So I've got my Spec-D back on the road after a couple years sitting. All smiles back on my face especially when hitting the silly pedal! This was until i realised they had demolished my local Shell garage so I now have a 35 mile drive just to get V-Power. The car has only ever been run on V-Power since its ECUtek road mapping session. Nothing drastic in the map just a fast road map on V-Power and a less aggressive one as an option.
The nearest highest RON fuel now is Tesco 99. Question to those in the know on the ECUtek is whether switching to Tesco from V-Power will cause any noticeable difference or issues. I was lead to believe if i put 97 through it at any point the ECUTek map would need to 're-learn' via a tank of V-power before giving me peak performance. No issue driving 35 miles if needed but would be nice to know if i get caught short.

 

no it wont learn, if you have to put as small a quantity of 97 in as you can get away with, drive it off boost and under 3500rpm and drive to a shell, full tank to the brim, drive it steady for that tank as its a partial mix, then let it drop as low as you dare and refill to the brim.

dont forget tesco 99 as well is an option.

 

My sti blob is mapped for v power,however I regularly use Tesco super ul,no issues at all..iirc v power is 99.3 Ron and Tesco is 99.0,pretty sure 0.3 will make no difference for road use
tesco usually a bit cheaper aswell��

 

The Octane number in itself is not the most important factor , I mapped with Duncan at SRR on Aral 102 which I brought over from Germany , but I subsequently found I had to frequently use Hessol Super plus ( which is Aral 98 ) ,
thankfully both have some antiknock additives, but the power loss is really noticeable. The Map does not relearn for lower Octane , but it does pull the timing back if it see's a knock event. I would say you should
avoid this on a standard WRX build at all costs. Sti pistons are a bit better but its still playing roulette.

My latest block is forged and the build cost 4k€ and although my Mahle's will deal with a mix in of some 98 octane , but I do hate the loss of timing so much that I do carry a 102 Oktane 5 liter can around
so that I don't have to compromise. If you value your engine life the fuel cost delta is irrelevant.

Tidgy has it nailed when he notes that you can drive on the lower octane ( off boost ) , If I must , I keep under 3800 / under 0,5 bar but it can be very tricky if you live on a hill.

 

Guys sorry for a late to reply to this but thanks all for clarifying. I think i’ll play safe and learn to plan to enjoy the drive over and back to the Shell for now.
If I get caught short i’ll get go the Tesco 99 route. Tempting to see if I can feel the difference at all. I was also concerned about the additive element for knock issues with Tesco 99 vs V-power but sounds like I may not need to worry as much as I do.
Really painful to drive off boost for any time... I remember the 1000 mile run in time after forge work sucked.... no one likes to cage the beast