i thought there was a mechanics corner, but seeing as though this applies to my bike i dunno.
SO, i understand it scavages fuel from the exhaust stroke, that back pressure will obstruct the flow. and at some rpm ranges this will happen differently?
now for the problem, why do i have a 1-3/4 inch pipe? does anyone know the size at the headers? why wasn't the bike designed with 2'' headers?
if im coming into a bigger muffler from a smaller pipe, and the baffle is bigger will there be restriction? will a series of smaller baffles with the more space be quieter and less restrictive?
does more insulation around the baffle dampen more of the soundwaves? as if i get a 2 inch baffle and 4 inchs on the outside is packing instead of 3.
i read if you pack the insulation tighter it isn't as effective, but if you don't it will blow out or compact itself.
is the baffle the only thing that constricts air flow at this point?
anyone know what the best gains would be going up in size on the headers would be and what is the biggest before its ineffective at power gain?
how does one make an exhaust quiet while producing power!?!?

 

OMG dude so many questions. The larger the exhaust pipe, the more volume of gas it can flow. Eventually it becomes too big and slows down the exhaust flow too much. Going from a small tube into a larger one is called step tube and will increase flow as the exhaust now expands into the larger pipe it pulls the stuff from the smaller pipe with it [thats scavenging pure and simple].

To simplify all of this: if your not designing a perfect exhaust header for the specific application then you can't run no backpressure without negatively affecting the cylinder scavenging.

 

im getting conflicting info everywhere, so the only way to find out is to get understand how it works. its nice to know stepping up the size is what is going to increase flow.
it seems, to me, slip ons will give gains on paper and i want to have increased flow but i damn sure need to keep it quiet.
im going to assume after stepping up if i put anything in the rear like an insert that will probably decrease the final exit size, to make it quiet, that it will start constricting.
my curiosity led me to think about 3 or so of insulated baffles while maintaining the same overall air flow space because it seems to make sense.
i cannot design this or weld it, but what i can do is make more insulation around an existing 2 inch baffle. but if its just better to buy a quieter 2 1/4 inch and fell ok about not retuning, then i will do that to be done with it.
i would just feel better if i had some numbers i could put in diameter and length and understand how the flow is actually going to be.. ARGH this sucks.
unfortunately the thought of a full system on sale from $600-700 is making me wonder if thats enough to be thoroughly engineered to increase gains by 10%
its very safe to say im at 100 hp currently so if we talk percentages it should be noticable. i am going to track this bike, i was going to go yesterday but i destroyed my slip on after reading about how someone could ruin my day with a SPL meter

 

Different engines flow air through them differently period. Take the 600 f4i, and a stock air filter and exhaust then look at the dyno chart. Then replace the air filter and exhaust system making it flow more freely. The side effect will be a terrible low end and bike may fall on its face around 2200 - 2500 rpm where it naturally has a flat spot in power and torque. But the gains at the higher rev range are shown. A larger exhaust doesn't have to be installed to increase horsepower in fact a lot of times installing exhaust that is too large (for a non modified engine) will hamper its performance making it act more like a two stroke per say.

As exhaust gasses are expelled into the header from one cylinder, the companion cylinder is dependent on that pulse to a degree via the header to pull air across a cylinder (scavenging) from adjacent pulses, so if the tubes for the header are too large this effect is degraded and performance is effected. Likewise airbox volume greatly effects the performance of an engine and if you would remove the airbox to make a streetfighter or what not and install air filters directly on the throttle bodies, you would not only kill the ram air effect, but destroy the performance gains from the enlarged airbox.

Simple differences in the packing of the muffler and the style of the core can increase or decrease flow and power at different rev ranges. d&d exhaust cans for example come with a perforated core and are wrapped tightly with insulation sheet then fiberglass tape. You can remove the insulation from the core and replace it with loose fiberglass packing and it will be much quieter (at least at lower revs) without effecting flow severely. The downfall is that you tune the bike for this and as the packing slowly blows out it will change the flow and require adjustment and the can will run warmer than it did before but I did this and managed to gain a couple hp more than the factory d&d and kept the police from stopping me for loud exhaust.

About back pressure, being measured with a manometer most people don't have or use. The most important thing about back pressure in my opinion is that if it isn't correct it can cause engine damage. Every engine requires x amount of back pressure and too much or too little can be detrimental. Burning valves is common if you have added boost and things aren't set up properly on a bike, as they aren't set up for high back pressure. You are looking to lower it and that can make it run strangely in lower rev ranges.

If you go with a bigger exhaust on a fuel injected bike, It may breathe better.. meaning more air. You should be safe and add more fuel to it on a dyno (power commander and tune will cost you about 600 - 700 average depending on where you live). It will not only run better, but it will likely last longer by not running too lean. I hope this helps.