Consistent Green Hill 2 Level Wrap 

Full jump on the rock, full jump to the very edge of the bridge pillar (pretty precise, it's a 16 pixel wide flat part), full jump to the flat terrain beside the rock with the yellow spring (EDIT: I suggest landing flush beside the rock with the spring with 0 horizontal speed and only then accelerate), walk over to the spikes, when somewhat close to the spikes do a 7-frame jump, repress a jump button so that you get a big bounce off the Buzz Bomber, enter the wall. From here, it's business as usual, hold right for 2-7 frames for a successful level wrap and a ~24 frame window to start holding left.
EDIT: here's a gmv to watch it with input display dehacked.2y.net...
Thankfully there's a backup should you get a 6- or 8-frame jump.
6-frame jump • gh2 6-framer backup
8-frame jump • gh2 8-framer backup