I've been using a 3 port by supplying pressure to the top port of a Tial external WG, and not hooking anything to the lower port. I've never hooked anything to the lower port of the WG. It's always worked pretty well applying 45-60% duty cycle to increase boost 40-70% above the spring pressure. I.e. - 10 psi on spring and 15-17 psi at 55-60% DC. Why would I ever want to hook boost pressure from the manifold to the lower port? Wouldn't that work against the spring and whatever the Mac valve is supplying to the top? And wouldn't that require more DC to maintain the same pressure in my example above? And most importantly, wouldn't that decrease the maximum boost generated at 100% DC?

 

Because a lot of times the drive pressure isn't enough to crack the valve open by itself and you need pressure on the bottom port to open the valve. Say i've got a really good flowing combo with a great turbo cam and I have a to# spring in it but I want to make 8#. Can't add to the top to lower the boost, so I need some in the bottom. Keep going with that scenario and you can see how a turbo could run away with you if you won't have any pressure to the bottom.

 

Okay. I’ve never had the issue of not having the WG open at spring, but makes sense. Thanks.