I've found much conflicting info regarding exhausts, much to my dismay. 
1.  Does a full system (headers & pipe, ala V & H) offer significant gains over slip ons?  I wanna get power gains at minimal cost.  Have seen many riders using stock pipe from bigger bikes (i.e. r6, gsxrs, etc...), as a performance pipe on the GS. 
2.  Is there a possibility of getting a pipe that is too free flowing, ie, will my GS run worse with too little back pressure.
I plan to rejet as necessary, and get the K & N clamp on, to get more gas + air to the firebox.  In an earlier post, someone said that I will get no gains (only sound, perhaps) without getting new headers, but can't see spending $300, if I can get a slightly used can off a bigger bike and just weld it on.  Help if you can, laugh if you must.   

The headers are the most restrictive part of the exhaust. If you don't change them, you can't flow any more exhaust gas (which we'll treat like a fluid). Think about it.... if you took a coffee stirrer (you know, those annoying little thin straws) and tried to suck water through it, you don't get much water. If you take it and tape it to a regular straw, the end of it is bigger, but you still don't get any more water through the narrow part. If you reverse that to blowing water, that's about what you'll see with the exhaust.

Adding a stock can from a different bike just gives you a different exhaust note. A slipon, you can expect to see maybe a single added horsepower, if you rejet properly. That's about a 2.7% increase. If you do a full system + filter + rejet, you can expect to see roughly 10% gains, if you're lucky, which would put you at about 40-41 rwhp.

If you want more power, do the full system. If you just want slightly better acceleration and don't mind a sacrifice in the top end, drop the front sprocket one tooth to a 15T sprocket. If you just want sound, do a slipon.

YMMV.

thanks.  so do the full systems actually have larger diameter headers?  Or are they just bent smoother?  i guess after figuring in time spent trying to fit up and weld a can on, the extra $ isn't that bad for the ease of just bolting on a new system.  i already dropped a tooth in the front, probably will go +2 in the rear, if i can find one.

Y4

Full systems typically have 1-3/4" to 2" dia headers. I think stock is 1-1/4".

I kept the stock exhaust on my GS, but replaced the airbox with a "lunchbox" filter, and dynoed at 42 RWHP. With a full exhaust, I would expect 45+.

Bigger is not better, especially in terms of exhaust.

The gain from switching from a baffled can(stock) to a flow through can(aftermarket) is 95% of the gains.

The exit velocity of the hot gases, and pressure interaction between pistons is a huge factor in exhaust design. And considering most companies dont even make exhaust, the ones that do rarely do that much research.

Hell is the black yoshimera exhaust( the rare one) a slip on anyways.

Also, the power increase from the lunchbox is not that great, but when coupled with a exhaust is when it really hits in

Most people notice a great improvement when switching to a lunch box but most if it is the rejet

Quote from: AlphaFire X5 on January 16, 2007, 09:40:13 AM
I kept the stock exhaust on my GS, but replaced the airbox with a "lunchbox" filter, and dynoed at 42 RWHP. With a full exhaust, I would expect 45+.

I got 45hp with the full system and slip in airfilter rejet and dyno with no mods to the airbox (Jardine full system)

Quote from: coll0412 on January 16, 2007, 11:29:02 AM
....Hell is the black yoshimera exhaust( the rare one) a slip on anyways.
....

The black Yosh I had was full system.

http://img.photobucket.com/albums/v64/dgyver/GS500/91GS500R01.jpg

I have never dynoed my bike, but it has been Jetted and a vance & hines full exhuast was put on a long with a 15t sprocket and a k&N filter charger. My buddy has a stock 04 GS500f and he cant keep up with me at the lights nor on the freeway. if I hit it at WOT hes dust  lol ...

Ok...  Thanks for all the input, but I'm still corn-fused.  I think I'll do everything short of getting the full on system (i.e. lunchbox, rejet, up a couple teeth in the back) and see if I'm happy(er).  Maybe by that time I'll be able to more easily afford the V&H, or maybe Suzi will be making a black SV650 by then, and I'll just get one of those...  But in any case, I'm much less likely to just pick up a scrap can somewhere and start cutting and welding.  I'll probably spend the time fabbing up that luggage rack I've been meaning to make.  Thanks again yinz all...