Assuming your talking about "pump gas" I wouldnt recommend anything in the oil but oil. There is evidence that the newer "SM rated oils benefit from a ZDDP/Moly additive like those from Torco, but pretty much all the additives you might find off the shelf at your parts store do little if anything of benefit. I would simply use a higher quality oil- like ENEOS, Redline, or Torco. I no longer recommend Mobil1, even if the factory does
For fuel the only injector cleaners I have had direct contact with are 44K, Redline SI1, and the Chevron with Techron cleaners, and they all work as intended. For a long time the only fuel injector cleaner recommended by Porsche was the Chevron with Techron, and I used it for a number of years with good luck. I have also used a lot of the Redline SI1, and it does a good job as well. In "normal" street cars like my BMW I generally run a 1/4 of the Chevron with Techron bottle per tank of fuel until the bottle is gone about every 15-20k miles. For the Evo I will simply run a tank of fuel with Redline S1 added and low boost every 15K miles.
Also, some octane boosters DO work, but are a hassle and expense I dont bother with.
