External Wastegate, Boost Soleniod Q's

Ok so fit a Boost Solenoid to a car with a external Gate the other day... Tial gate so went to the Tial website for info, and their page says follow the instructions from your boost controller

It was a Haltech boost controller and came with these instructions:

http://www.haltech.com/wp-content/uploads/2011/01/HALTECH-BOOST-CONTROL-SOLENOID.pdf

So I followed them and connected it up... And well everything worked great, with slightly less boost threshold then the car had with the Manual Tee...

But I have noticed bout the place that most places say to connect to a external wastegate like so:

So its working fine now, is connecting it like that a big benefit? will it help to hold the gate closed better and decrease boost threshold even more?

Yes!

The solenoid applies boost pressure to the top chamber, aiding the spring to keep the wastegate shut firmly.

If I was to change my hose arrangement to be connected to the top and bottom half of the external gate as pictured would you expect me to need to re-tune the PID's or the base duty cycle table (feed forward) or both...

I would suspect, that you'd need to change the feed forward table slightly

It looks like the Haltech diagram is for an internal wastegate. The connection for an internal vs external wastegate are different (although I've seen many people apply an internal gate hook up to an external wastegate and still get acceptable results.

With most internal wastegates we only have one port, and applying bost to the port opens the wastegate and hence reduces boost. To correctly plumb the solenoid to this kind of actuator, we want the COM (common) port connected to the wastegate port and the NO (normally open) port connected to boost pressure. In this method when the wastegate solenoid is not energised, the boost pressure will be connected directly to the actuator and we will get minimum boost. When the solenoid is energised, the COM and NC (normally closed) ports are connected which means the pressure in the wastegate actuator vents to atmosphere and the boost increases.

On an external wastegate we can apply the same principle and it will work, however the recommended method is to supply the boost pressure to the top of the wastegate as per the diagram you attached. I generally find that with an external wastegate this will provide more stable boost pressure.