The exhaust won't scavenge correctly and actually get pulled back into the head and increase the temps on the valve. It will also affect the intake pulse. Its called reversion. You get stuttering, carb coughs, and a dead spot where it stumbles really bad when you give it throttle. It will go from lean to extremely rich. causing the exhaust valve, guide, and seat to run very hot. It can't be timed or tuned out. Not to mention that running lean increases the temps of the cylinder, causing piston and ring damage.
A car has a long intake tract/runner length that can handle exhaust changes a lot easier. On a bike, the exhaust is a key to tuning. When you make it flow more 'air', it does the same to the intake side. You get more air, but no extra fuel. Same with a change to a free flowing air cleaner. You also lose lower RPM power and push peak power farther up the RPM range. An open pipe makes carb tuning impossible because simple things like ambient temp, humidity, and barometric pressure will change the flow characteristics of the carb on a daily basis.

Baffles allow you to make power wherever you choose by changing their length and increasing/decreasing the openings. You must also pay attention to total exhaust length. Too short and a baffle does no good. Too long and you can cause it rev like a slug and build excessive heat because it fills the pipe quicker than it can escape. Nothing beats a good performance type muffler/exhaust.
I copied a Buell XB12 engine perfectly. I could get no closer than 12hp and 19ft/lbs of power less than a Buell. The only reason was the exhaust. I could not copy the flow characteristics without being an eye sore. I took an old frame and cut it up to make a Buell system fit for a dyno run and it was within .46hp and 1.1ft/lbs. That was the key...the exhaust. So i simply bumped the displacement to get the same numbers. It cost the owner an additional $1200 in parts because he wanted to keep the Sportster looking stock.

Anyway, unless you wanna 'look cool', be obnoxious, or drag race-leave the open pipes for the track. I've fixed many a motor because people think they know how to make power. My project now is a Yamaha XS 650 with the top lands of both pistons melted and the rings fused to the piston and ate the walls so bad that I have to replace the jugs. The heads need new exhaust valves. Pretty much a rebuild because the guy cut the pipes off at the bottom of the frame and added a new main jet to make it richer. problem is, there is also a pilot/slow jet that runs the bike to mid RPM range when the main takes over. He putts around town mostly and after the last rebuild (2600 mile before) when it was stock (1900 original miles) he got to enjoy it for only 9 months. The repair will cost him more than he paid for the bike and the last rebuild! All he had to do was 'read' his plugs after he and his buddy made the 'performance mods'......

A funky baffle. Buy one from a catalog and install no closer than 2" to the outlet. You tune it by increasing the hole diameter of half of the holes 1/8". Want more flow, do the other half....keep doing it in 2 steps till ya find what you want.
With yours, I would open/close the tab till I found what I want. Always give it at least a trip around the block at low and high RPMs and read the plug to find out if you need to rejet up or down. Now, really important here, Your carb should have 2 jets and a needle. Almost NEVER do you need to replace/modify all three unless you have internal engine mods. Lancer has a very nice kit and others on here have some nice carb tuning info.

I just feel i am in a tight spot i want more sound from my stock bike.I hear the dyna swaps are nice but dont like chrome!So i dont know where to go i have looked at the BCB muffler but have a hard time paying that kind of money for a pipe and a baffle i could make.But then again i read on here drag pipes are not very good for your bike i am torn on what to do and it is holding up my project.I know i will need to rejet the carb and i am waiting on lancer to get better to get his kit just cant find another option that fits my wants.Any ideals?

Has anyone ever used power cones?It goes in the header pipe and is suppose to give u that back pressure you need while still letting you run drag pipes.

Had an ideal today what about a 4 inch baffle installed in the header and a turn out tip.Or maybe install baffle in turn out tip.what do you think would it be enough back pressure?

I'm sure not a tech on it, but I doubt the lack of back pressure in itself will do any valve damage. Its would be the cold air dumped on the valves at shutdown that can cause damage. I can remember rodders capping  stacks quickly after shutting down.
But, God knows I've run a lot of strate pipes in my day, and I never seen any valve damage.

Routy wrote on 04/17/11 at 06:52:29:

Thats the difference between cars and bikes. Cold air isn't the issue unless you have a very short pipes (like open headers on a car), then you would have to worry about bending valves.

You may have run straight pipes for years, but you have evidential ran you carb rich too. I have run straight pipes for many years also, and have become very good at valve jobs because of it. if you read the above explanations, you'll see that there are many factors that come into play.
Torque cones that go in at the pipe at the head have not been proven to do anything. A 4" baffle is the best place to start. The end (outlet) of the baffle should be no closer than 2" from the outlet of the pipe. If you pipe is long enough, you may be able to get away with 'lollipops'.

And here, this is from a burnt exhaust valve (open pipes and improper tuning) from a lean condition. Valve face split bounced around long enough to do this....


And for torque cones....

Anti-reversion cones are a device you put into your head pipes, near the cylinder head, to discourage reversion (i.e. a positive pressure wave in the pipe that interferes with cylinder fill if it arrives during overlap). Some are bell shaped like pictured above and others are a pure cone shape.

At various times I've tested these things (both styles) on exhaust systems that both showed and didn't show evidence of reversion. The results have always basically been about the same ...


They always seem to either cause a small loss over a wide range, or on occassion I'll see a small loss at only higher rpm's.

My guess is they'd be more effective on a system where the pipe was oversized for the motor size and target rpm. I'll continue to test these as I get time and if I get a result on a particular setup where they show a real advantage. In the meantime, it's not high on my list of worthwhile performance mods.