i dont fill my car in all the time.. sometimes the old man would fill it up.. i only fill up 98 octane and where possible.. 100 octane.. but my old man only fills up the cheap stuff.. 91.. at first.. i did not know or bothered to ask him what he filled my car up with.. but i do realise the engine is running abit different.. and then i realised it was the cheaper stuff.. i find the engine is alot more harder and noisier when using the cheaper stuff..