the xk magnums are, from the two I have worked on in the past month, strange beasts. all magnum exhausts seem to want to slip off until you get a good system worked out to hold them on - the one it comes with hasn't cut it on any of the 7 magnums we've got here in sf. We hacked at our 1.5hp xk- drilling a few more holes in the inside of the exhaust (where the MKII has them and the XK doesn't), switching the 12 intake & 12 carb to 14. Tonight we switched a new xk's engine for a maxi 2 speed. Most xks seem hobbled, and capable of much more with a little tweaking.