Octane experiments

AZjeff

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I've always just put regular gas in my vehicles, never saw the need, never had one that called for higher grade. Some recent threads and my BIL talking about his results using premium while towing got me a little curious so decided now gas price has come back down I'd try different grades. The '02 Xterra is our DD so it made sense to use it and it's pretty gutless so maybe any difference would be noticeable. Premium where I get gas is 91 so I started with it. I can't say I noticed any difference in power, smoothness, starting, and the mpg for the tank was right in line with normal fill ups. I hand calculate every tank by habit. There was one thing that happened that indicated a difference. On a 4 lane bypass road that I drive 2-3 times a week every week and have hundreds of trips on it by now there's a 1 mile uphill grade, not steep, that every time @ 65 mph the Xterra will downshift around 3/4 of the way up. Every time. With the 91 gas it has not downshifted one time. I ran 2 tanks of 91 and it pulled the grade every time. I use cruise at 65 and it hasn't mattered time of day, temperature, wind direction. I then ran it low and filled up with 89 and saw the same results, nothing notable while driving but it pulled the grade over the top every time through 2 tanks and I'm into the 3rd tank now. Fuel mileage right in the range I'd see with 87.

My guess is the higher octane is holding timing and it's just enough to pull the grade. This to me is more than anecdotal, in 4 years of traveling this road in every condition the Xterra has always downshifted, now with both 89 & 91 it has not downshifted one time. Is this little thing enough to make me want to run 89 at 25 cents more per gallon? Likely not. On our next towing trip I'm going to run some tanks of 89 out of curiousity.
 
only 25cents? here it is 30-40cents more and premium (92 or 93) is 60-$1.10

Premium was great in the jeep during summer heat towing.. of course it made 135hp/liter

The subaru will likely never get anything except 87.... of course its power density is almost half that of the jeep.
 
GM and a few other makers have stated they want a new high octane standard. They can build engines that get higher fuel economy along with lower emissions. The problem is that most are addicted to the cheapest gas at the pump. GM doesn't want Joe Dumb buying a new GMC Sierra that needs high octane and filling it with 87. We are not getting the more fuel efficient gas engines we could. They are working with the petro industry on ways Joe Dumb doesn't put 87 octane in his truck, but the auto makers really just want 87 to go away like leaded gas did.
And before my time, some people bought 1975 cars that had a catalytic convertor and used a funnel so they could buy the cheaper leaded gas.
 
... Some recent threads and my BIL talking about his results using premium while towing got me a little curious so decided now gas price has come back down I'd try different grades. ... There was one thing that happened that indicated a difference. On a 4 lane bypass road that I drive 2-3 times a week every week and have hundreds of trips on it by now there's a 1 mile uphill grade, not steep, that every time @ 65 mph the Xterra will downshift around 3/4 of the way up. Every time. With the 91 gas it has not downshifted one time. ...
I wonder if a gasoline of the same octane, but with higher energy density, would have the same effect. Can you find non-ethanol gasoline in your area?

Remember that ethanol based 91 octane is not truly 91 octane when your engine needs it most. Octane is (R+M)/2, and ethanol has high RON but low MON, which means its octane drops under heavy load. Another way to say this is that sensitivity refers to the difference between RON and MON, and ethanol has high sensitivity. Other octane boosters like Toluene or Xylene are less sensitive. Because of this, some cars made to run on 91 octane gas may ping or pull timing on ethanol based 91 octane.
 
I experimented with using 89 in my Kia Soul GDI during the summer and noticed less pinging, and it may have been in my head but it felt a little more responsive. It’s only a little 1.6L 130hp engine so every little bit helps. In the winter now that prices are only about 25¢ different between 87-89, I am continuing to use it. Can’t hurt any.
 
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@skyactiv, interesting and totally outside the intended scope of the thread. So the owners of the 100 million cars on the road now will be forced to use higher octane and one would expect more expensive gas with no benefit? Not sure a guy is Joe Dumb not wanting to spend more for gas unless it's offset with the higher efficiency.

I was just wondering and maybe hoping I'd get some of these noticeable performance improvements that some say happen and some say are impossible but unfortunately I can only point to one very specific example. I really wanted the butt dyno to register positive impressions.

