Ignition timing and fuel octane

[jazzdude]

I have my car set up at 32 deg at 4k rpm as it seems to idle and run better at low speeds and was also continuing to run it with 95 ron fuel.

Even with new plugs and leads, I felt a very slight flat spot or mild hesitation at around 2.8 - 3k rpm when accelerating, that in order to keep the rate of acceleration constant needed just a little more throttle to push through.

I thought I'd try a higher octane fuel at the last fill up and it seems that the flat spot to not be there when I switch to 98 ron and acceleration feels more linear again. This on a 14 CUX car.

To those who have played around with maps and advance settings on their aftermarket ecus, at which point is the ignition advance a factor where it actually has to run on higher octane fuel ?

I know many on here swear that their cars run better on optimax or whatever brand higher octane fuel, even on standard cars running lower advance but there are also many who do not think that the ron rating makes any difference whatsoever to how their cars run, with these low compression engines.

[ianwayne]

From personal experience, my Chimaera 500 in 2001/02 used to pink when using standard unleaded. I used Shell Optimax (I think it was called that in 2002).

My last Chimaera 400 in 2013-17 ran OK on either but definitely seemed to be slightly better on 98 RON. My current Chimaera has an aftermarket Canems ECU and seems to run the same on either. I'm unsure if it was mapped to run on standard unleaded.

[Classic Chim]

My car running MBE was mapped on hi octane fuel. Shell I think Powers like to use. .
I was told it can run on 95 Ron as long as it’s not revved aggressively.
On a daily basis it’s hard to detect a difference but on 99 it does feel more urgent and maybe slightly more responsive.

[jazzdude]

'Slightly more responsive' describes how my car feels on 98 ron too.