I just installed a Greddy TypeS on my evo from roadraceengineering. It doesn't have the single spring mod, so I connected the lower vacuum port. I noticed the blow off valve didn't engage at lower rpms, and only at high rpms making the dumping sound. I kept adjusting the spring but it still sounded bad, and didn't engage around 2000-3000 rpms.

So I decided to remove the lower vacuum port, and all I can say is wow. It sounds a lot better, and engages perfectly. I think I'm going to leave it this way, but would it be better to do the single spring mod since I'm only running the top vacuum port? Also what is so bad about not doing the single spring mod or atatching the lower vacuum port?

 

the single spring mod from what i have learned, allows the valve to open around 16in Hg of vacuum, which is supposivly close to stock characteristics, and also will blow off easier at low throttle situations. Boost still hold well because of the design of the greddy type S.