Yes they do make a pretty big difference.

If you were primarily flying IMAC, and not that interested in hardcore 3D, I would recommend getting the pipes for sure. If you want to do a lot of 3D or that is the primary purpose for the plane I would just stick with the cans.

The pipes will give you a lot more high end tq (1/2 throttle - full)
ex: in last years unlimited sequence when there was the 1 3/4 snap without pipes if a plane came into the snap at 1/2 throttle and lost a lot of airspeed the extra load on the prop would make you have to add a lot of throttle quickly to maintain airspeed. With the pipe, the added tq would help keep the RPM when it loads up and the plane does not slow as much.

They are great for pattern but when doing 3D with them you don't have a full linear throttle curve. It will start off nice and smooth for about the first 1/3 throttle and once you start approaching 1/2 or just a little more the tq from the pipe starts kicking in and the RPM starts trying to jump a little (just not smooth enough for me the way I like to do 3D, makes tail touching hard b/c every time you give it a little extra throttle you usually get more RPM than you want and you end up climbing 5-10 ft.)

Hope this novel helps

If you have anymore ?'s let me know or maybe someone else will chime in on this thread and tell us there experiences with the pipes so you can hear more than one perspective.

John