My local Esso garage has just started selling 99 Octane petrol. This has made me think about how much of a “high performance” engine the X Wedge really is. S&S say it’s a high performance engine and it should be fuelled with minimum 96 RON but in the grand scheme of things 80ish HP from a 2 litre isn’t huge although the torque is impressive. I wonder how much benefit better pre ignition control through higher octane fuel will be for this engine given it has a knock sensor and presumably the programming to exploit it? Anyway assuming that the ECU would be doing less retarding I filled up with it anyway but discounted what I perceived to be a crisper performance as probably placebo effect.
My engine hasn’t been upgraded apart from a better intake filter, has anyone run a M3W on higher octane fuel say 99 vs 96 RON on a dynamometer and shared results? I imagine those that have done engine upgrades will know more about this than me.
My Uncle very many years ago always insisted on using the most expensive, highest octane petrol he could find. I explained to him the higher lead content made it burn slower to suit higher compression engines only and reduce pre ignition but my warnings fell on deaf ears despite the modest cars he drove.
Having said this I did need to use 5 star (101 octane) when it existed in the 70/80's in my Jensen CV8 as that had a 10.5:1 c/r and would pink on anything less. I currently also use premium in my 1960 Velocette for same reason.
The X wedge in the M3W has knock sensors though and will run fine on regular. I never used anything else in my Stage 1 car. It has been suggested you might get slightly better fuel mileage with premium but not enough to compensate for extra cost.
