I just installed the spacers and went for a 25 mile cruise. Overall, I think the biggest improvement is that it seems like there are less vibrations in the car and because of that it seems like the overall volume inside the cab has gone down and that there's a little less drone; however, the drone is still there. It was also hard to judge as it took awhile for the engine to warm up (it was about 50F today). Most of the ride I was under 180F water temp but I did notice that the hotter the engine got, the more the car droned. I think the next step will be resonators before the mufflers.