You can not build it for $15 anymore, the unit was $20 and the addition parts another $15. Buy still, for $35 its a deal.
The Whisper 2000 came from England so count on at least 4-6 weeks for delivery. I don't recall where I found it, search with google.
Click here for the article
Their unit completed -
My unit completed - <img src="http://e28-535i.com/upload/KD.jpg">
I just tried it out with the car at idle in the garage, seems to work very well. I will go against the recommendations in the article and drive with the head phone on tomorrow and see what I hear on boost.
I have some Panasonic noise canceling head phones I want to use with the unit but I need a stereo to mono plug adapter first. Should be just perfect for dyno runs
