if the tune is decent the idle will be a non issue. TSP is playing it safe which is what they should do. A 224/228 would be a BABY cam in a 408 and I guarantee you will want more. The LSx 396 in my old racecar was a 286/303 with way over .700" lift and with the right tune and backpressure hte idle sounded about like that of a cam only car, a little more throaty, but no more choppy or nasty sounding.