There is next to no load on your engine when travelling at a constant speed down the highway. Hence why you get the best fuel economy doing so.

 

there is only a few ways to boost octane.
toluene is one of those ways.

i'm betting those octane boosters have a tiny bit of toluene in it.
not enough to raise octane tho

 

Level road, no wind cruise load is ~45%, hardly "next to no load"...

 

I will disagree with you, even though I'm a 91 lover.

Your car isn't using all of the power possible at every time to move its weight, for most scenarios it's using under 60-70% of its power (unless you enjoy redlining all the gears at all times...)
You'll use a certain amount of fuel to create a certain amount of power at X rpm.
If the fuel is less efficient (timing retarded), to create the same amount of power the rpm will need to be higher thus you will need to use more fuel. This amount is negligible however on a tank and difficult to visualize. Heck, it's difficult to calculate in real world situations if only for lack of scientific method in MPG calculation... How would you know that on 91 you would have pulled 550 miles but on 87 you pulled 525 miles with so many varying factors on the road?

The biggest tangible loss, which is expressed right the moment it starts burning 87 instead of 91, is loss of power. The rest (more carbon build up, slightly poorer mileage) is apparent over a longer period of time, and chances are you would think it's due to something else since you have no control group to compare against.

There is sense in terms of savings, you just don't save as much as you think you are. You probably will end up saving more money over the course of the life of the car than it would cost you to maintain the car regarding the negative effects of the 87 gas as opposed to 91. As long as you keep the carbon buildup in check, obviously. The biggest trade-off once again is power being produced.

I would enjoy to see a dyno run of 87 vs 91 in a stock TL just for the sake of curiosity.

 

How does retarding spark cause more fuel to be used? Just think about it, did the car magically become heavier? I can see if you say you use a fuel containing ethanol that your fuel economy will take a hit.

 

I believe he meant more fuel to move the same mass at the same speed under all identical conditions.

 

I typed up a few responses to this and each seemed (unintentionally) more sarcastic and condescending than the previous. I'll just be blunt, but please don't take this the wrong way as text is easy to misinterpret sometimes.

While I can't debate you on your point since I have never tried running 87, surely you must realize that outside of these constant speed highway miles, that my previous point applies greatly. Most likely, the effects are most pronounced under acceleration or some kind of variable load. But I'm glad to hear that you don't disagree with the reduced power output, which follows that you don't disagree with the notion that running 87 might be completely nonsensical due to the reduced efficiency of the engine.

Even if a majority of the driving is constant-speed highway miles (which is highly unlikely in any kind of metropolitan areas), the cost benefits of running 87 (because that's the only actual benefit, right?) start to diminish.

Really going to tell the automotive engineers that designed these engines to sod off with their "recommendations" to save a dollar? Let's be realistic.

Edit:

Yes this is exactly what I meant - all things being identical.

 

I'm going to reply to a snippet of your post as now my nerdy curiosity is peaked.

I thought redlining through the gears was the only way to drive it? I mean, that wasn't in the owner's manual so I assumed that's what I have to do.

Just kidding.

But seriously - I totally get your point regarding power output and how it relates to ignition timing. The practical link is how the vehicle speed relates to engine RPM, and thus how the ignition timing relates to vehicle speed. Assuming that the transmission is in gear, the engine RPMs are locked with the vehicle speed. So suppose we want the vehicle to maintain constant speed, this means the RPM will also be constant. Now suppose there is an increased load (up a hill?). At a constant RPM, wouldn't a car running 87 consume more fuel than a car running 91 during this increased load section due to the reduced power output which, as you guys are saying, is a result of the change in ignition timing? Thus it needs to burn more fuel to meet the increased demand for power.

 

Yes the energy in gasoline can vary, but let's say it contains the same amount of energy just different octane ratings, which would require the use of more fuel, closed loop operation, 87 or 91 octane?

 

x2

Good question...

 

Talk about rusty logic.

 

Knowledge is power.

You too can stick finger into an outlet without getting shocked, just do it one at a time.

