just stick with the 87

 

I tried 87 in my last tank. Didn't really notice a difference other than maybe slightly less MPG. I've just always used 93, but in my last 2 daily drivers I've used 89 (a Chrysler Concorde LXi 3.5L and now the H3)

 

Well i started using 89 octang it seems to run better.

 

Not to discredit any of your thinking about what you believe is the best octane level for this H3 engine...Based on the R+M/2 octane rating equation for all USA and NA engines.

But in today's modern gasoline engines as well as this H3's Low compression engine, the onboard engine management computer (ECU) monitors the engine for any predetonation and adjusts the timing accordingly..The baseline setting is optimally set for 87 Octane...If you were to use the slower burning 92+ octane you are pissing away your money needlessly and also carboning up your engine, so otherwise you're just fooling yourself...The more you use this higher octane fuel the more the carbon build up will become and eventually you will NEED to burn it as the compression ratio will have increased and the ECU adjustment will no long be able to control predetonation as it will be outside it's window of tolerance for control...The Best thing is to use 87 octane and no lower, unless you hear any pinging at higher altitudes under load, then step up to 89 octane...89 octane is produced by blending at the pumps the only two sources from the two underground storage tanks of the Station, the 87 and the 92+.

Hope this sheds some light on this age old confusion[sm=shades.gif]