Some recent cars have the ability to advance the timing until the computer detects a knock (some Fords do this I believe), and could theoretically benefit from higher octane than recommended. But most don’t and I don’t know how well this actually works in real world use.
On most cars if you are going beyond what is recommended, the engine can’t make any better use of the higher octane, and since adding extra volatiles such as alcohol, that have less of an energy content is what increases the octane, you will normally get a little less mileage out of the same quantity of fuel.
Some recent cars have the ability to advance the timing until the computer detects a knock (some Fords do this I believe), and could theoretically benefit from higher octane than recommended. But most don't and I don't know how well this actually works in real world use.
Even without detonation, you can have more spark advance than is optimum. The high octane fuel allows a high compression engine to use that optimum spark advance. Low octane fuels must use a less than optimum spark advance in order not to detonate.
Regarding the use of premium gas in a regular gas engine, and what effect it might have, don’t forget about the power of suggestion!
The father of one of my friends from many years ago was an engineer, and he drove a VW bug. This man stated that, after accidentally putting premium gas into the VW’s tank, “it had incredible power”.
If an engineer who should have known better was prone to that type of delusion, just imagine what a non-technical person might imagine after filling his tank with high-octane gas.
Now that premium is now $0.40 more than regular around here, I could use that money on a bottle of Techron instead and come out ahead, both in $ and in cleaning benefit.
What hasn’t been mentioned is that detonation, a.k.a. spark knock, is affected by intake air temp.
Regular 87 octane is spec’d for my 2006 Matrix.
However, I find that engine response is a bit sluggish when the ambient rises above 90F, even accounting for AC compressor drag.
I believe that’s because the knock sensor kicks in and starts to retard timing.
As a test I ran a tank of 89 octane during a heat wave and found an improvement.
There was no noticeable change in MPG.
AFter doing some checking there is ONE gas station on NH that sells ethanol free gas. It’s in Freedom NH. I could drive there and buy the gas…but by the time I got home I’d have to turn around again to fill up. There are no stations in MA that sell ethanol free gas.
One of my cars requires premium. I have never gotten stale gas and I’ve owned it for 8 years now.
That said, the others are right. There is absolutely no reason to put premium in your car unless it says premium is recommended or required, and plenty of reasons not to.
I certainly wasn’t offended, I thought you wold like the correct information, that’s all. Mexico or Western Virginia seem like fine places to me. I spent time in Cozumel, but nowhere else in Mexico. But the people we met seemed a lot like us.
With 10:1 compression I don’t think it’s delusional to think this engine could knock at optimum timing with 87 gas in some situations.
My motorcycle engine has a 10.6:1 compression ratio and not only is 87 recommended by the manufacturer, but I have yet to detect any detonation while using it.
Of course, the compression doesn’t actually start until the intake valve is closed and the cam timing on this bike has the intake valves closing at 56 degrees after bottom dead center.
The Prius engine has a 13:1 compression ratio but it never uses the entire stroke to compress the fuel air mixture. The intake valve stays open during the first part of the compression stroke allowing part of the air fuel mix to return to the intake manifold. It also runs on 87. The engine most likely has an effective compression ratio on the order of 8:1 or so, with a 13:1 expansion ratio during the power stroke.
circuitsmith
@b.l.e. what's your point? I am delusional? Maybe I shouldn't be here...
No, I was simply explaining why engines with high compression ratios can still burn 87 octane gas. There's more to it than the nominal compression ratio.
Back when two stroke engines were popular in motorcycles, the Japanese listed the “corrected” compression ratios while the Europeans listed the “nominal” compression ratio. The corrected compression ratio was calculated by the volume of the cylinder above the ports, the nominal compression ratio counted the entire piston stroke. This meant the Japanese bikes had compression ratios on the order of 6:1 while the European bikes had 10:1 ratios. They measured their compression ratios differently.
Engines can have a high nominal compression ratio yet have a low effective compression ratio.
My reply wasn’t about you, I was just using your post to bring up this point.