 

The question here isn't about the energy contained in the gasoline. So for comparison purposes I'd have to say that your assumption of differently octane-rated fuels containing the same amount of energy is a good one for this discussion.

I'm not sure who, but many of the 87 folks in here have already stated that you all agree that there is a reduced power output when running 87. We've already all agreed on that. Okay, let's move to the next thing.

I learned from you guys that the power is reduced because of the spark retardation (of course, we're assuming that there is no pre-ignition occurring). Can we agree on all of these things so far? I hope so, I read them from you guys.

Now, look at my previously described hypothetical situation. Fixed RPMs, fixed vehicle speed, and assume everything is identical in this scenario. Car starts going up a hill. This means that there is now a higher power demand on the engine. Fixed RPM, fixed speed. Since the 87 car makes less power at the same RPM as the 91 car due to the ignition retardation, the 87 car will need to burn more fuel to meet the increased power demand so that the vehicle can maintain speed.

 

How does it not cause more fuel to be used? You cannot create something from nothing.
Fixed mass moving at fixed speed requires a fixed amount of power created at a certain rpm.

Facts we can agree on:
-Retarding timing gives less power
-Higher RPM, higher power generated, let's keep this simple and assume a linear curve
-Mass of car is irrelevant, let's just assume it's always the same
-Speed of car is irrelevant, let's just assume it's always the same
-Let's also assume we are using 1 gear and not 5 or 6, also irrelevant to throw that in the mix

We agree so far? I believe we do.

So if you create less power a given RPM because timing is being retarded using 87 but you want to go the same speed as you would using 91 moving the exact same mass, then you need to... yes, increase RPM!

What happens when RPM increases? Actually, it's the other way around... Why does RPM increase? Because you're burning more fuel.
To put it simply, when you press the gas pedal, you let in more air enter, and the ECU in turn to compensate for this, sends more gas to burn.

This is also why atmospheric pressure/altitude, air temperature, humidity all affect mileage and power, because everything is about the air/fuel mix.

Again, no magic. Can't create something from nothing.

 

No, engine rpm for a given speed is determined by final gear ratio. If cruising at a constant speed (level or uphill) in a fixed gear (e.g. 6th gear), the engine rpm will always be the same regardless of timing. The speed and final gear ratio determine rpm, not timing.

 

Where did I say engine RPM was determined by timing? Arguably, there was a typo, it should have read "at a given RPM".
I think you're being purposely pedantic to avoid holding a proper discussion. Not a bit surprised here.

I said that if you want to create the same amount of power, in the event timing is being retarded because of knock/ping detection, you will need to increase your RPM. This means you will need to press on the gas pedal more to generate the same amount of power.

 

Let me try it again, this time with the typo corrected (but it's irrelevant anyhow). I'm not being pedantic at all. What you are saying about having to increase rpm to maintain the same speed is just not correct. Keep an open mind and listen to what I'm saying here:

If you want to go the same speed, you don't change the rpm. The rpm remains unchanged.

If the assumption is that retarded timing results in less power, then the engine will deliver less power at the crank (or wheels), but the engine rpm will not change while maintaining a constant speed. Does that make sense?

So if relative timing is pulled/retarded, what is the corresponding change the ECU will make with the fuel/air mixture while maintaining a constant speed and engine rpm? The answer to this question will answer the question posed by 6spd-GERCO...

 

I believe you're not reading this the right way at all then.

Let's put fictive numbers, for the sake of it... Once again, fixed gear, fixed environment without any other variables pretty much.

