I've used the FMF megabomb and Q4 on 2 bikes, trying both bikes with the Q4, with and without the megabomb. 01 WR250F and 09 WR450F. Neither bike came with a bulge in the header like the Powerbomb, as the later models do. In both cases, if there is a power increase, it's small. You would have to put the bike on a dyno to see it. But it does make the bike noticeably quieter so I was more likely to use the power that was there. So the megabomb makes a bike a little quieter with no restriction or loss of power. Worth it to me as I don't want to bother other users of the areas where I ride.
Edited by flyandride, January 04, 2015 - 07:42 AM.