Topic: header options, building my own...

[oddballmotorsports]

so got this bastadardized 3 wheeler with a 81 cb650 in it.  one of the many things that's wrong with the design is the exhaust.  I am going to build a 4-1 header using whats left of the stock exhaust pipe.  anywho whats a good final diameter for a single exhaust pipe?  the motor will live mostly in the mid to high rpm range while riding.  also I might want to pair companion cylinders (4-1 and 3-2?)  for scavenging.  can that be done with a 4 into 1 header?  or would it work better 4-2-1  I might have room to do that.  Thanks folks!

[calj737]

Pairing of the cylinders on the same coil doesn't seem to me to be a scavenging benefit. Pairing on alternate fires does. But you are essentially describing 2 2:1 pipe sets, not a 4:1. Due to space and length limitations, getting 1/4 to join far enough before a collector would be pretty tricky given their width, the height of the frame-to-pavement, and the length of the motor. You'd need to wind them pretty hard.

I have seen 2:1 systems that run into single outlets down either side, paired with opposing cylinders. I have no data to suggest either is better or worse for scavenging. But coating the interior of the pipe will help insulate the exhaust gas from the pipe and make the pipe scavenge more efficiently.

CycleX has a pipe set for a 750 that is paired so that might be a worthwhile option for a template. http://www.cyclexchange.net/Performance%20Pipes%20Page.htm

[calj737]

Here's another option:
http://forums.sohc4.net/index.php/topic,161974.msg1860964/topicseen.html#new

Cheap enough to buy and alter to fit your head perhaps?

[oddballmotorsports]

I want to avoid running the exhaust under the bottom,  Its already got almost no ground clearance. because thats the way its run now.  if I have no other option, i might run "squashed" oval pipe underneath, after I finish retweaking the frame / forks etc. but would like to avoid that all together. I do have plenty of room between the motor and front wheel for long primaries to loop around before they meet the collector and then at best guesstimate, run about 1.5" down one side between the frame and the motor on the stator side.  hence the question of what diameter pipe is good enough for a single.  here's some pictures for ideas...

no ground clearance


primary space!


thinking maybe looping the primary's around the oil filter housing or something like that..  and then doing the pipe

[oddballmotorsports]

Forgot to add. I have to measure the exhaust ports but I thought about using a scrounged header from a little car like a civic or something,  but I have no idea what size primaries to use..  anyone have any thoughts on that?  theres little to no cheap motorcycle exhausts on craigslist, but lots of car parts..

[bill440cars]

      Whoa, now that has got to be "One Powerful 3 Wheeler"!!     When you get this one, squared away, I'd like to hear how it goes. My Dad picked up on a .79 CB750K, with an ATV 3 Wheeler Swing Arm setup attached on the rear of it. I ended up with it and at first, I was going to pull the ATV rear and Put the 750 Part of it away, for possible spares for my '80 CB750K. But, situation came up, that I moved out of state and when it came time, to move completely out of the home I was selling, I had help from Good friends and there was miscommunication and I lost that one. You see, there were some things going to salvage and before I realized it, They thought I was tossing that one and loaded it to go to salvage, along with an '80 CB650 Parts bike. Anyway, my mistake. I should have made it more clear and perhaps written down, what I wanted to keep. Too late now though.    But, those Friends helped me Tremendously.     

[oddballmotorsports]

It will be fun that's for sure.  I have only test ridden it with 3 flat tires for about 5 minutes to make sure it ran / rode before I bought it.  its a cobbled mess.. (I payed $400 for it lol) I'm setting out to make it (hopefully) ride well. 

back on my questions of exhaust,  I finally got around to measuring the primaries from my quickie measure, they look like they're 1 7/16ths.  most civics / toyotas etc etc have a 1.5 collector diameter,  so its close. If I were to modify a car header to work by shrinking the primaries down at the exhaust port (or ran a spacer), and ran 1.5 primaries in a 4 into 1 setup,  what would that get me?  the biggest restriction no doubt is the exhaust valve and port,  so, would that be advisable?    I'm not hellbent on using a car header,  their just cheap and prevalent.  also as another option,  I can have my exhaust guy bend up 1.5 tubing in any way I see fit,  then i can just use an off the shelf collector into im guessing 2" pipe.  but for space reasons,  1.5 would be better.