It might take some time, or even another fillup to reset the slightly retarded timing for 87 octane. I would just go easy and don't lug it till then. It should settle down, but I don't personally know from experience.

 

You are soooo right on the "snake oil additives". Sheesh, just the thought of putting something like that in the tank ..................

 

A letter to car manufacturers from the EPA:

http://www.epa.gov/otaq/cert/dearmfr/vpcd9701.pdf

An excerpt from the letter...
(NOTE: FTP is Federal Test Procedure, SFTP is Supplemental Federal Test Procedure, HWFET is Highway Fuel Economy Test, and finally 91 RON and 96 RON is equivalent to 87 PON and 93 PON or what we refer to as regular and premium.)

(Quote) Under the provisions of section 27 of 40 CFR Part 86, EPA began to require manufacturers to show, prior to certification, that knock sensor equipped vehicles could operate on 91 RON gasoline without effecting emissions or fuel economy. To do this, manufacturers have to demonstrate that the knock sensor output does not alter spark timing during FTP operation, or that the fuel economy difference between 96 RON testing and 91 RON testing is within 3 percent. Either option requires the manufacturer to run special testing.
...
EPA has rarely found that knock sensors come into play when tested with 91 RON fuel. There is no likely motivation for a manufacturer to design a calibration that results in spark retard while operating on recommended regular octane gasoline. Therefore, in lieu of test data, EPA will require that manufacturers submit a statement attesting to one or more of the following:
1. The knock sensor does not activate in any way during the FTP (or the SFTP as applicable) and the HWFET, and the calibration is designed to operate on 91 RON gasoline without the need for spark adjustment.
2. The city and highway fuel economy test result differences between comparing 91 RON operation and 96 RON operation is within 3%, and there are no emissions increases (beyond normal test variability) using 91 RON fuel when tested on the FTP (or SFTP as applicable). (Unquote)

...Hope this is what you were looking for.

...Note that FTP and HWFET are done at light to moderate throttle with A/C off and moderate ambient temperature, not 90+ degrees (remember knock is less likely at lower throttle opening/load and temperatures). Given those conditions, 87 octane would work with very little spark retard allowing GM to stay within the 3% window.

...Pinging (light detonation) will not harm your engine, your knock sensor obviously allows more than others or you have very good hearing. Either way, I'm sure as the octane goes down, more timing would be pulled out...or maybe even boost gets dropped (do you have a boost controller managed by the computer??), I don't know what options your computer has. In addition, you only have 8.2:1 compression so I would think timing retard would easily control knock at full throttle.

Also, an interesting read is http://www.caranddriver.com/article....&page_number=1

 

Suggest you do more research before piping in.

 

the '05 Owners Manual states that 87 Octane is acceptable but 91-93 is recommended. The knock sensors & electronic engine controls will adjust timing to avoid any pre-detonation worries & there will be some small amount of performance reduction, but not enough to notice for street use. If you're getting fuel for free...go for it. When you're out for some "sporty" driving, fill up with premium.

 

Does anyone know when the computer will readjust the timing if you do move up in octane?

 

You PA guys are getting screwed big time, then! I travel around the country a lot for work, and most places, it's 20-25 cents more.

 

Hmm wonder whats worse.. getting screwed .55 cents or not having it period... good luck finding 93 in CA. - Most you will find is 91 and IT is usually 20-50 cents more (yea depends what neck of the woods you are in) - Drive around areas where most cars being driven are 91 octane or higher and youll find gas stations gouging the premium