Well my theory that octane was significantly affecting mileage may be dying. Got a good 100+ miles of freeway cruise at 70 or so on it yesterday and today. That brought my <13 mpg upto 15+(which is in the ballpark of my mixed commute and freeway average). so now I doubt that the computer is retarding the advance into the toilet which would cause poor mileage. I think the commute is the major factor now in my wide swings in mileage.
I am leaning more and more to the theory that my commute being less than 10 miles one way the engine really doesn't warm up. If all I have is commute miles, the mileage is lousy. As I get more freeway miles the mileage becomes acceptable for mixed driving but short trips. I have not yet had a chance to do a full tank full at freeway speed. I really need to make one of my I5 LA to Portland and back runs with different octane. That should tell quite a bit.
Interesting that my old 96 SS had 10.5 compression and the factory recommended 87 octane and I never, ever had any problems no matter what kind of driving I did. Strange that Ford couldn't do the same with a newer technolgy engine. The LT1 had reverse flow cooling and that was claimed to be a big part of running regular at 10.5 compression, that, along with computer knock control. I am guessing the LS engine is more stressed and high strung and so more sensitive to octane. Oh well apples and oranges.
I do know that 87 will ping under load with the LS and if you punch it, the engine may even stumble, so definitely not adequate fuel for the LS. 89 appears to be about the minimum in my driving "experiments" that doesn't have any audible or "driver feel" symptoms of ping. I am sure the computer is running up and down the advance curve tho, as that is it's job. May have to work harder on 89.
Again THe LS vs SHO vs SS is apples to oranges to watermelon comparison so you really can't read too much into the following... The 89 V6 SHO is what I had and I think it was 10.0 or more compression if I recall correctly. The Car and Driver article( SHO CLUB reprint...
http://www.shoclub.com/ goto SHO History) printed in 92(maybe out of date thinking?) essentially said the Ford engineers tested the V6 and...
>>>Some cars benefit from fuel higher in octane than the 87 PON (pump octane number) of regular unleaded. But not many. In fact, one of the most exotic engines on the market today runs happily on regular: the 24-valve V-6 in the Taurus SHO. Above 3600 rpm, it delivers its full output on 87 PON gasoline. Premium and super premium add nothing but gravy for the oil companies.
Ford recommends premium fuel for the SHO V-6( they also Recommend it for the LS, my notes). It’s plainly a high-performance engine, and Ford decided upon premium way back in the concept stage to avoid design constraints on power out put. But when the job was finished, the resulting engine worked fine on regular fuel, primarily because modern engine technology eliminates the bungling operation that, in past engines, could only be smoothed over by high-octane fuel.... If your engine doesn't ping on regular, premium will do nothing for you. Moreover, most engine engineers will tell you that a modest amount of part-throttle ping bothers you more than it hurts the engine.
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I do not totally agree with the article since it said the Ford engineers claimed it never pinged. I did hear ping on maybe a 4%, long hill, hot day and AC on, so summer time I went to 91 or even 89, if I was being cheap, The rest of the year 87 made no noises. I drove my SHO 120K miles without problems in the engine itself, and I was rarely gentle, that engine liked to wing it. The rest of the mechanicals were a well known issue tho. So I sold it. I have seen similar articles from time to time in various rags, so I assume there is some truth to it but may not apply on our LS engines. And of course don't believe everything you read.
More experimenting to do, I only have maybe 5K under the belt with the LS so lots to learn yet. Man I miss my totalled SS, it was so unfussy, but I also experimented in devious ways with it too.
Jim Henderson