For those of you interested, I just installed my new FMF Power Core 4 on my 03, I like it, noticeable increase in power mid to top end, but its loud. I called FMF they said if its a new model the end cap and insert from the Q will fit on it, she said it gives better performance than the regular insert made for the 4 and is a little quieter. I oredered one for about $30.00 and I'll let you know what I think. Sounds pretty good I paid $230.00 for the 4 and $30.00 for the insert which is still less than the Q and it might be as quiet with better performance. By the way the part number is 040218.