Goals:
-You want to go 50 units of speed

Ways to achieve this goal:
-You need to create 100 power units to maintain this speed
-Your only control is the gas pedal distance, direct correlation to RPM value with a fixed gear. 0% being starting point, 100% being completely pressed down



Case 1:
-At 50% of gas pedal distance you create 100 power units using 91 octane gas.
-Upon observation, timing is not being retarded

Result:
You effectively maintain 50 units of speed



Case 2:
-At 50% of gas pedal distance you create less than 100 power units using 87 octane gas
-Upon observation, timing is being retarded, this explains your lesser power production for the same gas pedal distance

Result:
You cannot maintain 50 units of speed



Case 2b:
-At 50% of gas pedal distance you create less than 100 power units using 87 octane gas
-Upon observation, timing is being retarded, this explains your lesser power production for the same gas pedal distance
-You decide to take action to be able to maintain 50 units of speed in the form of increasing gas pedal distance to 75%
-Upon further observation at 75% gas pedal distance you are producing 100 power units using 87 octane gas

Result:
You effectively maintain 50 units of speed




In Case 2b, did your engine RPM increase? Yes, obviously. So did the air flow and the amount of gas used.

Effectively, to travel at 50 units of speed using 87 octane gas while observing timing retard, you are using more gas.

 

This is getting retarded. In a major way.

 

Vlad - careful pre-ignition and knock are different not the same.

I get what you and polobunny are trying to say. Polobunny I am not saying energy is being lost. What's an engine? An air pump, it sucks, squishes, explodes and blows. Well you suck in air based on the volumetric efficiency of the engine. The ECU in our case uses inputs to calculate the amount of air that has been sucked in and provides the correct amount of fuel for whatever lambda its targeting based on the load and other adders. It's a speed density system.

So now we have a mixture of air and gas in a cylinder, let's ignite it but when should we do that? Well we want to time combustion so that it releases peak pressure at a point where the engine can make the most use out of it or get the best mechanical advantage of the reaction. Fuels with high octanes burn slow and have a more stable burn, this means more ignition lead can be used. More ignition lead results in more torque. Less ignition lead means less torque. It's not that one has more energy then the other it's that one allows the engine to make better use of the energy than the other. The J in the TL's does just that, it's designed for higher octane fuels.

 

I love how you totally ignore me and latch onto a technicality that was a typo.

The answer is that it opens the throttle more because it needs more energy, more air, more fuel.


Haha oops, but I think you know what I meant.

I think you pretty much answered your own question. Less ignition lead means less torque means less power. If the fuels have the same energy content, but one is used more efficiently, then it takes a smaller amount of 91 to do the same amount of work (work defined as a physics term here). So if you could imagine two parallel universes where one of our TLs is driving on 87 and one is driving on 91 under absolutely identical circumstances, the one running 91 will consume less fuel because it converts the energy more efficiently, thus able to travel a greater distance than if it was running 87.

But it sounds like we've pretty much narrowed this down to the following: The TL will operate on 87 octane fuel at reduced efficiency, thus the cost benefit of running 87 octane is diminished (or perhaps eliminated altogether), thus making virtually no sense to go against the engineers' recommendation (see my post regarding engineering terminology in user-facing documentation per industry publication standards) to run 91 octane fuel.

 

This clearly is not the case for highway driving as demonstrated by my readings taken recently (assumes lower temperatures and an elevation of 1600'). As I said before, I've seen zero change in timing or MPG between 87 and 91 under these conditions.

As I said before, I'll be doing more back to back readings under heavy acceleration for further comparison. The roads are too slick right now to do this, so it might be a few days.

WTF are you talking about?

 

It was rhetorical question, I was trying to spark discussion, speaking of sparks are you an Electrical Engineer by chance? I ask because of the IEEE use earlier. I am a Mechaincal Engineer and to save time let's assume I'm never wrong lol jk

Fuel demand is based on load which is constantly changing, so many inputs and variables. It seems to be that premium has a slightly higher Lower heating value than regular more kJ/kg. I saw a decrease in fuel economy when going to 87 for my one and only tank of it, I attribute it to added ethanol.

 

I agree with everything you said but I'd like to add that it depend on a universe. In down-hill universe there will be no difference, in flat-land universe it is quite possible that neither will have advantage, in up-the-hill universe 91 will be more efficient.

Keep in mind that efficiency of internal combustion engine is at most 30%, 70% of fuel energy is wasted.

