Fuel

From Celica GT-Four / Alltrac - ST165 ST185 and ST205

Fuels for the GT-Four

There are many fuels available for cars these days, and these vary from country to country, company to company as well as from station to station. There are things to note when choosing your fuel, mostly based around the target market of your car:

JDM cars are designed to be run in japan where 100 RON (UK) fuel is the norm. They have advanced timing curves to take advantage of that. They should NOT be fed supermarket/low RON fuel, even if they are not modified. They will suffer knock/detonation (most likely to be inaudible to the human ear) and this causes engine damage either progressively or sometimes catastrophically. If you have a JDM car in the UK only put Optimax, V-Power or an equivelent premium fuel into it - these have 99+ RON and are as close to the Japanese fuel they were designed to use as possible.

USDM cars are designed to be run with very poor quality fuel that was available at the time. These can be run on just about any petrol you can put in them.

Export - these are UK cars and European cars - "all other". They are mapped for 95 RON fuel, they will accept any UK fuel but prefer premium. All fuel loses its RON rating with age, if you buy 95 from a small garage that doesnt sell it often you could well get an old batch and have something closer to 93 or lower.

These cars have a knock sensor but it is there as a damage limitation device, NOT a closed loop system. It doesnt advance the timing until knock is detected - it starts with the set mapped value and then adjusts the timing trims depending on where it sees knock. If you want the best possible timing levels from your ECU - reset it with a full tank of v-power. But bear in mind that the ECU is ALWAYS learning - if it detects knock due to a batch of supermarket fuel you threw in to get you from home it will hold that low timing value even if you put the expensive fuel in next time - you will need to reset the ECU after using cheap fuel.

DO NOT reset the ecu too often, the process of learning the knock-limits for the timing requires, naturally, knock to occur. This is damaging. If you reset the ecu every week you are punishing your engine weekly. The ECU was designed to be reset very rarely, only when an error is detected or the battery goes flat.