I've done it over a full tank of highway miles and it was fine but I was just cruising the whole time. Didn't see a hit on mpg.Just wonder how the performance and gas mileage are affected.
Required fuel is regular unleaded with premium recommended. So using regular fuel won't void the warranty, but it'll pull timing and cut power to adjust for the different fuel. Basically with the Si (and Type R), the engine is designed to run on premium, but can run on regular as well with an ECU that will adjust timing for the fuel that is in it.Just my two cents..Honda recommends premium in the turbocharged Si for a reason. I would never recommend putting regular in a car that is designed to run on premium fuel unless you want to risk some type of future repair work. Also, I'm pretty sure it says either premium fuel only/required or at the very minimum, recommended right inside the fuel door as a reminder. I'd also think this could potentially void the warranty on the engine should something go wrong from running 87.
They definitely won't void the warranty for using regular. It says premium recommended.Just my two cents..Honda recommends premium in the turbocharged Si for a reason. I would never recommend putting regular in a car that is designed to run on premium fuel unless you want to risk some type of future repair work. Also, I'm pretty sure it says either premium fuel only/required or at the very minimum, recommended right inside the fuel door as a reminder. I'd also think this could potentially void the warranty on the engine should something go wrong from running 87.