Now lets say that by using 87 one will lose 15 horse powers 15/260 = about 6% that will translate into less than 2% of efficiency loss (30% X 6%) and that will be only for a brief period of time. (Only during period when 91 is more efficient than 87).

For example in my universe when I fill up with 91 I get 220 miles out of it and when I fill up with 87 I get same 220 miles.

By the way same engineers recommended Z1 we know how that ended.

 

This thread should be more data driven. Rather than go back on forth on various opinions, make measurements.

• We already addressed whether 87 causes engine damage or not, based on input from the manufacturer.
  
• We already addressed engine power, again from the manufacturer.
  
• We addressed to what degree the knock sensor is used and under what circumstances based on experimental data.
  
• We also addressed how much timing retards for given octane levels and load based on experimental data.
  
• Fuel efficiency: Someone needs to drive 10 trips on 93 and 10 trips on 87 and measure the difference in MPG. Drive judiciously in both scenarios, trying to optimize your MPG for both. Record and post your results.
  
  I myself drove more than 10 trips on 93 and about 4 trips on 87. There was no noticeable difference. Seems that other have made similar observations for their driving scenarios.
  
  If you want to argue that it lowers your MPG, do the experiment and show the data.
  
  "Belief," "opinion," even "reasoning" have no merit unless you have data to back it up.
  

 

No one is arguing anything nor do we really have anything to prove. You're the OP that started this entire crusade "DEATH TO 91" for some odd reason and our only assumption is that you really want to save those pennies at the pump. Again, just because you can run it, should you? If you think so, then please continue to do it.

Tell that to the anti-vaxxers. Sometimes data, science experiments, millions of dollars of research and development still don't suffice for some people. I guess the difference between you guys is that IF anything goes wrong (maybe it wont!), you really only have yourselves to blame and you're not inflicting harm on others around you.

 

Sigh....Go back and re-read the thread title.....

 

Thank you very much nfnsquared. My reading comprehension skills are fine. I wasn't aware you were an English teacher.

Riddle me this since you're so keen on posting. Why? Why are you guys so intent on running regular gas?

Because you can? According to my reading comprehension, it's because it provides no knock, no engine loss, no carbon buildup, no issues whatsoever.

If that's the case, GO FOR IT! No one is stopping YOU from doing it.

And in reference to the "title" that you seem to be harping on, my question still lies, "WHY?" Most real scientists do analyses with a purpose in mind. I've yet to establish the purpose for this thread.

Please fill me in because apparently maybe I can't read after all. :rollseyes:

 

I can't disagree with you on this. If the power demand on the engine is such that either fuel can produce the same required power in both circumstances, then of course a difference of efficiency wouldn't be noticed.

My argument revolves around the real-world use case of a car's engine and how the loads are constantly changing, not an ideal scenario. Let's focus on how the engine reacts to an increased load. I thought I gave a pretty good high-level summary of how it reacts to an increased change in load which concluded that more fuel is required. What did you think about that?


Haha yeah, EE.

So glad you said this. Fuel demand based on changing load is exactly my thesis here! When load is increased, the ecu will increase the fuel injector pulse widths to produce enough power to meet the demand (since at that instant, the engine RPM is fixed). Since the lesser ignition advance when using 87 produces a lower power output, then it will require more fuel to create the same amount of energy.

Trust me, I'm an engineer.


Now, normally I am with you 100% - data collected from scientific experiments should drive conclusions.

However, the comparison you've suggested is invalid because the driving conditions would be different for each tank. When setting up scientific experiments, the environments of the different groups have to be identical, one gets the treatment and one doesn't (the control group). A far more sophisticated test would be required than an average MPG of 10 tankfulls.

But, more importantly, these theoretical discussions do have a bit of merit here because we're basically debating the feasibility of saving less than $3.50 per fill up. If we can conclude that more fuel is required to cover the same distance, then this $3.50 figure drops. If we were talking about massive savings, then I'd agree that we should collect more data. But the financial impact of this decision is so insignificant, that I think even a theoretical explanation of reduced benefit should suffice in convincing people to use the fuel that the engine was designed for.