Is it correct to say octane provides more power or rather that it doesn't lose power that the engine already has when it detects ping and pulls timing?
 
Is it correct to say octane provides more power or rather that it doesn't lose power that the engine already has when it detects ping and pulls timing?
Sort of neither one in and of itself since the overall energy density is the same. It allows a higher compression ratio and/or advanced timing which increases efficiency. You can extract more of the available energy. In your instance since you cannot increase the compression ratio, unless you can advance the timing then increased octane rating won't do a thing. Some engines can (or will) but some will not. Your test isn't conclusive due to the many variables present but monitoring the advance would show if the fuel is making a difference.

This is why automakers want higher octane fuels as minimums. It is a legitimate way to increase efficiency.
 
@skyactiv, interesting and totally outside the intended scope of the thread. So the owners of the 100 million cars on the road now will be forced to use higher octane and one would expect more expensive gas with no benefit? Not sure a guy is Joe Dumb not wanting to spend more for gas unless it's offset with the higher efficiency.

I was just wondering and maybe hoping I'd get some of these noticeable performance improvements that some say happen and some say are impossible but unfortunately I can only point to one very specific example. I really wanted the butt dyno to register positive impressions.

Is it correct to say octane provides more power or rather that it doesn't lose power that the engine already has when it detects ping and pulls timing?
Higher octane only benefits you if you can reduce timing correction/get more timing advance. Period. The only way to tell this is with either 1) data logging and/or 2) performance logging i.e. 1/4 trap speed data etc.

Here is just that - my '18 Atlas on 87 vs. 93, conditions were nearly indentical. Single second to third gear pull, same road, etc. Less timing correction/knock on 93. I still run 87 b/c at nearly $1 more a gallon here (unless you hit Costco where it's about $0.30 more), there is no value in that vehicle/it's daily use. Butt dynos are worthless for this v. small difference at WOT. Car-based MPG data are also worthless due to the immense amount of variables that can impact mpgs and the fact that you would need massive data before/after the switch to average them and be meaningful.

Atlas 87 vs 93.jpg
 
Your test isn't conclusive due to the many variables present but monitoring the advance would show if the fuel is making a difference.

I think this test is conclusive that the higher octane fuel is doing something I just don't know exactly what. When the car always downshifts under all conditions over the course of years and and possibly hundreds of trips and now never downshifts over 4 tanks of higher octane gas under all conditions encountered so far wouldn't you say the octane is the reason? Always downshift vs never downshift. This isn't a subjective observation.

I don't know much about ECU programming. Knock sensors cause the ECU to pull timing out which reduces power. Does the ECU in an '02 Nissan advance timing right to the point of knock or is there a set point? With higher octane would it advance timing further and make more power?

Does higher octane allow this engine to make more power or does it prevent the power it has from being reduced? 2 different things.
 
Gasoline with a higher octane rating may allow an engine to extract more of the available energy from the fuel. Assuming the engine can do so.

The rest of your post about being able to determine that via butt dyno is a big nope. TiGeo nailed it above.
 
I've noticed better response with premium, when towing, and definitely during the summer with a few vehicles.
I don't believe in 'anecdotal'. I believe in the antidote called experience. And, I can tell a difference with my butt dyno. I guess if someone is so mentally incapable of noticing anything, like most of society, then no one wants to believe in 'experiences'. I am not a drone zombie driver, like 98% of the consumers out there.

Its for you to decide whether the cost/benefit is worthy to you. In the SUV, my 2gr gets 87 almost year round and 91-93 only when towing/hauling, and is noticeable. The same engine in the sedan runs fine no matter what octane since its 1000lbs lighter and grossly unstressed. My 1.4T gets premium ALWAYS since its a dog without it. Intercooler is borderline ineffective and will be modded soon. It was a rocket with the cold weather the past few days.
The theta2's get regular during the winter. During the summer, premium is a must if you don't want to have to put the pedal down to the floor to get moving. My 3.0 Camry was similar and begged for premium. My same body 2.4 Camry not so much.

I've muted enough knock sensors in the last 25 years to know which of my engines depend on the sensor. Almost all detonate drastically more with 87 vs 93. I didn't need the scan tool. My ears verified what I already knew. Youre no need for downshift verified what you already know. Accept it.

