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JR Hammer
XS650 enthusiast
eh?? not understanding the question... I took the stock headers and buzzed the mufflers off just downstream of the middle collars and mounting bracket with a die grinder and a cutoff wheel. If you leave the inner pipe in place they end about 3 or 4 inches behind my feet-- with pegs in stock configuration. The inner pipe at that point is only about 1 inch diameter.
hotrdd
XS650 Junkie
So this raises an interesting question. I think we all agree that the compression is important but how do you determine what it should be? Does anyone have some back pressure numbers? Would we be able to weld on a fitting and use a compression tester to determine internal back pressure? I have a set of open straight pipes and I’m wondering if maybe they are to open.
bloodthirstysystem
XS650 Addict
i dont see how the length of the pipes will change your compression.. your pipes can be whatever length you want, it will need to be jetted correctly. it will change your MPG, horsepower and performance
Capt_Zoom
Raider Rider/xs newbie
Mike at 650 central suggested going up a size on each of the jets if cutting them off where JR Hammer described. That's what I'm doing.
Going super short, cutting off right by the downtubes could cause some valve problems though.
Going super short, cutting off right by the downtubes could cause some valve problems though.
Might find some help in this thread http://www.xs650.com/forum/showthread.php?t=4719
I've often asked the same question.
I've often asked the same question.
awoz87
XS650 Enthusiast
that thread has a good explanation on back pressure and why it doesnt really matter. proper jetting is going to be the most important thing.
i would make them whatever length you think looks good for your build and then mess around with jetting from there.
i would make them whatever length you think looks good for your build and then mess around with jetting from there.
JR Hammer
XS650 enthusiast
Yes I left them where they are because you get that little mounting tab to fasten them down to the frame. Generally speaking it is not a good idea to have your exhaust suspended solely from the flanges. Vibration stresses over time can cause the exhaust studs to become brittle, crack, and break off leading to severe exhaust leaks (like when you are riding on the interstate and your header pipe falls off and gets run over by a f*#%ing semi-truck) and/or leaving you with studs busted off flush with the head... where you'll need to drill/tap and ez-out (or not-so easy EZ-out) I dont have a decent camera or I'd take a pic right now, just have my stupid smart phone and haven't figured out how to add photo from it yet...
basically your stock pipes are a pipe inside a pipe. the inner one is smaller than you'd think. They come down to a tapered collar where the mufflers are attached. The header pipes go about 6 inches past the tapered collar inside the mufflers and then stop-- the body of the muffler serves as a sort of am expansion chamber and a resonator with a baffle at the outlet end. They are all mechanical, there is no packing. The skin of the mufflers is like .064" thick and if you cut with your die-grinder wheel about a half inch downstream of that tapered collar you can remove the entire muffler and leave just the head pipes... let me see if I can get a pic up...
basically your stock pipes are a pipe inside a pipe. the inner one is smaller than you'd think. They come down to a tapered collar where the mufflers are attached. The header pipes go about 6 inches past the tapered collar inside the mufflers and then stop-- the body of the muffler serves as a sort of am expansion chamber and a resonator with a baffle at the outlet end. They are all mechanical, there is no packing. The skin of the mufflers is like .064" thick and if you cut with your die-grinder wheel about a half inch downstream of that tapered collar you can remove the entire muffler and leave just the head pipes... let me see if I can get a pic up...
JR Hammer
XS650 enthusiast
sorry it's a little bit blurry, the lens on my phone is probably dirty and I forgot to clean it... plus these pics are taking forever to upload from my stupid smartphone
okay, and here's another view so you can see the tapered collar thingy I'm talking about:
I left the rear exhaust bracket on there for now because without it the middle-stand will flip all the way up against the rear brake push-rod and sit in front of the left pipe which gives a partial obstruction and makes the exhaust note sound a LOT LOUDER in my ear while riding. So with the bracket on there the middle-stand rests against the bracket and obstructs the pipe outlet a little less.
I find with this setup that the low-end torque is somewhat flat and you have to re-tune the mix screws to keep the engine from popping. Ideally you should put a small flat washer under the needle-clip in each carb-- in essence "raising the needle a notch or two" or upsize the main jet to compensate. For me it's running good with minor mix adjustment (only seldom backfires and idle does not hang up very much) but could be better because still it is a little bit lean without the adjustment... these "emission" carbs dont have notches in the needles like a good mikuni should but you can achieve richening needle adjustments by shimming up the needle with small plastic flat washers under the clip like I said...
