Installed my new F1 mach 3. 8's last week and boy what a change. Kept track of EGT's on my usual run before and after and found straight cruising with 5000lbs behind lowerd 100 degrees from the DD2's. Pulling short grades about 50 degrees. All on cruise in OD at 60mph. Idles quieter and milage went up on last tank 1. 5 mpg. Bought from Bob Wagner, great service and pleasant to deal with. DW