It's probably not helpful to tell you not to do it without explaining why.
When you open up the exhaust you lean out the air/fuel mixture. Leaning out the air/fuel mixture creates intense heat. Intense heat fries things like valves, pistons and $$tuff.
If you've ever used an oxy/cetylene torch this is a bit easier to explain. You can use an acetylene torch to heat up your coffee cup if the flame is rich. You can also use it to weld metals together or to cut through 1" steel plate just by leaning out the mixture.
Your engine works the same way except instead of acetylene the fuel is gasoline and the oxygenis provided in the air entering your engine.
This is an extreme example of what can happen. Running lean can have varying effects in between, but it always results in excess heat. Up to a point you can cool things back down through jetting (adding more fuel for given unit of oxygen). Running without a baffle is likely beyond that point.