Car and Driver had 92 listed in there article but the same Cadillac motor is listed as regular! What gives? Will it run on regular? Or is like 91 or 92 or higher recommended? What do you GXP owners put in yours? Thanks please respond Chris!

I have never put anything other than 93 octane in my GXP. I try to stick to the premuim brands as well... Chevron or if not available Shell or Amoco/BP

The owners manual says it will run on all octanes, 87-93, but I have a hard time putting the lowest in mine. I am used to my 95 that needed 92 or better for the supercharger. I have ran regular in the GXP twice and had no problems. I primarily stick to silver(BP Amoco) which is 89 octane, I think.

It all depends on engine compression. Early Northstars had high compression ratios (10.3:1) like in the 4.0, however after 2000, the 4.0 and 4.6 were lowered to a modest 10.1:1 compression so premium wasnt required.

I bet dollars to donuts the GXP 4.6L V8 has 10.1:1 comp therefore low/mid grade gas is acceptable.

As far as I know, my wife uses 87 octane in ours with no concerns.

When I first got my GXP I always put 87 in it but then started thinking about the compression. I know my 98 GTP needed 92-93 if you ever got into the boost but it could deal with 87 in emergency situations. (or if the stupid dealer makes your "free tank of gas" when you take delivery 87 because the dipshit detail kid cant read!) It says clearly on the tank door in big red letters Premium fuel ONLY. The GXP doesnt have this so I always questioned it. I think I'll try a full tank of 93 an see if I notice anything different.. prolly not.

I am not too Savvy, but what is the potential Impact of using 87 vs 93 octane?

I remember that in the Dealer Brochure is said it uses 87 Octane, which was different that other cars in its class. I know 93 can't hurt, but isn't this the age old argument about the benifits of premium gas in engines not designed for it?

I mean in terms of testing for improvements, what should be looked at? MPG? I don't think acceleration improvments, or engine performance overall could be detected just by "feel" when switching octanes. Are there any long term disadvantages to using one or the other?

Any insight would be appreciated.

-Ian

Personally, If I owned a GXP, aka. expensive car. I would run 91 atleast. Like we've heard before, running lower octane sometimes wont make a difference cost wise, if you have to fill up more frequently with regular.
just my .02

As if they wouldn't?


Anyways....I'd run 93 or better if I could.