Another thing to try, is to improve engine cooling, intake air cooling, and engine cleaning.
Remove some piston/cc carbon with a quality PEA/equivalent fuel cleaner and see if you still require the hill climbing downshift. Fuel cleaner will also clean the injectors and provide possibly better fuel atomization.
If GDI, run an IVD cleaner.
If the thermostat is 10+ years old, replace it and the radiator cap. Use a good quality 50:50 coolant or maybe a little more water if weather allows. One can also bypass the TB coolant heater loop if weather allows. Take your yard hose and blast the lifetime of dirt/bugs debris out of the radiator.... I use the car wash pressure washer to keep the radiator, ATF, oil coolers, condenser... clean.
When the radiator failures, check to see if the vehicle has a heavy/duty or tow radiator, oversized, or all aluminum, and upgrade when possible.
When my radiator fan failed, I upgraded to the higher output fan since I had the HD radiator already.

Reduce drag with proper tire PSI. Use a quality synth ATF, PSF, front/rear diff gear oils, transfer case..... and get a good alignment. Destress the daily commute load. Live on slimfast.
 
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only 25cents? here it is 30-40cents more and premium (92 or 93) is 60-$1.10

Premium was great in the jeep during summer heat towing.. of course it made 135hp/liter

The subaru will likely never get anything except 87.... of course its power density is almost half that of the jeep.
Premium here isn't much more than regular
 

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Premiim gas does make a difference in most cars. Since 1996 OBD1 the ecu has 2 maps, one for regular and one for premium. It was slow to adjust and people did not notice a difference. As ecus became more advanced and compression ratio increased bigger gains were noticable. The biggest hurtle is Ve because that percentage has to overcome before gain.

Now with variable cam timing and better ecu it will detune to the octane being used. VE is higher and the better mpg I see is from lower loads at lower rpms from higher usable compression. 87 to 93 rm is about 6 percent increase. Octane requirements changes too and a 10.5 to 1 compression octane requires 110 Ron fuel to out of knock limited. Yes you can run lower octane even lower than 87 but you will lose power and mpg and driveability.

DI motor are not knock limited so but torque limited. Premium in my Pilot makes a big difference but is it needed no but I use it when towing and hwy trips otherwise I just use regular. My Civic is turbo so huge gains is seen. Because the 10 horsepower the motor gain from premium alone is multipled by the boost.

Get a gauge that shows fuel trims and timing. You will see a difference. Been monitoring mine for 10 years.
 
@Greasymechtech, thanks for the car maintenance lesson, mostly got it covered. Wasn't really looking to maximize performance of a 2002 DD Xterra but appreciate it.

This was just a little experiment to see if I could feel anything different but happened to have 1 verifiable/repeatable result. Learned a lot about how this all works. No need to buy scan tools and all that stuff.

Maybe this isn't the vehicle and I'm not the right driver for that, I don't go WOT from lights or hit on ramps at 10/10s and note speed at the merge sign etc. Not to say I'm not sensitive to how it runs, vibrations, sloppy mechanicals.
 
You did maximize it... with a tad more octane, as long as that octane isn't covering up something else. Since you have maintenance covered, enjoy the midgrade. If it starts downshifting excessively on grades when the weather warms, might need premium.
 
I remember reading a post on a mower forum where a guy said he always runs Premium in his ZTR with a two cylinder Kohler engine . He claimed that his mower would " Start quicker , make more power , and run cooler " ... These kinds of threads remind me of that nonsense .
 
I remember a world with people that did things themselves and had even 'senses' available that they'd notice something. Now, most just rely on headmeds and go thru life glued to their phones like zombies and drones, and wouldn't notice a barn wall until they crashed into it, and then only maybe notice the hole in the barn behind them.

Sorry world we live in. The days of using senses are gone. I can hear and identify engines starting or running across a large parking lot, and hear issues with many of those engines from a distance. I can feel the difference among identical engines simply by putting my hands on them. But most fools wouldn't even notice a spark plug missing without a scan tool. I guess those of us that worked with carbs/distributors are a dying bunch, as is anyone that got their hands dirty in an industrial setting.

Stick with your tuning shops, dealers, forum hype, and indie mechanics. Most are too useless to even make comments.
 
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