So when we break this down to its absolute essence, the decision is whether or not to use 87 octane fuel to save literally a dollar by going against engineer's recommendations.

Wut. Asinine.

 

Considering the lack of understanding of the basic principles of physics by some participants, I don't think data is even relevant at that point.

Also regarding the data, once again the difference in MPG can be seen when timing is being retarded. If it's being retarded by little you'll have difficulty perceiving any change in MPG over the other factors such as braking/speed/wind/weather and so forth. We're dealing with tiny changes against big ones, which one would you notice? Heck, how would you notice? No control over so many variables = assumptions at most.

This data gives a general idea of the MPG being either not affected or barely affected (for lack of proper precise environment controlled testing) in your driving conditions or nfn driving conditions. Someone with similar driving conditions should expect similar results all things considered.

Pseudo-science non-reproducible scenarios data also has no merit.

 

Let's clarify what we mean by efficiency. We aren't talking about the efficiency of the engine to convert the energy of the fuel into mechanical work. This is only based on how much energy is lost as heat and is irrelevant in this discussion.

We're talking about the required volume of fuel for a given load circumstance. Maximum power is also irrelevant - the engine operates at maximum power almost 0% of the time. it's the instantaneous demand of the engine which will drive a higher volume of fuel into it. This is the most important point. It takes a larger volume of fuel to do the same amount of work as if you were using 91.

The argument I'm making is this. The whole point of you guys running 87 is to save money. What I'm saying is that you also have to take into account that you need a higher volume of fuel when running 87 than 91 which translates into additional cost. We don't know this cost, but it isn't zero.

When you run 87, you save very few dollars. The dollars you save must be used to purchase the fuel you wouldn't need if you were running 91. Thus in conclusion, the cost savings (which might actually not be savings at all, depending on driving circumstances) of running 87 does not justify ignoring the engineer's recommendation to run 91 in the engine that they designed to use 91 for.

 

I agree Vlad...can't believe this thread is still going...

There's always going to be that guy that says "I see zero decrease in mileage and zero decrease in timing for constant speed highway driving."

Having read other posts by said guy I have concluded that said guy is absolutely clueless, even though there's a mid, you have yo be able to do simple math to calculate MPG and I'm sure this guy is not capable.

 

Lol I knew you where an EE.

Lets say we had a drag race (your TLS would beat my TL in the real world ) we had identical cars you ran 87, I ran 91. We floor it from a roll in third gear, high load. The 91 pulls ahead ever so slightly. Engines are consuming the same amount of air and the ECU's commanding the same amount of fuel to react and achieve the target A/F, but our ignition curves are different. We are demanding the same amount of work but getting different outputs from our engine. Work for a given amount of time. In order for the 87 to maintain the same climb rate in your case yes it would need to further increase it's output, more air,more fuel to achieve the same rate of climb as the car with 91.

Was the lack of understanding principles of physics directed at me? I hope not.

 

Absolutely not. At nfn, who seems to believe timing retard doesn't reduce power and that power is created from nothing.

 

nfn's point was that as long as you stay within certain ranges of engine load (<50%, as in highway driving), nothing changes in terms of engine operating parameters.

Again, the chart (data, not my opinion):




Above 50% engine load you start to lose power as you decrease the octane levels. How much this affects your MPG may depend on how you drive. If you're going uphill and you're just trying to maintain speed and not accelerate, probably the affect is negligible. If you're going uphill a lot and trying to often accelerate, it may effect you more.

Meanwhile, if you are saving $0.60 per gallon (on a gallon that otherwise would be $3.00 for premium), you are saving 20% on your gas bill. No way in any reasonable commuting situation is running 87 going to degrade your MPG by 20%.


