Hi,
Loud is a small word. The windows rattle in the car, alarms go off in far-away countries and kids tremble in fear. But seriously, you could not drive with them fully open all the time, it is just too loud. At idle, there is a very plesant deep burble, moving off at normal speed, the noise is not so pleasing, but on full acceleration, there is a glorious noise of a snarling V8, free to express its inner demons. On over-run, it spits and crackles delightfully. The flaps are capable of being opened in incremental amounts, via the remote control, so you can play with different noises, or none at all. The advantage of a remote control are firstly the lack of need to position a switch and secondly, you can stand outside the car playing away with the exaust, amazing all and sundry.
I did research what effect the reduction in exaust backpressure would have on a V8, and the general consensus is that it it reduces low end torque but increases top end touque (correct, in this case). The only concern is the spitting and popping on the over-run, from my racing days I seem to remember this can cause 'hot-spots', in the motor, so I try to reduce the amount of 'over-run' with the flaps open.
Other than that, they are great fun!
Will YouTube in the next few days.
Pat.