I use the castrol synthetic out performance. I had used regular castrol for a while but decided to switch to full synthetic. I wouldn't say you see any performance increase but I do go 6k between changes now (about every other month). Even at 6k the oil is still clean and the filter is still light.

 

I use Valvoline, or Mobile 1 FULL Synthetic , 5W-30. with either K&N oil filter or Fram 5398A oil filter. there is a noticeable change in power, and how much faster the engine revs up when you switch to synthetic. The only this is once you use synthetic, DO NOT USE REGULAR OIL AGAIN, you have to use synthetic all the time, its not good AT ALL to switch back and fourth.

 

Also be careful with lucas stabilizer, if you add to much it will lock up your motor, its like glue, read the directions very carefuly, also hyundai motors excluding the 8cyl in austraila, do not like lucas, if you have a bad oil leak due to piston rings, valve seals, then use it sparingly, hyundai motors are fast reving engines, lucas slows up the rev speed

 

i use GTX as well.

 

i used to run castrol
switched to Syntec

and im now running mobil 1 synthetic

 

Nothing but 8100 Motul synthetic.

 

Quaker state 5w-50 Full synthetic

 

see..... i use castrol GTX... but this last time my buddy convinced me to toss in some 5W-20.... was this a bad idea... i live in the NW corner of MO.

 

castrol gtx 10w30.... cheap and i change my oil every 2k.... least amount of expanders cuz the temp here doesnt fluctuate to extremes

 

Mobile 1 Full Synth, good stuff. Change between 5k & 6k.