Hi,

WRX STi Spec D 07/07.

It says on the inside of my filler cap to use 98 RON. I've never seen 98, only 97.

Is 98 RON a fuel they use in Japan?

I run mine on Esso 97 RON and had no problems. Is Shell Vpower 99?

My old 54 plate WRX STi UK blob with PPP ran better on 97 than 99 I always found. The 99 would seem to alter how it ran, almost like the timing was slightly out.
This was 5 years ago, and I remember Tesco 99 RON being 99p a litre lol.

 

It's use 98ron or above so use Shell V-power 99ron or Tesco Momentum 99ron.

 

If you read your handbook I'm sure it says you can use 95ron if 98 is not available, though I wouldn't myself.

 

Ive read a few threads like this generally every one says try to stick to v power or tescos 99 and try to avoid 95 if possible

 

On my recent trip to south of france i noticed that i could only get 98 over there where ever i went.

 

Filled up tonight with Shell V Power. Feels smoother running it on that rather than the 97 RON.

I can't see any change on the water temp guage, but would then engine run hotter or perhaps cooler with 99 instead of 97?

 

I doubt you would notice any temp changes, Give it a couple of days for your ecu to re-learn because you have higher octane fuel and you may get a few more horses. It should stop your ecu from retarding the ignition if it were detecting det on 97ron which would cost some power.

 

What is det?

 

Detonation in the cylinders

http://www.thor-racing.co.uk/Detonation_or_Knock-36.asp

 

Detonation. It where the fuel starts to explode under compression before its ignition time. It results is serious engine damage, very quickly sometimes. The higher ron fuel is more resistant to detonation.