change to ext gate=increase in flow?

[leecavturbo]

will changing to a external gate lower back pressure and increase
power when O2/timing is optimised no other modification?
i.e same turbo but with the internal wastegate blocked off
and fitted to a new manifold with external gate?

 

[99gst_racer]

That would depend on where you're measuring from and where the gate is mounted.

If you are dumping one runner and not the other three, then there will be a difference in pressure in that gated runner.

You will not see a power increase though. The benefit to using an external wastegate is to better control boost.