I have an Xbox 360 with LiteOn 74850C.
I also have an old Xbox Hitachi dvd drive.
Since I am new to this and didn't want to screw up any original parts, I flashed my old Hitachi drive using Jungleflasher.
Then I dumped the code from the LiteOn using probe3 and spoofed the Hitachi.
I put the Hitachi drive in my 360.

I don't have any copied games yet, but I tried some originals. Old ones, like Fifa 11 or UFC 2010 work well, but newer ones (Halo: Reach, FIFA 12, Forza 4) don't. The thumbnail is shown in the dashboard, but when I click on it, it's like the game is starting to load, but then the screen minimizes and tells me the disc is 'dirty'.
I already tried modifying the POT meters, no luck.

Any ideas?

Sounds to me like that hitachi drive is older than 78/79 and does not support AP25 processing.

That might be your issue.

that wouldnt explain fifa 12 not working, no ap 2.5 checks on that

Yes, it's a 47 drive.
Isn't it possible to play newer games then? An unflashed drive should be possible to play new original games, shouldn't it?

-edit

I just did some research. I believe it isn't possible to place a Hitachi v47 in an Xbox with original LiteOn, because if you spoof it, the Xbox wil think it's a LiteOn and you can't 'check' AP2.5 games with the Hitachi.