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It's a rainy Sunday and I've just been doing some archive reading to get smarter about my 86 5kTQ, which I've owned since almost new (got it with 8000 miles). It now has 105k miles. As long as I have owned this car, I have been puzzled about two topics:
1. Fuel octane. The owners and Bentley manuals suggest 91 (CLC) octane, but that 87 is OK if you are willing to suffer lower performance. Over the past 10+ years, I have tried every possible combination of fuels, and have never seen any lower performance (or fuel economy) from using the 87 octane (I have compulsively recorded 95%+ of the fuel purchases). This experience has included a range of temperatures, loads, and altitudes. As a validation of this empirical data, the max. boost (1.3 bar) is the same with 87 or 91/92. If the computer were to decide that it does not like 87, I think the first thing that it would do would be to cut the boost (e.g., to 1.1 or 1.2) to control pre-ignition. Since it does not do this, it must be happy with 87. Which leads to the second question ........
2. Boost pressure. The highest (and commonly seen) boost pressure on the display is 1.3 bar. Is this normal (for a stock vehicle)?
Jeff Witwer, Director
1975 El Camino Real West
Mountain View, CA 94040