Read how you can convert Gran Turismo 4 to DVD-R 4.7GB.
Make a folder (for example C:\GT4).
Open DVD Decrypter and choose Open -> iso-> read and press RIP.
When done, run Apache. Choose the image you just ripped and with right click on the image and choose extract all. When done, with right click (again) choose Switch layers.
Now, right-click one more time and choose extract all.
Note, you must extract both layers into the same folder. (Maybe apache gives errors when extracting the three folders. Better extract them with IsoBuster. When done you can delete the iso image. Open GranTurismo4.exe, and then open the GT4L1.VOL and choose ΤIPΤ.
When done run the runme.bat. It will erase the needed video files. When done, choose ΤKΤ (on GranTurismo4.exe) so the GranTurismo4.exe to remake the (smaller) GT4L1.VOL. You find the (bigger) GT4L1.VOL to GT4L1.VOL_OLD (delete it).
Copy the DVD iml2iso.exe, gt4.ims and gt4.iml into the folder GT4. Run DVDiml2iso and open the gt4.iml. Choose where the iml2iso save the iso image and press Start. When done, write the iso with alcohol 120% or Nero.