When I picked up my car from its big service the other week, it seemed to be running pretty good. I dropped of the car at the garge with the fuel tank almost empty, but when I picked it up I noticed that there was a bit more fuel in the tank, so I presume that Jorrit had topped it up a bit (I'm sure I'll find out when I receive the bill, since he will undoubtedly charge me for it).
I think Jorrit uses either Texaco or Total fuels... mainly because he has a discount card for his local petrol station, but also because they offer 98 RON in the Netherlands. For various reasons, I've been using Shell fuels. Until about a year ago, Shell also offered 98 RON fuels in their petrol stations, but this has since been phased out and replaced with V-Power. V-Power is 95 RON in the Netherlands and as far as 95 RON petrol goes, I have no reason to believe that it's no good. In fact, I have a bit of insider knowledge so I know that it's better than 95 RON fuel and it's also better utilising our hydrocarbon resources (but I won't go into that here).
Since Jorrit only put a splash of fuel into my car, I've since refueled on V-Power. Not long after doing so, the car seemed to feel a bit flatter... a bit less responsive. Also, if I think back to the recent dyno runs carried out with my car, they've been with 95 RON V-Power rather than the 98 RON fuel that I used to use. So I'm starting to think that using 95 RON V-Power in my car is not the best. High octane fuel offers resistance to engine knock, as you can read about on Wikipedia. What I've seen on recent dyno runs is that my car is running very rich. A rich mixture may be symptomatic of a poor setup, but it can also indicate that the engine management system is detecting some engine knock.
If the engine management system detects knock it can do a number of things. It can retard the spark or it can increase the air/fuel mixture, making the engine run rich. I have a strong suspision that when I run 95 RON V-Power in my car I loose power... the car feels more sluggish and on the dyno it seems to run rich. I'm therefore going to try running on 98 RON fuel for a while (maybe try out BP Ultimate) and see how it feels before taking the car back to the dyno. It will be really interesting to see if there's a difference in output between the different fuels. Given that my Ghibli runs with a decent amount of boost and that the intercoolers are not as effective as they could be (i.e. the charge is both high pressure and high temperature, both of which increase the tendency for knocking), I suspect that the fuel's octane rating could have a significant effect on the engine's output, maybe as much as 10-20hp?
I'll keep you posted on the results!
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