I have on 05 VIII stock. Had it for about 5 months now and just turned over 60k miles. My issue is one that I have never seen happen to anyone else before. I put on an open air filter with the adapter, I took it for a test drive and as soon as the boost kicks in it lags badly and if I keep my foot in it, it shudders. Now when I put the stock airbox back on... It runs fine and holds boost like a champ. Is there something the stock box has that the adapter doesn't compensate for? Or is it just a tuning issue or could it possibly be a bad MAF sensor or something more serious? I have retarded the timing slightly to lean it out just to get rid of the knock count, but that is the only tuning I have done to it.
Any idea's or suggestions would be a great help!

 

you are running rich with the open element filter and/or it could be the maf adapter

 

I thought it might be the maf adapter too. I tried it again the other day and tried to lean it out some more, still does the same thing. In fact I leaned it out so much that I throw the P0171 code. I didn't think it would make that huge of a difference by just sticking on an air filter, has anyone tried the Vibrant 4.5 inch adapter?