The method I read was that the 95 was Research Method (The R in (R+M)/2). It apparently yields a higher number than the M method. I just read that the equivalent octane rating if were listed as current octane levels are would be about 91 octane.

Originally posted by mcarter Simplify maybe. I have vintage vehicles that run on premium and need a lead additive.

I think you would be fine. The single octane they are talking about is 95 octane (they weren't clear on the method). There may be things you will have to deal with the lead issue. Likewise, the ethanol will be an issue for seals and such.

You can always go to an airport and get some 100LL....

As for my nail bags, their demise relates to high humidity condition in the basement of my house in NJ.  It rotted them.  I had another pair that I bought in 1966 that lasted over 40 years.  I'm getting a new pair from Kline Tools like the old ones.  They should last until I'm 100, if I last that long, especially working on the top of patio roofs.

Seriously, though, do you have some reason to disagree with what the Ford and Chrysler folks have published?  

They don't talk about high altitude 84 or 85 octane and don't state what they mean by "normal conditions" nor "some circumstances."  They do warn against allowing heavy spark knock at high speeds and suggest that it indicates service on the engine is needed.

So the the dilemma persists.  Should one buy 87 in "high altitude" states where they sell 84 or 85 octane gas?  

As for premium grade gas, looks like the Chrysler 4.7L, naturally aspirated engines don't drink it, though it'd be nice if they would clear up their ambiguities on the topic.  Seems to me the best source of octane information is the engine maker, since it knows what the engine design parameters are.

You really do need to pay attention to the requirements of the engine. For example, the F-150 has four engine options. Two are normally aspirated (or NA); the 3.5L V6 and the 5.0L V8. Two are turbocharged (EcoBoost); the 2.7L V6 and the 3.5L V6. They all accept 87 octane fuel under normal conditions. However, the turbocharged models recommend higher octane for "severe duty", and specifically call out towing as an example.

In both UT and CO they were using the (R+M)/2 method as is pretty standard in most places I've been.  Thus, my dilema continues. 

I think next time I'll just buy the gas without ethanol.  What I need is an anemometer with a constant graph print out to measure the varying wind velocities, then compare the mileage with the wind factored in.  On second thought, I think I'll just keep cruising along and go slower when I need to.  Eventually, we'll arrive..... somewhere at any rate.   

As for the grading method, it was the (R+M)/2 at all the pumps we visited on our trip.