You have to drill through your pipes to install these properly.

I tried using the bolt as a set screw to hold them in, and blew one out after about 4 uses.:party-smiley-004:

I also think I was losing quite a bit more than a couple mph, but they did quiet it down.

This is correct, I am notching the tips and using a tach weld that one you slide them in you will rotate past to solve this, using the set screw to keep it from rotating.

It does say right in the add not for more than 425 horsepower so I expect to lose performance, no doubt about it. Since my tips are so short and I have flush tips, it was about my only good option without spending money for something I'd rarely use. I guess what can you expect for $80.

Did it freak you out when they flew out?

These slip ins are held in by a 1/4" bolt threaded into the nut that's welded into the muffler and an additional nut used as a locknut , added on to keep everything together safely. I use them in my tips of the 6.2 MPI engines in my boat [ less HP than the max rating for these mufflers! ] and used them in 450 HP engines as well ,never blew one out. One can drill a 5/8 relief hole in the center of the baffle to lessen back pressure and still maintaining noise reduction.Just a thought if you worry about blowing them out.