octane/HP rumors?
 

ok i must have came across 10 different websites by now stating that what people beleave about higher octane giving you more power is actually flase. is that true? cuz i know when i run 93 octane as oposed to 87, it seems to have more power and i definatelly get more MPG. so how can that be?

There's no rumor, it's a fact. I'm glad I saved this when I typed it the first time:

Here you go:


Unfortunately, many people assume that higher octane fuel is better for all engines, no matter what. This, as I'm sure you know, is absolutely false. Ultimately, the best octane for any vehicle is the lowest one you can run without detonation (pinging) occuring.

Running too high of an octane will ultimately make it necessary to continue using that octane.

Just to clarify, it's not the fuel that increases the performance, it's the fact that the timing has been advanced. The higher octane permits this to happen. Basically, the way it works is something like this:

Octane represents a fuel's stability. When you compress an air fuel mixture, it becomes quite unstable, and explosive. In fact, this is why diesel engines don't require spark plugs. They commonly have compression ratios of 22:1 (as opposed to a stock Mustang with 9:1), which makes the air/fuel mixture so explosively unstable that it ignites itself when the piston reaches TDC.

Octane, for all intents and purposes, is used to slow down, or control the burn rate. Modifications that increase performance, such as increased compression, or advanced ignition timing, will cause the mixture to become too unstable, and pre-ignition (aka: detonation, pinging) will occur. This is when the mixture fires on it's own, at the wrong time. Severe damage will occur if left untreated. Anyway, the only way to perform the mods that increase the power is to further slow down and control the burn rate of the air/fuel mixture, and the method used to do this is increased octane.

People often think of high octane fuel as being more flammable, and easier to explode, whereas that is actually the opposite of the truth. 110 octane race gas is much tougher to light than low grade 87 octane. BUT, because of that fact, it is the use of 110 octane fuel that permits the compression to be increased to 12:1 without melting the pistons.

On a side note, nitrous oxide works on a very similar principal. With nitrous, the power comes from the added oxygen. The problem has always been trying to find a way to add oxygen safely. As I'm sure you know, oxygen is EXTREMELY flammable, and if you were to try and add it straight to your engine, you would likely die, and not even be able to explain to people why it was you died. It was discovered that the nitrogen in the nitrous oxide was just enough to keep the oxygen from burning uncontrollably, thus permitting it to be used in a gasoline engine. In other words, the nitrogen is to nitrous oxide what the octane is to gasoline, except for the fact that octane is a calculation, and nitrogen is an actual element, but you get the idea.

Okay, back to the story...

Use of a fuel that has a higher octane than is required by the engine and the way it has been tuned will result in unburned deposits being created and left behind in the combustion chamber, and on top of the piston. Often referred to as carbon deposits, these cause the combustion chamber to become very unstable, for several reasons, all of which will ultimately require you to use a higher octane fuel to restore stability. Among the reasons, are increased compression (the deposits take up space, and actually increase the compression enough to make it unstable), retained heat (deposits retain heat at times when those surfaces shouldn't, increasing the likelyhood of pre-ignition), and the development of sharp edges (like sand under the waves, carbon deposits can be "shaped" by their environment, and can develop sharp edges, which act to the compressing mixture like a hat pin would to a balloon.


Take care,
~Chris

I just realized that you're the same person that I already answered this to today.

look guy, I do have better things to do than to answer you again and again just because you didn't like the answer. You don't have to believe me, but if you ask a question, accept the answers you get and move on, don't keep posting it. You waste server space and my time.

i didn't ask this specific questions earlier, i asked another question, your answer just remained the same. because it answered both questions, i just wanted other peoples opinions on THIS exact question too.

also with the facts... that higher octane does not incress power, only reduces detonation. well that would be half true... because my car (with 9.5:1 compression) DOES have more power with 93 as oposed to 87. this is because (im my best guess) with 93 reducing detonation, my timing stays advanced as where with 87 my timing gets retarded alittle. there for in any vehicle where the timing is being retard by even the smalled amont of detonation, higher octane fuel will incress power. up to the point where all detonation is eliminated. if all detonation is eliminated with 93 octane, then 100 octane isn't going to up any performance.

But again it's not the higher octane that is increasing power, it is the timing. The octane just allows the timing advance.

thats true. but in the same sense, without the higher octane the timing can't be advanced. yes the timing is actually uping the power, but the octane is allowing it to do so. the octane itself cannot make power, yet the timing cannot (safely) make more power without the octane. so techniclly the octane does not boast power. but in reality, it does boast power by allowing the timing to stay advanced.

Octane does not create power, period. It simply allows power making changes to take place. If you took an engine, and placed it on a dyno w/ 87 octane fuel, and rung it as hard as it would go, and it didn't have any mechanical failures, and then ran the same engine, the same way, but with 93 octane fuel, the results would be the same, OR LOWER with the 93 octane.

