We have not had any problem last yr or this yr. My dad ran a 79 N6 with a l10 in it for 3-4 yrs no problems. We have 2 42 foot hb on my two machines as well a 30 foot flex head and 12 row 30 inch corn head and a pickup head, my dad runs a 36 foot hb head as well as a pickup head. When we cut for our customers some of them lay down two 30 foot swathes, that we pick up. When we are going speed is NOT an issue we don't push the machines hard we stay right were the sweet zone is, we like to save all the grain we can for our selfs and our customers. The added horse power is nice to have but we do not abuse it. Yes we have staight pipes on all three. As for fixing the engines we have had great luck with our cats. We have 2 C16 in our highway pete's and 2 C15 in our tandoms, we have always owned cat engines, and our dealer has always treated well.