I am currently running a MY94 STI Import, It's been de-cated, plus other mods, runs about 280-300BHP, I was using Shell Optimax which Is a 98 Ron fuel, but my local garage changed franchise and the nearest Shell shop Is over 20 miles away!! Would I need to boost the octane to 98 RON If say I'm using BP ultimate which Is 97 or would the car be fine on the BP juice?

 

Stick in some NF Race and your engine will love you
http://www.nfeurope.com/index.htm

 

Boosting your octance is not essential.... but in the long run can cause damage to your engine.

I have a STi Ver3 import and have always ran it on Optimx which is sufficient, as hav the previous owners to my scoob.

Using normal 95ron or the BP will not really affect your car short term.

I know some1 with a a STi v2 import and he has neva used octance boosters and 95ron fuel- no problems...

...but others have had engine meltdown.

In a nutshell.... BP is fine. now and again treat her to Millers or as has been said NF octane booster

 

I dont think octane booster is something that you add now and again. Too low an octane rating results in detonation and ultimately engine failure. If you are going to use it, then use it all the time.

Get a knocklink and check for any det that may be occuring with the lower octane fuels. If you dont get it with 97 RON then you should be ok, but there are no garauntees.

A remap is always best.

Just for you info, I run an MY98 WRX with Optimax and Millers. No det.

 

I'm sorry, but this information is wrong.

95 octane is NOT ok on an import unless you are pootling around. Start using the car to its full potential on 95 and quite soon you will be looking at a rebuild.

We get literally dozens of imports which have blown engines purely and simply due to insufficient fuel octane being run particularly at high motorway speeds (e.g. "I was racing this M3 when suddenly....). The cars are mapped to 100RON so to say that 95 is fine is ludicrous. If certain people are prepared to risk it on their own engines, then thats' up to them, but I certainly wouldn't advise it as a general practice.

Yes you may get away with running them on Optimax in the same way that you may get away with smoking for 10 years without getting cancer, but that doesn't mean there isn't a risk, and being as the average rebuild costs £1500+, it's quite a gamble to take. If you are a hard driver (especially if you regularly venture into the 120+mph territory) then you are taking a serious risk running an import on just plain Optimax. If you aren't a hard driver then fair enough, chances are you could get away with it.

Also, using octane booster "occasionally" is a complete waste of time and money unless say, you put it in for a trackday for example, where the car WILL be driven exceptionally hard. Your ECU won't know whether it's coming or going.

Not having a go here, just trying to prevent even more import engine expiries (so I'm actually doing myself out of a job by posting this)