In my TR these did nothing. I found sticking with the CR42TS seems to make the best power with the best reliability
However in my wifes 03 mustang GT with 4.6 SOHC with intake, shorties and exhaust we found a little more power, smoother operation at idle and about .75 more to the gallon.
I have not tried them in the lt1 yet so that is next.
I would like to see what they do in a boosted LS setup. Maybe next year I will be able to test that.