Ok so anything with a compressor(turbo or supercharged) which increase conpression ratio should always be run on high octane gas. Same with most motorcycles because of high compression.
New cars have knock sensors so you wont ruin your engine if you run low compression, but the timing change will probably affect gas mileage more than the price of premium would cost.
And the guys with the rx-8’s, if your wankel motor knocks one time it will be done for, Ive witnessed it on a rx7.
The discussion seems to ignore the relation of ignition timing to fuel octane (“regular” is lower octane than “premium”). Higher octane gas burns slower than lower octane and therefore requires the spark earlier in the cycle.
If you switch from regular to premium, the spark must be advanced to match. If your car has computerized ignition timing (ECU) and vibration (“knock”) sensors, then the software will SLOWLY seek more advanced settings after you switch to premium. The first few tankfulls may actually get worse mileage, but eventually the correct timing will be achieved and then you can tell if premium gives better performance or mileage.
The timing software algorithm behaves like the blind man warming his hands by a stove every morning. Then someone moves the stove further away (switch to premium and the “knock” moves further advanced in the timing spectrum). The blind man finds much less heat, but CAUTIOUSLY moves forward seeking the heat. Eventually he finds a satisfactory place and is happy again.
On the other hand, if the stove is moved closer, then the next morning he burns his hands and RAPIDLY moves away. That’s what happens in the software if you switch from premium to regular, causing immediately more vibration (maybe even knocking/pinging) and the software quickly retards the timing.
I switched to premium on my old ('87) Suzuki Samurai with manual timing adjust. Because I set the timing myself (normal tuneups when running regular and re-adjusted to a more advanced setting just as I switched to premium) I didn’t have to worry about how long it took for the correct timing to be achieved.
My results were both better mileage (enough to pay for the difference in price) and much smoother operation, especially at lower rpm where I achieve best mileage (this thing has the aerodynamics of a brick).
By the way, if you want to switch to premium to test it, and you have computerized timing with knock sensors, you can adjust he timing more quickly by disconnecting the ground lead from your battery for an hour or so to erase the computers memory regarding ignition timing. Unfortunately, this technique also may erase your radio’s settings and you should check your manual to refresh your memory about the security alarm if you have it normally turned off. It may come on when you reconnect the battery.
PS to my above post:
I think Tom and Ray have ignored the possibility of the more complete burning of the fuel when premium is used - especially in the every day road car with lower compression and operated at lower rpm normally. It’s necessary in higher compression engines, but in my slug 87 Samurai it did provide more power at all rpm’s.
Premium achieved using ethanol does have less energy per gallon, but burn efficiency can’t be ignored. I don’t pretend to have the answer in all situations, but understanding the constraints (like the ECU adjusting slowly, etc) means you can run your own more accurate experiment. I recommend keeping track of miles and gallons over at least 10 tankfuls and averaging all of it before deciding. There’s too much error in a calculation based on a single tank or even two. It might be best to buy all that gas from the same station, too.
My independent Mercedes mechanic (highly experienced and knowledgeable) says that running regular when premium is required can ruin the catalytic converters, which are about $800 to replace. Nobody loves Big Oil, but careful that you don’t cut off your nose to spite your face.
With old springs in the distributor advancer mechanism the spark advance will come on too soon and may cause more pinging.
Pinging occurs when the cylinder pressure increases suddenly (from burning fuel air mixture) before top dead center of the compression stroke instead of after (power stroke) causing the pressure to fight the motion of the piston instead of assisting it. Ask anyone who has hand cranked an engine to start it, and felt this happen, what this felt like. If we can somehow delay this moment enough we eliminate the ping. If we delay it too much we lose (waste) power.
By the way how about some discussion about direct injection in gasoline engines - in particular turbos - like Audi - allowing much higher compression ratios even with engines that sometimes have big turbo boosts?
In the winter, in my area, the pumps say 15% ethanol.
Did you read the plugs? The fuel air mixture may be too lean.
Balance has an effect too. Many of the older engines did nto have great balance in the fuel air charge that got fed into each individual cylinder. Newer engines are designed / built better.
I had a 2000 Cadillac Deville that “reecommended” 91 octane fuel. It started life as an Alamo rental car, so it had 2 chances of ever having been NEAR the high test fuel pump within the first 20,000 miles before I bought it: 1) fat and 2) slim! Consequently I ran it for the next 100,000 miles on 87 octane, topping it up with premium about once every 20,000 miles or so, out of pity for the pistons and a sense of guilt. I finally filled it from a near empty tank twice in a row with 91 octane gas at about 117,000 miles and it proceeded to blow a headgasket shortly thereafter. Coincidence? I don’t know, but just maybe all that attention and octane were just too much for it to handle! BTW, I followed all the manufacturers service recommendations faithfully, including oil changes every 3000 miles, right up to the day I traded it for a new car. And all the work was done at the Cadillac dealership where I bought it.
With our check engine light on (and cruse control disabled as a result, I was forced to go to the dealer, who found an intermintant rear oxygen sensor. “What gas have yopu been using” ‘Regular’ (it is 85 octane at high altitudes, the manual calls for 87, (regular in the rest of creation)). “Use mid-grade” (89 octane). Makes no differance. The check engine light comes on within 50 miles of resetting the computer. However, the car’s computer thinks we are getting better mileage! Time will tell if the 10 cent premium is justified by the incrementally small increase in mileage. But it is annoying to go get my weekly computer reset.
I have a Mazda Mellia non turbo the filler door says that I should use premium gas the The manual was missing when I purchased the car and have been using regular, am I damaging the engine? the car does not seem to knock
Audi 2 ltr in VW van. 10:1 compression ratio. I used 87 and a few times 89 with no change in MPG. Manual says use highest octane available. I recently put in 91 and now get 23-24 MPG. (at 6,000 ft. even ) I figured $.02 more per mile. Probably better for the engine anyway.
2003 Mazda Protege 5
Have owned the car since new. Used 89 for a long time thinking it was better for the car. Eventually I learned this was a waste, and used 87 for a long time afterward. However, starting around the summer of 2008 when prices soared to $4/gallon, the vehicle developed knocking/pinging under acceleration. I switched to 89 and even changed companies and noticed an improvement in the rattling and poor acceleration.
Overall, I have noticed that hotter temperatures make the car knock, so I use 89 in the summer and switch over to 87 for the rest of the year.
I have to wonder about the recomendations to “not waste your money on higher octane fuel unless…”
Unless your engine knocks.
Unless your engine going to be under a higher load.
Unless your engine is a high performance engine.
So it seems to have more power. It seems to be less likely to ignite before it is supposed to.
Maybe it doesn’t save you money or increase your milage. Does it make your engine run better?
I am currently trying out the higher octane gas in my 1996 1.3L automatic Geo Metro.
It seems to run better. Since my car’s engine is smaller, I’ve got to wonder, well isn’t it under a heavier load than a larger engine?
Well, we’ll see if it has any effect.