LESS power than the same car with a stock muffler and tail pipe.

    same car with better flowing muffler and tailpipe will produce more power than factory if the intake side of the engine has been modified. otherwise it will be = to stock.

    2 stroke motocross bike with no silencer is not only super loud but also has less power than with one.
    2 strokes also require the expansion chamber to increase the volume of gasses exiting the engine while the restriction at the end of the chamber increases exhaust flow speed through the silencer.

    cars equipped with headers are engineered to produce the optimal amount of restriction with the minimal amount for exhaust required.

    you can question my logic if you want but i've been racing modifying and fixing 2 stroke motocross bikes for the last 18 years.
     
  18. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    Good theory, but technically flawed. Read into walter kaaden's work into 2T expansion chambers for the full story on what the different parts do, the car example isn't strictly true either.

    If the flow is improved (restriction removed) and the car is able to compensate (through either EFI or tuning the carb/altering timing) it will make more power, to a certain point. But tuned length and pipe bore comes into play also so shorter/fatter pipes could result in less power as you said. not by reducing pressure or velocity as such, but by messing up the controlled wave structure engineered by the manufacturer to best work with that engine.

    It boils down to-: Back pressure is NOT and never was needed to make an engine run better. What IS needed is a correctly timed pressure wave or waves to optimise exhaust removal & fuel/air mixture "stuffing" on valve overlap. It's a lot more involved than simple back pressure & as I say I don't know enough to form a definitive statement of exactly how it works, but that's the basic facts all the same ;)
     
  19. Krafty

    Krafty Member

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    " pressure wave or waves to optimise exhaust removal & fuel/air mixture "stuffing" on valve overlap." = proper back pressure.


    in some situations we are saying the same thing in different terms.

    the "Back Pressure" as I refer it as described in your post is basically ways of using restrictions to increase exhaust flow speed from other cylinders to help Draw the exhaust out of the newly opened exhaust valve.

    too big a pipe increases volume but reduces flow speed, too small a pipe reduces the volume and doesn't allow the exhaust to flow fast enough to help Draw the gasses out of the cylinder.

    "walter kaaden's work into 2T expansion chambers"

    has to do with the resonance or sound waves and their effect on the exhaust gasses and how well the flow and maintain back pressure. Very important in machines that rev extremely high.
    my description is 100% accurate, I just didn't get into details how exactly the gasses maintain pressure in the cylinder to avoid drawing too much fuel and air in through the Reeds and preventing a loss in horsepower by having too much fuel in the the bike to burn efficiently.
     
  20. 750E-II_29Rbloke

    750E-II_29Rbloke Active Member

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    "my description is 100% accurate, I just didn't get into details how exactly the gasses maintain pressure in the cylinder to avoid drawing too much fuel and air in through the Reeds and preventing a loss in horsepower by having too much fuel in the the bike to burn efficiently."

    I'm not going to argue my point forever and a day 'cause frankly I don't care enough lol, but drawing too much fuel/air mix is impossible (otherwise turbocharged vehicles would lose power on boost through too much fuel/air)

    What a 2t chamber aims for is to act as a resonant supercharger at a specific rpm range, by it's "stuffing" wave pushing back any mixture that escaped down the pipe during the first "suction" wave. This is why 2T engines with spannies have a narrower but more intense power band than a straight pipe or simple megaphone.

    I'm tired and CBA with this now so I guess you win :p , but plain and simple restrictions in exhausts reduce power, correctly tuned exhausts that get as much spent mixture out as possible (and in the case of 2T's stuff back the fuel/air that escaped during port overlap) increase power.
     

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