whats the deal with the stock muffler is it true that there is a flapper valve that opens up at 6000 rpm and causes the boost to creep down....anybody have confirmation on this?????

 

It opens at wide open throttle. It shouldn't affect boost any.

 

well is it a bad idea to use the factory muffler with a aftermarket exhaust, it seems like its pretty big all the way through....but I dont wanna use it if it is gonna cause boost probs, or cause the car to run rich

 

the only real thing that is going to stop you from boost creep is your boost controller.