GStwin.com GS500 Message Forum

Anyone know anything about straight pipes?
I'm wondering why most sport bike exhausts are barrel-shaped and not straight through...

I've been toying with ideas regarding exhausts for a while now and I'm wondering other than backpressure and other issues, why not just mount straight piping with a few bends (to produce more pressure...) and have it come out under the bike or under the tail?

My bike is slowly becoming an innocent guinnea pig...  

Rolly

Interesting idea.   Other than legal considerations, I don't see why you can't use straight pipe.  My knowledge is limited in this area but from what I understand, the muffler is only there to muffle sound.  The pipe only exists to direct the exhaust gas to the muffler and prevent your front wheel from catching on fire.  :thumb:

The best exhaust system (for performance) would be no exhaust system.  Backpressure doesn't improve performance (as far as I know).  So I don't think you need those bends you were talking about.  The reason a bike might run crappy on less backpressure is that the fuel mixture might be too lean with a free flowing exhaust.  Solution ... add more fuel = more HP.  

To add to this ... if you're designing new pipes, you have to balance the flow and length of the two pipes so that when they come together at the joint (assuming you make a 2 into 1), the low pressure pulse of one pipe draws out the high pressure pulse of the other pipe.  This will increase the flow rate over dual pipes for example.

Sorry if you know all this already.  (and correct me if I'm wrong)

Rob

I think you have something when you talk about back pressure and fuel mixture. Try starting the bike without an exhaust system, like this propose straight pipe. I know on mine it won't start.

With no pipes you'll warp your heads due to every combustion resulting in a backfire.  Some back pressure is needed to keep the flash in the cyclinder and not in the exhaust.  Look at almost all high performance vehicles and you will see some sort of exhaust.

true, some engines will run with a straight pipe but lose a lot of power....i didn't start my bike when i had the muffler off because of the noise but i wouldn't run it without the muffler for 2 reasons....it would be too loud and the sound would be more like a harley then a sportbike

I have been toying with the idea of a straight pipe that is routed under the tail for a few weeks now. I have a design I like with damn near equal lengths, and enough bend that it will create some back pressure. I did the calculations in one of my engineering classes. Anyway, I have to wait and see when I get back to my bike in a montha nd a half. But the design is in the works.

straight pipes work, but (from my experience), they tend to sap some of your torque. for example, look at these little cars, where their owners put one of these "coffee can mufflers" on it. quite sim. to straight pipe. but they do nothing else. listen to how hard they have to run their engine to get it up to speed. you can get straight pipes to work, but probably will wand to tweak the mixture, and also be ready for it to be noisy, and quite possibly sound like an american twin. i used the drill and puch technique on my muffler, and the idle note souds like hd, until i open her up :dunno:

yeah, you can run straight pipes, but you need to do some homework on reseting mixture,spark timing, cam timing, your power band will more then likly narrow up abit. better off running a narrow Can on the pipe.

another idea, if you want to run it on the side, take a factory can,cut enough out, so you can pass the pipe thru it from end to end, then it'd be hard to tell the difference between it and a fact. system, uhhh, except for the noise level

QuoteBackpressure doesn't improve performance (as far as I know).

You must be unfamiliar with the Brotherhood of EXUP:


http://www.exupbrotherhood.org/frmlistinfo.html

http://www.tramontozzi.com/exup/missexup.html

WARNING:  Adult Content (i.e., click the 2nd link!!!)

I'm really basing my whole idea that it would work on cruiser pipes... you often see Harley's running straight pipes and from talking with folks running dragbiokes, straight pipes increase your torque... but reek havoc on your top end HP...

I might try it just to see if it can be done... my high mount pipe system worked out, but I was getting too much heat coming from it and I was paranoid I was slowly killing the engine with the thing, so I ditched it, but now I'd like to look at a system to run under the bike ala Buell... since space would be limited, I was thinking of using a pipe bender and bending enough length of pipe so I would actaully be running a longer pipe, just bent up...  maybe I'll put the system together and take it to a dyno and see what happens.  


Rolly

Harleys NEED to have straight pipes!! They simply don't run properly without them. (Triumphs too) They are such a dated design (Farm tractor).

The biggest difference is Harleys are long-stroke motors to begin with. The underbore combustion chamber is not designed for high flow, so the straight pipes help that out immensely.

Quote from: scratchHarleys NEED to have straight pipes!! They simply don't run properly without them. (Triumphs too) They are such a dated design (Farm tractor).

The biggest difference is Harleys are long-stroke motors to begin with. The underbore combustion chamber is not designed for high flow, so the straight pipes help that out immensely.

I was about to say why not try a megaphone pipe like a Bonneville has.  They look pretty darn cool and I bet it would sound good too :).  I think Staintune makes them for Triumphs.  It might take some creativity (read: rigging :lol:) but I bet they could work.  Don't know if this pic will work but its from the Staintune AU site

Gisser:

What am I supposed to be looking at on the Exup site?! (besides the girls .. BTW I vote for no. 4) :thumb:

Rob

Heh, No. 4 must've been the Haga my mama.

The point is that EXUP valves boost low end power by partially blocking exhaust flow (backpressure) at low RPM's.  EXUP is Yamaha but all the liter reps have their own version, I believe.

Check this out.  

(http://img16.photobucket.com/albums/v47/adamr/DSCN3109.jpg)

I'm actually running a megaphone exhaust right now - and it's VERY loud... looks a tad outta place, but I kinda like it...

I've removed the rear passanger pegs and I've had a bracket made that runs off of a couple mounting points on the bikes subframe, so mounting an exhaust wouldn't be a problem (the bracket I had made is actually adjustable, so I can use a variety of different exhausts).

My main interest in running a straight pipe was to either get the pipe completely under the bike (ala Buell...) or up through the swing arm (by the shock) and out throught the rear subframe.  I don't think a canister would fit in either of these locations.  


Rolly

Quote from: Adam RCheck this out.  

Thread jack!

What is up with those bars!?

Sorry for jackin' the thread, I just had to ask!

Check out this link ...

http://auto.howstuffworks.com/framed.htm?parent=question172.htm&url=http://www.nightrider.com/biketech/calc_exhaustlength.htm

this is something you DIY'ers might try and let us know how it works out.

I think you more or less need a straight pipe for this to be of any benefit.

Rob

If you want to know how loud straight pipes are, swing by my place and I'll fire the bike up.  I'm getting ready to fit oe pipes for my GS450(as soon as I get a chance to do it right), but I bought it a few months ago with straight pipes and turndowns on it, and I really don't like it.  If you want loud, it is a great way to got especiallly if you use the megaphone with it, but in the real world, I would rather hear the cars and (esp.)trucks around me.  

As far as the backpressure issue, you do need some in the real world, the pressure pulses from one cylinder will help to pull exhaust from the other, but as far as racing, the most free flowing that you can get to work is perfect, you will be spending all of your real time in the top part of the power band, so the power pulses don't matter.  In my day to day(to work and back) rides, I need power from as low as I can get to as high as I can get, all without getting a headache.  With my current exhaust, power at the top is great, I really can not claim about the low end yet, but I'm about ready to call it a day when I get to work, and that is about 11 miles.

Don
8)