So a question about Shell - or any Top Tier gasoline retailer: is *all* the gas they sell Top Tier?
Short answer: With regard to Shell gasoline, yes, all grades/octanes are Top Tier rated based on the level of detergent properties per milliliter.
In this regard, the question that always comes up is whether there are more detergents in higher octane Top Tier gasolines. Again, the answer is yes.
To find out how much more and how various fuels differed, last year one of the news services (ABC?) asked/paid Paragon Labs to test several of the TT fuels, including Exxon-Mobil (XOM), Shell (RDS), British Petroleum (BP) and four or five others. Among regular grades of fuel, those three came out on top (which is why I remember them), and they were comparable (approximately 15 milligrams of additives per milliliter). When it came to the higher octanes however, RDS had twice the detergent properties in their 91 octane fuel (31 mg/ml), and roughly 18% more than their next competitor, XOM (31 mg/ml for RDS vs. 26mg/ml for XOM). Shell also has a unique additive, nitrogen, which independent testing has determined more readily combines with carbon atoms during the combustion process. The result is a cleaner burning fuel.
This, of course, begs the question as to whether there are any other reasons to use 91 (or higher) octane fuel. This has been debated here endlessly. However, FWIW, if you are familiar with how Honda's engine control module (ECM) works, you know that
within a narrow range (and that's important), the EMU will advance and retard the ignition in response to "pinging" (that rattling sound you hear when an engine is lugged) or the absence of it. In other words, if you consistently use a higher octane fuel, the ECM will respond to the absence of detonation, and advance the timing
slightly within the fixed parameters of the EMU. Thus, the engine performs better, and you can get
slightly better mileage. Whether that slight improvement and the additional additives are worth the additional cost is, of course, entirely up to you as an educated consumer.