The length of a header pipe is determined by engine size and the diameter pf the pipe.
A head pipe of say 36 inches and 1 1/8 inside diameter will give a max power at say 6500 rpms.
If you make the pipe shorter the max power goes up the rpm range. At say 30 inches long the max is 8000 rpms. Not vey streetable.
If you use a larger inside diameter pipe the power goes up the rpm range.
A good header pipe for a 650 to 750 cc XS engine is 1.5 inside dia, about 32-36 inches long.
This gives you a wide power band that works well on the street. It can be a bit hard to tune the carbs to.
Adding a free flowing muffler can improve the lower rpm responce. And it will help quiet the exhaust note so your hearing isn't damaged. And will save a lot on noisy exhaust tickets.
Leo
A head pipe of say 36 inches and 1 1/8 inside diameter will give a max power at say 6500 rpms.
If you make the pipe shorter the max power goes up the rpm range. At say 30 inches long the max is 8000 rpms. Not vey streetable.
If you use a larger inside diameter pipe the power goes up the rpm range.
A good header pipe for a 650 to 750 cc XS engine is 1.5 inside dia, about 32-36 inches long.
This gives you a wide power band that works well on the street. It can be a bit hard to tune the carbs to.
Adding a free flowing muffler can improve the lower rpm responce. And it will help quiet the exhaust note so your hearing isn't damaged. And will save a lot on noisy exhaust tickets.
Leo
Blowtorch
XS650 Member
I have made many different bikes with strait pipes and if you plan on ridding it more then a few miles make sure they end behind your ears or kick the ends away from the bike.
I can't HEAR you................... Mufflers, making engines run BETTER since 1880.
Blowtorch
XS650 Member
Loud pipes save lives! And if you know how to tune a motor right it will run faster and better with out mufflers. Why do you think dragsters and other racing platforms don't use them..... my 2 cents.
Tomterrific
XS650 Junkie
Blow,
Dragsters run in a very narrow high rpm range. The engines run like crap at rpms below that range.
The best book you can read is "Scientific Design of Intake and Exhaust Systems" by Philip Smith. Ask for it at your library and they will get it for you through inter library loan.
Tom Graham
Dragsters run in a very narrow high rpm range. The engines run like crap at rpms below that range.
The best book you can read is "Scientific Design of Intake and Exhaust Systems" by Philip Smith. Ask for it at your library and they will get it for you through inter library loan.
Tom Graham
69er
XS650 Enthusiast
how long you want them???.......................that is the answer!!....who cares what anyone else likes or thinks..you could run them past your rear wheel if you wanted.
you can always baffle them or use torque cones.
I am running 1.75 on a bike i built for my kid, probably a foot pass the foot pegs....I have never ran pipes that big and i am surprised how quite they are for straight pipes...I 'll report later on performance, after i ride it a few times..
Tomterrific
XS650 Junkie
I rode on a Mods and Rockers get together/bike show yesterday. I took my SR500 which I originally thought was loud but now doesn't seem that bad. The guy behind me said all he could hear was my bike, not the 50 choppers in front of me with straight pipes. (???) I think it's the high compression piston and maybe the Supertrapp is a little loud. If you look at the cap on the end it has a big hole and it says "For Competition Use Only". Shhhh! ;^)
I think it's a good plan to make the pipes long and if you want them big, over 1 1/2" diameter, you should step them up from smaller dia. right at first.
Tom
I think it's a good plan to make the pipes long and if you want them big, over 1 1/2" diameter, you should step them up from smaller dia. right at first.
Tom
I thought this http://downloads.650performance.com/XS650_750_engine_modiffication_guide_sample.pdf
Came as close as anything I have seen to answering your question with enough depth to be useful but not so deep as to make your eyes bleed! Good luck!
Came as close as anything I have seen to answering your question with enough depth to be useful but not so deep as to make your eyes bleed! Good luck!
ProSimex
XS650 Addict
I wouldnt sacrifice performance for the sake of having "straight pipes" Ive got 2 reverse cone mufflers on my 74 and it loves em. As far as being quiet is concerned my buddy could hear me downshift to take the corner 3km from work! Also loud pipes dont save lives, no one in their cage is gonna know where you are unless your right in front of em. You think that dipshit turning left infront of you while listening to ..... whatever it is the kids are listening to these days, can hear you? not unless you pipes are pushing sound forward.
