Using a lower octane fuel than recommended

[OVERKILL]

Yip how about OBP?

Old Bags o' Poo?

 

[TiGeo]

When I run 20-25% E, I don't see much of a mpg difference...it's a bit lower but not my a lot.

 

[Zee09]

Old Bags o' Poo?

Old rap song...lol

 

[mightymousetech]

Then how is it telling you what gas is in it?

Every time you fill up, the engine determines the octane by advancing the ignition until knock occurs.

Low=87
Medium=89
High=91+

 

[TiGeo]

Every time you fill up, the engine determines the octane by advancing the ignition until knock occurs.

View attachment 82397

Ah nice, interesting way to do this! My VWs do not record it but they do the same - ride the knock sensors and then back off as needed.

 

[mightymousetech]

Ah nice, interesting way to do this! My VWs do not record it but they do the same - ride the knock sensors and then back off as needed.

My 135i has a forth rating for 93+.

 

[MRC01]

What is the thing with zero E gas? Unless you have a really old car, the little bit of E helps with knock and at 10% the mpg diff has to be minimal.

Whether the E helps with knock is debatable. Ethanol has high sensitivity, meaning a big spread between RON and MON. It measures high octane under light load (when you don't need it), but when you increase the load, its effective octane drops (when you need it most). Other octane boosters like Xylene and Toluene are less sensitive, narrower RON/MON spread, more effective at reducing knock.

Combined with its low energy content, and its short shelf life, and its corrosive/dissolving effect on engine internals, ethanol is not a good fuel. Ethanol mandates don't save energy or reduce carbon, they exist only because the Agribusiness corn lobby is powerful.

 

[walterjay]

Lower octane fuel does not burn hotter nor cooler, have more or less energy content, burn faster or slower, burn less or more completely, ignite less or more easily, nor does it make you dinner. A required octane rating in the owner's manual is what the engine design requires as a minimum and if the ECU is able to alter the ignition timing then it may be able to make use of a higher octane gasoline to be more efficient. Where that efficiency increase falls in relation to the higher price for the fuel is hard to determine since AFAIK no one publishes efficiency numbers in their owner's manual.

I was under the impression that higher octane fuel burned a little cooler. I remember an article about a guy with an air cooled VW. He has temp sensors on the head. He stated that in summer hot weather he went to higher octane because the temperature on the head would be 10 degrees cooler. Also I had a Kawaski 25 hp lawn tractor that ran hot and would run on after shutdown. Using premium gas pretty much solved the problem. How does all this come into play?

 

[123GO]

In a nut shell as long as it don't ping your perfectly fine.
Most newer engines will not ping today unless you get bad gas or they have an issue like bad sensor or carbon build up because the computer compensates everything today. Wife has owned a 2000 Infiniti since new with 10:1 compression so we ran the 91 octane thats "Recommended" for years until I learned as long as we only get gas from Top Tier gas stations (see link for info/list) then it makes no difference on the grade anymore and we've ran the lowest for many yrs now. Our MPG remains the same regardless too.

But' If we buy low grade from Non Top Tier fuel stations like many convenient stores sell not only will it ping it will throw a light right off the bat too, I guess thats "Pong"?..lol
One day I filled it up at a convenience store and only drove a mile or so away and it threw a light that fast. Thats when I first learned about Top Tier gas and whats been going on for years between our gov, gas corps and car makers. Learning all about Top Tier fuel was an eye opener for me.

The fact is the key words are "Recommended" vs "Required" that are used by your car maker but' the key problem here is "Ping" aka Spark Knock.
If it pings a little bit off/on (NOT CONSTANT PING) no damage occurs. In fact old drag racers will tell you that intermittent ping tells them timing was set perfectly, its maxed.
Turn distributor till the engine pings/drag starts then back it up a ticks turd, your sweet spots right there. We always ran them like that because you couldn't use a timing light on our race cams so thats what we all did on street or strip, muscle cars. Just a note there:

But' todays computer cars adjust timing/air/fuel etc for you so today pinging can mean bad gas, a sensors going bad or carbon buildup so if pinging is constant or engine still pings after two tanks of Top Tier High Octane fuel keep that in mind. Failing sensors are known for causing it with/without throwing a light.

