as long as you have an Intake
an exhaust the dc header isnt really worth it.
the dc header makes about 10 whp on its own and the TRD
exhaust makes about 5 whp on its own.
however, the Intake
/exhaust/header combo makes virtually no gain over just an Intake
so, in essence, save your money on the header and just get Intake
keep your eyes on the tpr header though..they aim to try and get a reasonable gain with the i/e/h combo.
and just some more fyi: ever current header for the celica makes virtually no gain as long as you already have an Intake