i've got the JR VPAC. For one thing i was quite dissapointed when i received the thing and read that i could only turn vtec down to engage at 4000 when the dial goes all the way down to 2500. I was under the impression that it could go all the way down but it says you must have a turbo setup or supercharger to be able to engage it that low. I have it set to engage at 3800 right now and am not noticing any problems with it being at that point. The only other real problem for me was that it was a ***** to install because the little crimpers that they send you are a pain to work with because you can't get a good connection. But despite that i think it was a good buy and did notice performance gain, nothing major.