I have had good luck with FMF and Pro Circuit headers and mufflers on my different bikes.
My son has a stock (except for jetting) Honda CRF80F. I'm thinking about upgrading to an aftermarket header and muffler setup such as from FMF. http://www.fmfracing.com/Products/BikeA ... NDA_CRF80F
Has anyone done such a header/muffler mod on a CRF80F ... and if so, did it make a significant difference in power?