1. Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

Custom exhaust question

Discussion in 'XJ Modifications' started by Ken w, Jul 7, 2020.

  1. Ken w

    Ken w New Member

    Messages:
    18
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    New York
    Ok so i have a buddy who is willing to build me a set of exhaust pipes for my 82 xj750. my head pipes are good still it’s everything else that’s shot, he’s suggesting we take my head pipes and build them into 2-1 sets for the bike, anybody have any pros and cons of this?
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    Ken w likes this.
  3. Ken w

    Ken w New Member

    Messages:
    18
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    New York
  4. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    you would have to weld a pipe across the gap. it is part of stock muffler setup.

    is it needed? its not on aftermarket exuasts. but yamaha put it there for a reason.
     
  5. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    Did Yamaha put it there for scavenging? Interesting what you are stating?
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    They did. It helps to meet emissions, and to improve power/ fuel mileage.
     
  7. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    So how efficient are systems without the cross pipe k-moe? So when one cylinder is on valve overlap another one will scavange the leftover exhaust gas in that cylinder with negative pressure in the pipe and help fill that cylinder on it's intake stroke?
     
    Last edited: Jul 8, 2020
    Hell Raiser likes this.
  8. Hell Raiser

    Hell Raiser New Member

    Messages:
    25
    Likes Received:
    10
    Trophy Points:
    3
    Location:
    Phoenix AZ

    For the most part, your pretty spot on with that summary. 1583837623253.jpg
    This is my first exhaust I designed for my bike, pretty along the same lines from what you said, I based it off the original head pipes and went from there. Are you planning to jet the carbs?? If I could make a suggestion, I would get a jet kit. I noticed after I did this exhaust it ran lean. But had an insane low end pull.
     
    k-moe and Franz like this.
  9. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    At the moment l have a Motad 4 into 1, and l am currently rebuilding my engine. Might have a go at making a system like yours in future. I will start with the Yamaha header pipes too.
     
  10. Hell Raiser

    Hell Raiser New Member

    Messages:
    25
    Likes Received:
    10
    Trophy Points:
    3
    Location:
    Phoenix AZ
    Too cool, you posting build pics as you go? I just updated my thread * PROJECT HELL RAISER* with a good selection of pics I've taken since May.
     
    Franz likes this.
  11. Franz

    Franz Well-Known Member

    Messages:
    3,646
    Likes Received:
    1,037
    Trophy Points:
    113
    Location:
    Scotland UK.
    I am going to post pictures of the engine rebuild soon.
     
    Hell Raiser likes this.
  12. Minimutly

    Minimutly Well-Known Member

    Messages:
    1,746
    Likes Received:
    748
    Trophy Points:
    113
    Location:
    West Wales, uk
    Exhaust design - whole books have been written about it. Nothing is simple here - firing order has a bearing on the need for a crossover, someone mentioned pressure waves? Well scavenging is about using a negative pressure wave being reflected back up the pipe to an open exh valve on a suitable cylinder - hence the need for a crossover in some cases. 4 into 2 into 1 is the standard fittment for car engines, but the paired cylinders are 1 and 4, it makes sense since they are equally spaced apart in firing time. But bikes don't generally have room for crossing 1 to 4. So the best compromise is the link or crossover pipe.
    Then you have a 4 into 1 - no crossover as such. But that negative wave will still be coming back, and then what happens to it?
    Damnit, I can't remember why this type generally gives less torque but more top end power?? Will have to get the books out...
    Anyway, if you change or remake your exhaust I would recommend copying the original, Yamaha knew all about tuning pressure waves and such, and unless you're re-tuning the rest of the engine it would surprise me if you could beat their design. If you raised compressions, retimed the cams, fitted bigger flat slides, gas flowed the head, then a 4 into 1 would likely net you more top end, but that's no more than a guess based on experience and some playing garound with motion pro software.
     
    Hell Raiser, k-moe and Franz like this.
  13. Simmy

    Simmy Well-Known Member

    Messages:
    2,261
    Likes Received:
    1,126
    Trophy Points:
    113
    Location:
    Waterloo Ontario Canada
    Thanks @Minimutly what you described easily clarifies this. Yamaha describes it below, I took this from the Turbo manual.
    I had a 4-1 Supertrapp mounted on my 911X sidecar combo but as you stated, room under the motor is not abundant.
    When I went to 16" wheels I smashed the pipe on a speed bump.
    My solution was to make my own 4-1 using XJ750 head pipes feeding into the Turbo exhaust chamber.
    It has 1&4 and 2&3 joining but still keeps a low profile.
    I made up an outlet pipe which bolts to the Turbo exhaust chamber and slips into the Supertrapp can.
    These Turbo exhaust chambers are easily found on E-bay.

    exhaust chamber.JPG
     
    Franz likes this.
  14. Simmy

    Simmy Well-Known Member

    Messages:
    2,261
    Likes Received:
    1,126
    Trophy Points:
    113
    Location:
    Waterloo Ontario Canada
    sorry one other important factor just came to me.
    I had to remove the left pedestal for the centre-stand.
    The Turbo centre-stand pedestals are more widely spaced than the other XJ's.
    You will loose the centre-stand if you go this route.
    One nice feature is that it still utilizes the rubber isolation mount on the bottom of the motor.
     
    k-moe likes this.

Share This Page