Which external wastegate?

[CNHSS1]

i had an ebay cheapie too Gripo, was fine. Only problem was i ran a screamer pipe and it used to 'chuff' at idle, didnt seat perfectly until about 1200rpm. Sounded good at full throttle.
if i ran one again, i would run the ext wastegate exh pipe back into the main pipe after about a metre from the turbo. does stop the noise a fair bit and stops the scrutineers asking why i have two exhaust pipes at scrutineering

from what i know, the sizing and spring pressure is based on two things, amount of gas flow and what boost solenoid you are going to use.
if you have a small to medium flow turbo, then a 60mm ext WG would be overkill as soon as it opened it would bleed off a huge amount of gas and actually cause an erratic boost curve. ideally a 38mm-45mm is fine on most turbos imho.
With the spring, go for a spring rated at the minimum amount of boost you are going to run, then youre boost solenoid will bleed off enough to give you 'overboost' ie spring at 14psi, with boost solenoid closed, then say 20psi with it open.
I had a problem with my boost solenoid on mine. with the boost solenoid fully open i could only get 12psi, so i guess the spring was about 7psi. i changed the boost solenoid to a 225 Audi TT version and that helped, allowing 15-16psi max.

hope that helps mate
CNH