Long story short I've got an 06 6MT with:

z-tube/ K&N
MREV2 & 5/16 iso
Fast Intentions HFC and cat-back exhaust
GroundingGear 6MT performance hyper-grounding kit
Osiris Tune coming soon

For the next step (before the tune) are unorthodox pulleys worth doing? Has anyone experienced any issues related to the underdriving of the accessories? My dad used to build cars "back in the day" and thinks its a complete waste of $280...

Who's done it! Thoughs/ impressions?

 

I have never seen any factual evidence to suggest that they do anything to improve acceleration or any other performance figure.

If they are under-drive, I have heard of a few issues that may arise from them.

 

The websites are telling me that you'll gain around 2.7 hp for every pound you lose on the crank pulley, and with it weighing 5 lbs less than OEM if that number holds then it sounds like a great mod... but they don't exactly have any empirical evidence to convince me of this ;p

 

It's BS. Do a search for "UDP" and "DaveB". There will be plenty of information there for you to decide if this a mod you want to do.