What synthetic? I ran synthetic in my GN when it was stock and wiped the cam 2 oil changes later. Here is the thing with these motors. They don't have roller lifters and need mire ZDDP than modern synthetics offer to keep a protection barrier between the cam and lifters....especially the turbo Buicks. Why? A manufacturing flaw. See, the lifter on a flat tappet motor is not supposed to be perfectly centered on top of the cam lobe. This causes the lifter to spin in the bore and wear properly on the cam. On our motors, the #3 exhaust lobe has the lifter bore centered over it. Unless you are using an oil that has plenty of zinc and phosphorous in it, there is a good chance you are going to wipe that lobe flat over time. Then the next thing you know, the car is slow, does not spool well, has a funny exhaust note when you drive along a wall that makes you think you have a header leak, etc. After doing a lot of reading and filtering out the BS, your best in store oil IMO is Valvoline VR1 conventional racing oil. I only use that and add a 1/2 bottle of ZDDPlus to every oil change. This opinion was derived after reading a bunch of Richard Clark's posts on the subject. Also NEVER use Fram again as others have said. Napa Gold or Wix are great filters that you can pick up at the corner store. Hope this helps.