Interesting information on cam timings as quoted from a post on bimmerforums.com:
Cam timing on the S50Euro and S54s goes like this:
RPM —- Exhaust —– Intake
Idle —- full advance – full retard – least overlap, best idle performance
mid —- full retard —- full advance – most overlap, best midrange torque
high — slight retard — slight advance – some overlap, cams moving back closer to idle settings up to rev limit
I’d be worried about exhaust valve to piston contact with stock M50/52/S50US/S52 pistons. There is very little room on the exhaust valve reliefs, which is why the money-shift bends all the exhaust valves. Retarding the exhaust cam makes it shut much later, which only exacerbates the possible problem.
Timing cams is not only delicate, but should be done with a degree wheel. I have cheated before and used the teeth on the balancer as a make-shift degree wheel with approx 3 degree accuracy.
Doing the evosport cams, I did the safe thing on the first install (recommended by them) by advancing the exhaust cam by about 9 degrees and retarding the intake cam by about 9 degrees. Dyno run showed poor midrange, but big power gains that would only be seen above 7200RPM. This was an IP car, so that was out of the question for engine longevity. These cams are huge with long duration, so I was not about to bend up the valvetrain by setting them in with the cam blocks. Next time around, I set the exhaust cam to about 3 degrees advance and retarded the intake cam about 3 degrees (from factory spec). Midrange torque jumped. If you could retard the exhaust cam even more without fear of hitting the pistons, you will see even better midrange. Idle may suffer, and there is a point where you will lose high RPM torque.
Advancing the intake cam helps the midrange, which is why the factory VANOS advances the intake between 1800 and 4800 (or so). The reason people see some gains in top end by retarding the intake cam is because that is what makes torque up high. You will probably lose midrange torque a bit. Limiting the VANOS advance helps prevent too much overlap on big cams such as the evosports and Sunbelts, and you can leave the intake cam timed properly.