I know i have two exhaust leaks in my pipes one towards the middle and another towards the forn by the engine. Every time i step on the gas past 1/3 it makes a hissing sound. Whats causing this and what can i expect to fix it. Thanks Also one more question if you have 1 or 2 bad spark plugs will you have a loss of performance thanks

 

Yes to the plug question.
If you have an exhaust leak and you know this, then you already know what is causing the hissing noise. A permanent fix is to get it replaced, a temp fix is to use those "bandaides" offered at autoparts stores.
Does your car sound loud at WOT? As if you were driving a car with a straight pipe, no cat converter, and high flow muffler or just a pipe? If yes, then get your exhaust replaced. If no, then give us more info. How do you know that the hissing is coming from the exhaust pipes and not from an air leak from the intake tract?

 

I really don't know it just what a friends telling me plus it only does it under moderate to heavy acclerations my friend says it the pressure coming out but sound like its whistling when you're moving fast.