AO Silver Member
Join Date: Nov 2003
Location: United Kingdom
County: Perth and Kinross
Re: Premium fuel, an advantage or gimmick?
There are a few people on here who know what they're talking about. Unfortunately, there is still some misinformation. Let me explain a bit.
Higher octane petrol burns more slowly than lower octane. This is why when unleaded started to replace 4 star, ignitions needed retarding to prevent pinking (pre-ignition). Only the very latest performance cars will advance the ignition to run with high octane. 155s and 156s (any 16v Twinspark engine) can only retard the ignition from standard. They're map is only optimised for 95 octane. They need a remap to make best use of high octane.
Any petrol engine should run smoother with high octane. It burns slower and exerts a more sustained pressure on the piston crowns. It is kinder to the engine. It has a greater anti knock ability so more ignition advance can be used. Calorific value is about the same in 95and 98 octane.
High octane fuel using methyl alcohol actually has a lower calorific value. It still has a greater anti knock effect, so the engine can produce more power although the fuel produces less energy. As already stated, methyl alcohol needs a richer mixture. Supermarket high octane has methyl alcohol (5-10%). It is cheaper, but the lambda sensor will slightly increase the fuel quantity to suit. Therefore, branded high octane is probably more cost effective IMHO. An older car with no lambda will run a little weak with this fuel and the performance benefit will be slight if any. The combustion chambers will also be hotter with methyl alcohol.
Some cars such as Subarus will run worse after a service because the knock sensor will detect the vibration before the new oil filter is fully primed. It will retard the ignition for up to 2 hundred miles.
In short, if you want you're TS or V6 to have more performance and run smoother, use either proper (not alcohol) branded high octane, or a booster, and have it remaped to suit.
AFAIK, Esso only has 97 octane whereas is 98 and V-Power 98.6. That is why BP and Shell tend to give better results. That said, closed loop managemet systems have been known to give good results with 99 octane Tesco, although fuel consumption may be greater.
[SIGPIC][/SIGPIC]Drive sideways- life's too short not to
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