In order to keep this thread easy to parse, I'm going to summarize up-to-date conclusions at the end of every one of my posts, based on data other people post:

• Use of 87 octane fuel does not lead to engine damage. (based on input from the manufacturer)
• Use of 87 octane fuel does not change engine characteristics below 50% load (based on measured data).
• Above 50% load, there is a loss of power using 87 octane compared to 91 or 93 octane (based on data and manufacturer).
• The knock sensor is used to retard timing across all octane levels, depending on load and octane. (based on experimental data).
• 87 octane fuel costs 20% less than 93 in some areas of the nation. Current measurements of changes in MPG are negligible, if they occur at all. (partial data, still being collected)

 

Right, and as nfn said, the engine at just cruising speeds at a constant speed is apparently at a 45% load (no clue how he determined this... Probably made up in his mind). So that being said, unless you're cruising at a set speed, you're likely going to cross that 50% load threshold.

Although wind resistance does play a role in all of this, based on speed, and according to nfn he's at a 45% engine load at highway speeds, I can't imagine that cruising at city speeds will reduce load super drastically.

I'd also like to add that whoever posted that chart originally did say they were interpreting results, so that chart may hold zero validity, beyond being a pretty picture. But I digress...

 

nfn has an ECU scanner. Stop the attacks. This thread is not for ego or emotion. This purpose of this thread is to post data. If you do not have data to post, do not post.

CURRENT THREAD CONCLUSIONS SUMMARY:

• Use of 87 octane fuel does not lead to engine damage. (based on input from the manufacturer)
• Use of 87 octane fuel does not change engine characteristics below 50% load (based on measured data).
• Above 50% load, there is a loss of power using 87 octane compared to 91 or 93 octane (based on data and manufacturer).
• The knock sensor is used to retard timing across all octane levels, depending on load and octane. (based on experimental data).
• 87 octane fuel costs 20% less than 93 in some areas of the nation. Current measurements of changes in MPG are negligible, if they occur at all. (partial data, still being collected)

 

*sigh*

For those reading this who are on the fence about running regular, please don't.

For those that already do, please disclose this fact if/when selling the car. If you stand by this so much, then post your VIN numbers here so that there is a database of cars which run 87 octane so that buyers know what they're buying.

Last observation: I'd love to contribute data, but I'm not willing to put 87 in my tank so you won't see anything more from me.

Fuck this, I'm out.

 

I never touted that there would be a difference in MPG if there is no additional timing retard. I said "no timing retard" regarding 91 to make it simple for understanding, not for ignoring the facts there is already modifications being applied. This is somewhat outside the scope of the understanding of the basic concepts that apply and would only further complicate the explanation.


The problem with the data collected so far is that it applies to very specific situations and not to all of the situations you will encounter in life.
It does not apply to people living in warmer places, it does not apply to areas that are not flat, it does not apply to city driving. It's data collected mainly on the highway while trying to keep a steady speed, where by all means is where the fuel performance matters the less.

Regarding damage due to using 87 octane gas and Acura agreeing there would be none... I have no idea how you gained that information other than by twisting the meaning of words and contacting a level 1 clerk with bare minimum knowledge of the Acura powertrain.
I'm not trying to remove anything from people analyzing the words "Recommended" and "Required", but this basic semantics. It is not a fact but an interpretation.


Actual current thread conclusion would be more in the vein of:
-Use of 87 octane fuel does not seem to lead to engine damage. (based on anecdotal evidence)
-Use of 87 octane fuel does not change engine characteristics below 50% load in tested situations (based on measured data).
-Above 50% load, there is a loss of power using 87 octane compared to 91 or 93 octane in tested situations (based on data).
-The knock sensor is used to retard timing across all octane levels, depending on load and octane. (based on experimental data).
-87 octane fuel costs 20% less than 93 in some areas of the nation. Current measurements of changes in MPG are negligible, if they occur at all. (partial data, still being collected)


Applying limited data sampling to everyone and every situation is just a recipe to disaster. I'll go with Vlad in saying that those on the fence of running regular, please don't. The data provided so far by the limited situations tested is too minuscule to draw a proper conclusion to know whether or not your car will be damaged or if you will save as much money as advertised.

 

HEY! May I pump diesel fuel into my car instead of standard ol' 87...?!??