1989, 930 with 15k miles. I have the choice of either non Ethanol Rec 90 Octane or Shell/Chevron 93 Octane. Does anyone on this forum have an opinion on which gas would be better ? Also, the car has been running on Rotella T4 15W40. Is it Ok to continue using this oil?

Thank you.

 

Is the Shell/Chevron 93 Octane non Ethanol? If so, I would go with that, otherwise, I would recommend non-Ethanol 90 Octane and treat with BG 44K that will boost the octane.

 

Thank you for the recommendation. The Shell/Chevron has Ethanol. I'm concerned with adding the BG, since I only drive the car a 5-6 miles per month?

 

BG 44K in the tank will be good if your car is not driven much. The stuff is awesome but expensive. I've never seen a negative review.

 

Do you have a local racetrack nearby? ... where you could pick-up a 5gal gas can of {something like a Cam2 purple 110) per each of your other purchases of non Ethanol 90 fuel, and run a mixture?

Cam2 Purple has lead too (which is good for our valves), and it is a true 110 octane,... verses trying to bump a 90 up with BG44K, which IMO does a better job of "cleaning" than it does bumping the final octane rating of a tank of 90 street fuel.

Also not sure of your Florida laws and whether you have O2 sensors on your exhaust or not. If you do, then the leaded 110 octane is not going to be good for that sensor.

driving it only 5-6 miles a month means it sits a lot,.. and the street fuels today just do not have very good shelf life. I drive my 3.3 964T all year long (or at least in the winter I wait till good dry, salt-free roads),... but it can indeed sometimes sit for 2-3 months at a time. The Cam2 Purple 110 leaded has a fantastic shelf life. I've left it in my 1968 Big Block Camaro (396/375) tank for up to a year & it still fires right up & runs strong.

Anyway,... just thought I would chime in with an option. ... take it or leave it.
Good luck,
=Steve