BP Ultimate in the Aygo Tank

[Planemo]

I was under the impression we were talking about a definitive engine though.. never mind.

[Justhandguns]

20 hours ago, Planemo said:

EGT, lambda, detonation, pre-ignition, power, torque and many other parameters can all be monitored and data logged on decent dynos. I have done much of this work myself in the past. I am aware of the Aygo engine, it's type and method of engine management. I have also seen time and time again, many results of supermarket fuels, in front of my own eyes, on the dyno. They were nearly always poorer than a 'branded' fuel. We used BP by default as it was consistent and gave reliable data but I am not saying that Esso or Shell are any worse/better. Supermarket fuels, at best, were never as good as something like BP. This is due to a combination of factors - additive quality or type of octane booster used (as already stated ) or even how long they have been standing in the refinery (octane drops to a noticeable extent over time).

 

Absolutely agree, there is certainly a quality difference between branded fuels and supermarket fuels. Remember the Tesco fiasco? Maybe they come from the same refinery but there is always a difference between how they handle or store the fuels. My dad used to use just one single brand of petrol for our old car. But at the end of the day, most of us would probably go for the nearest or the cheapest pumps available. 

Besides from the price/RON/addictive factors, Planemo also brought out another thing which we should be aware of, how they store their stocks. Fuel does go stale due to the moisture absorbed from air and the oxidation of the fuel itself. So it is better to use a busy petrol station where the supply is always fresh. 

I also don't buy the notion of engine overheating using high RON petrol, otherwise cars in places like Hong Kong would have blown up big time. Their standard unleaded has a RON of 98.... 

[Planemo]

Very true, same with Japan - 98 is the primary fuel which is why even stock engined imported Imprezas etc will detonate on 95. It caused a few issues over here when they first started bringing them over as 98 was quite hard to find here in those days. The modified ones were even more of a problem when they were brought over - people had to find 98 and then religiously add octane booster additive on top of that. It wasn't until tuning companies like the one I worked for were able to re-map/fit standalone ECU's that we managed to map the cars a little more conservatively and allow the owners to run on straight 98.

Higher RON simply reduces the point at which the fuel will ignite, hence it's use to prevent pre-ignition/detonation. The suggestion that it will overheat engines is a total myth, brought about simply by folks who believe that 'higher RON' = 'bigger bang' = 'more heat'.

Start looking at fancy fuels like nitromethane and methanol and you will find that they are incredibly hard to ignite, which is why they are used in race/drag cars. It allows for massive compression ratios, crazy igntion timing and huge turbo/supercharger pressures before the sparkplug actually ignites the mixture. I accept that these fuels are slightly different to petrol in terms of how they combust (a whole new topic) but the fact remains that racers strive to get the highest octane possible in order to PREVENT combustion. Trying to get a top fuel engine to not act like a diesel is actually the Holy Grail.