rgtc said:Go to http://media.gm.com/division/2004_prodinfo/cadillac/pdf/04_Cadillac_CTS.pdf
This is a 2004 Cadillac CTS product information brochure. Go to page 6 where it gives engines specifications. You will see that Cadillac recommends 87 octane for the 3.6L and 91 octane for the 3.2L.
Compression pressure in the cylinder is what matters, not static mechanical compression ratio.IRWINVET said:You are certainly right according to the info in that product information book. Whats funny is that the 3.6L has a higher compression Ratio than the 3.2L why would the 3.2L use a higher octane?
I believe you are right about the ignition timing and you will also find about a mile better per gallon with the 91.silver bullet said:I am a first time poster on this site.I enjoy all the exchange of info. I have a 2004 CTS 3.6 luxury and sport package .My first US car in over twenty years and I love it. My owners manual says 87 octane is ok but for best performance us 91 octane. talked to several auto techs and they agree. I ran some un scientfic tests on my own . with the traction control off trans in sport mode it will chirp the tires. and move out pretty good with 87 in the tank. With the tank full of 91 octane same conditions it will really smoke the tires.so there is definately a power increase with 91, but it runs fine on 87. I feel that with the lower octane, the computer retardes the ignition to prevent pinging.