OK, I'll bite - what does summer time have to do with running higher octane?

 

He's probably referring to air density, but once again, the computers account for that type of stuff...
http://www.racecarbook.com/articles/airdensity.shtml

 

I have always run 91 in my Ram. At 7000ft it has the equiv rating to meet my 93 octane requirements. However, I agree that you can run 87 if you prefer without worrying about it (stock). I am also an enghinear.

 

Outside Air Temperature OAT Hot air into an engine will promote pinging or preignition with a low octane fuel, Cool or cold air into the engine with low octane may offset the tendency to preignite or aka ping, Higher octane in the hotter days just makes better sense, i know computer adjust for all these situations, i know if we could use e85 in our Hemis they would make more power and even more with a programmer.

 

I think too much is assumed that the computers adjust to. It will and can adjust for spark knock immediately. There is a reason higher octane is preferred. This same argument is on the corvette forum. A FEW insist that 87 is OK. Selective reading. That is NOT what is in the owners manual.

 

you know what they say about assuming...

i agree with what Hammer says. "89 is about a $4 per tank insurance policy IMO." if you fill up once a week running 89 would only cost you about $208 more per year. now how much would if cost you to replace your engine if it was to fail prematurely due to you running lower octane gas?

 

This is what my C5 vette manual says - Use premium unleaded gasoline with a posted octane of 91 or higher for best performance. You may also use middle grade or regular unleaded gasoline rated at 87 octane or higher, but your vehicle’s acceleration may be slightly reduced. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it is bad enough, it can damage your engine.

Let's keep the discussion about gen 4 hemi engines. Also, I will remind you that since you tested knock detectors over 20 years ago, the technology has changed a lot in regard to microprocessor speeds and memory and how an engine can be controlled not to ping. The drive by wire has it's own calibration curves, the short or long runner selection also contributes, the air pressure and density detectors as well as the variable valve timing of the gen 4 makes it a lot more complicated to control pre-detonation than just retarding the timing. You would be surprised how much stuff is recorded in memory and used to control modern engines.

 

I was just stating the same type thread with a member stating that his C6 vette runs just fine on 87 octane is being discussed on that forum. He said his manual said it was 'acceptable' I did not look in my manual. As far as microprocessors what I know is that I hear late model Suvs pulling off at intersections faintly spark knock then self corrected. Do you have a clue to just how far these microprocessor's can retard the timing? What is the parameters? There is a reason the manual says 89 preferred! Maybe,just maybe the computer can only retard or advance in a short parameter. If thats the case then too low of a octane is detrimental and thats the reason the 89 is the prefered octane.