Again, Higher Octane fuel is either "Recommended" or "Required" with higher compression engines and worrying about pinging started from older cars without sensors/computers that didn't compensate to stop ping like all newer cars do now.
My 1969 Super Bee I drove as my daily till 2012 with 425+hp & 13:1 compression with full race cam would ping intermittently on 87 grade but never ping on mid 89 grade using Sunoco/Shell gas only. I never ran the highest grade with their fuels, but I always had to run 91+with other stations including Marathon. People saying it makes no difference where you buy your gas at are dead wrong, its not all the same fuel mix unless some really shady chits happening in your area. Some cars actually tell you who has the bad fuel around town if you only listen closely, but octane levels rarely matter on new engines now days, super cars, race engines mainly do Require it. Most only Recommended it!
See links-

Good write up on octane fuels here..
https://www.hemmings.com/stories/20...-the-fiction-behind-those-higher-priced-fuels

All about better Top Tier fuels here...
https://www.toptiergas.com/why_top_tier/

 

[JustN89]

6th gen Maxima- fuel door recommends 89+, yet over 128k miles it's never seen a drop of anything above 87. No issues with fuel economy, power, or pinging.

 

[TiGeo]

Whether the E helps with knock is debatable. Ethanol has high sensitivity, meaning a big spread between RON and MON. It measures high octane under light load (when you don't need it), but when you increase the load, its effective octane drops (when you need it most). Other octane boosters like Xylene and Toluene are less sensitive, narrower RON/MON spread, more effective at reducing knock.

Combined with its low energy content, and its short shelf life, and its corrosive/dissolving effect on engine internals, ethanol is not a good fuel. Ethanol mandates don't save energy or reduce carbon, they exist only because the Agribusiness corn lobby is powerful.

It helps when I run a E20-25% blend and it's undeniable - it's magical stuff in the tuning world.

 

[Finklejag]

The 06 Acura TL I bought a few months back calls for 91 and the previous owner said he always used 87 without a problem. Well I been using 87 and been getting 27mpg on a 160,000 mile engine.

 

[MRC01]

Back when 92 octane disappeared in California due to changes in the state gas formulation requirements, replaced by an ethanol based 91, my SCCA race car (a Panoz Roadster powered by a Ford Cobra 4.6L V-8) dropped 10 RWHP due to the fuel. I had before/after dyno runs temperature/pressure/humidity corrected for comparison. On the dyno when you hit the throttle you'd hear a ping or small pre-detonation "crack" then the torque/power would suddenly drop as the knock detector triggered and pulled timing. I bought a big jug of Xylene or Toluene at the hardware store and mixed it 1:10 with 91 octane pump gas which bumped it to 93 octane, went back to the dyno and retested - full power. So I did this for all the SCCA events. This worked great for a while but soon after, large sizes of Xylene or Toluene disappeared from hardware stores, likely a result of drug prohibition. It seemed that one way or another, the CA legislature was bound & determined that cars like mine would not have the gasoline they were intended to have, and consequently not produce their rated power.

Modern cars may be designed to burn higher %s of ethanol, if so they may be less impacted.

PS: that Ford Cobra V8 wasn't the only engine affected by the crappy new 91 octane ethanol gas in CA. It also caused my wife's GS430 to ping at anything more than 1/2 throttle. You could actually hear the light rattling sound of the pinging as you pushed the throttle. So that engine was also pulling timing and down on power, though I didn't dyno test it since we weren't racing it.

 

[TiGeo]

Back when 92 octane disappeared in California due to changes in the state gas formulation requirements, replaced by an ethanol based 91, my SCCA race car (a Panoz Roadster powered by a Ford Cobra 4.6L V-8) dropped 10 RWHP due to the fuel. I had before/after dyno runs temperature/pressure/humidity corrected for comparison. On the dyno when you hit the throttle you'd hear a ping or small pre-detonation "crack" then the torque/power would suddenly drop as the knock detector triggered and pulled timing. I bought a big jug of Xylene or Toluene at the hardware store and mixed it 1:10 with 91 octane pump gas which bumped it to 93 octane, went back to the dyno and retested - full power. So I did this for all the SCCA events. This worked great for a while but soon after, large sizes of Xylene or Toluene disappeared from hardware stores, likely a result of drug prohibition. It seemed that one way or another, the CA legislature was bound & determined that cars like mine would not have the gasoline they were intended to have, and consequently not produce their rated power.

Modern cars may be designed to burn higher %s of ethanol, if so they may be less impacted.

PS: that Ford Cobra V8 wasn't the only engine affected by the crappy new 91 octane ethanol gas in CA. It also caused my wife's GS430 to ping at anything more than 1/2 throttle. You could actually hear the light rattling sound of the pinging as you pushed the throttle. So that engine was also pulling timing and down on power, though I didn't dyno test it since we weren't racing it.

A modern turbo car will eat up the corn especially when tuned - most large hp tuned 4 cyl turbos that tuned to run E85 in some varying %. The old-school V8...I can see that not doing much b/c you need to increase the amount of fuel to make up for the less energy dense ethanol, a modern ECU handles that (until you run out of fuel pump capacity).