I had a 406sbc built about 2 years ago. D-dish hyper pistons, 9.7:1 comp, heavily ported 461 feulie heads, air gap intake, 1 3/4" headers with 2 1/2" full exhaust with Dynomax super turbos, etc with a XE274 cam in it. Yes the idle was noticable. Like a mild anger! Not pro stock evil or anything, but healthy. Certainly enough to get a few disaproving looks from some neighbors. I imagine a xe268 in a 383 would be a little bit tamer than a xe274 in a 406.