In recent weeks, out of sheer excitment that I'm able to fill up my tank without spending $75+, I've been using regular unleaded instead of premium.

I've ALWAYS used premium in the past, but lately the gap between the two has been $0.25 to $0.40/gal here in the Detroit area. I just wanted to minimize my pain and suffering at the pump, that's all. I actually filled up from below the slash for less than $31 last week!

Anyway - I had learned previously that no real harm is done to the engine by burning regular in our cars. Is this really the case? Because I've run the mileage numbers. Yes the mpg suffers burning regular. I've managed to average 19.5mpg on regular while I used to get about 21.5mpg on premium. And over the life of a tank of gas, that's only about 26.5 miles further on premium than regular.

So my point is this, if it's not doing any real harm to my engine (nothing that an occassional fuel treatment won't clean up) I'm perfectly willing to take the 26 mile-per-tank hit. Because I'm actually saving more money than that 26 mile loss is costing me.

BUT...If someone has got evidence - or even some sound knowledge - that burning regular does real harm (other than fuel effeciency and performance losses), then I'll certainly reconsider my conclusion.

 

If your compression is high enough (I don't know the stock compression on a sc400) it can cause knocking.

 

Dude why did you have to post another gas thread JESUS! It does cause cylinder wall and piston damage because that spark knock is early detonations. The detonations can happen between strokes causing your car to under perform. You also run a chance of setting a check engine light. You ECU can retard the timing so much to avoid that detonation ,but if it notices enough knock/ping threw the knock senor the light will go off.Your computer ends up dumping more gas to prevent the knock/ping condition so your using more. Gas isn't $4 or more your seriously going to be that cheap. If your doing that you might as well be driving a Toyota Corolla.lol