i have a stock 2000 300ex xcept i put a dg
exhaust sytem and k&n filter on it.ran it for
a couple hours,big difference in power with these,anyhow,it runs fine,but do i NEED to rejet?
also,i do not know if i have the right k&n,its about a inch longer then stock filter,is this correct?With these two mods,my 4th gear is much
more powerful.The DG pipe sounds hot,a bit loud though.

 

"but do i NEED to rejet?"
Only YOUR engine can answer that question;which means that you need to do a test/plug read.
For a ball park answer, the rule of thumb is to increase main jetting size one size for each air flow improvement and then back to the first recommendation.