You have a better chance of slowing down with higher octane than you do of going faster. Understand this: higher octane essentially means less flammable, slower burning fuel.

Do not believe for a minute that simply using a higher octane fuel will make a stock n/a vehicle faster, because it ,won't.

I would like to see time slips from your experience.

Take care,
~Chris

You are starting to use circular logic to get the answer you are looking for. Note, not actual figures for any car I konw of.

Consider this:

At tdc, 87 and 93 octane make 200bhp.

At 5 degrees btdc both make 210bhp.

At 10 degrees btdc both make 215bhp.

At 15 degrees btdc, 87 predetonates and 93 makes 220bhp.

One could say look, I get more bhp (220 v 215) running 93. However you only get such by running in an area not accessable by 87 octane.

Now go with stock intake v. CAI.

At tdc stock 200bhp, CAI 210bhp

At 5 degrees btdc: stock 210bhp, CAI 220bhp.

To determine the actual power benefit of a variable, you can only change one at a time. It's obvious in the example above that a CAI gives you more power than stock, period. It also shows that 93 will give you more flexibility in setting the timing, and thus allowing more power in certain applications. But in and of itself, higher octane does not boost power. It only allows you to do other things that actually make more power. So if the car runs fine on 87, any 'increase' from 93 will be purely placebo effect. You should theoretically notice a decrease in power, all other things being held equal.

Set your timing, and then run the lowest octane gas possible. It will save you money and headaches.

i completely understand that octane itself does not incress power. im simply saying in most cars (with knock sensors) it can incress power by eliminating any detonation the knock sensor is picking up there by stopping the timing for being retaded. even just unpluging the knock sensor can inprove performance, because knock sensors offen pickup sounds thats not neven detonation.

And you would simply be misstating the fact. It is because the knock sensor does not retrard timing that the power is there. There are other ways to 'fool' the sensor, like unplugging it. So then does unplugging the knock sensor increase power?

To get a solid yes answer to your question it would have to be shown in a controlled environment. So unplug the sensor and run both types of gas. You won't see any difference, unless the knock sensor was actually doing its job with the 87. I don't recommend it, but I hope you get the point.

yes, unpluging the knock sensor does incress power(at least with my engine it did), its only a very small amount we're talkin' about here, not 50 HP or anything... and it does so because knock sensors almost always retard the timing, even when there is no detonation. because they're so sensitive.

He also asked about MPG's. When the knock sensor detects knocking wont the computer also add fuel if it needs to? If so adding a higher octane would stop pinging stop the addition of extra fuel and "Increase MPG's" is this correct or does it only take away timing?

The knock sensor justs tells the ECM to reduce thue amount of advance that it has implemented.

Gizmo, you areone stubborn little schit. That's pretty cool, usually, but you're getting to me.

High Octane does not increase power by itself, PERIOD.

You can draw circles and squares, and twist this and bend that, and even add a bottle of compressed air, but it won't change that fact.

let me try putting it another way.

Some fancy restaurants have a tie policy. All men must wear a tie, or they aren't permitted to dine there. Many are by invitation only.

Now, does that mean that the tie itself got you dinner in a fancy place? No. It just made it possible for you, if you decided to, to get past the front reception, provided you met every other standard they had.

You need a different hobby. Lego maybe.

;)

Take care,
~Chris

Octane myths and facts
 

gizmo83:

As PKRWUD stated, simply adding 93 octane gas to your tank will not increase HP or performance over using 87 or 89 octane gas. Advancing your timing will give you some more power and the higher octane allows you to do that, as you stated. I think that's obvious.

I've run 15 degrees of initial advance on my near-stock 5.0 since I bought it, new, in 1990. I've also run Sunoco Ultra 94 octane in the tank for all 118,000 miles on the engine.

My injectors are clean, my valves are intact, my 5.0 runs strong and sweet and I've never regretted the extra cost of the gas.

As a side note: I run 12 degrees advance on my wife's '95 Mazda 626 2.0 (stock is 10) with 87 octane gas and never a problem in seven years.

If you want to run 93 octane gas (and advance the timing) do so and enjoy the benefits but don't run the 93 octane with stock timing and expect better performance...it won't happen. The seat-of-the-pants dyno is highy inaccurate.

PKRWUD, like i've said in my last few posts... i completely understand octane does not incress power on its own... on its own it does nothing but reduce the likelyhood of detonation... but it does allows timing to stay advanced, there for with the "help" of octane, the timing incresses the power which is could not do without the help of octane. yes octane by itself does not increse power. period.

for some reason we are all talking about the same thing and getting nowhere. so whats the problem?

as for higher octane being better for engines, that is partially true from what i have read. let me explain. the higher octane 93 has more detergents in them than the 87 does (this is advertised and i cannot truthfully prove it). so it will clean the injectors a little bit as stated by the companies themselves. like i said, "they" say the put more detergents in the higher octane to make your car run "cleaner". as for it being BS, i wouldnt know. just thought i would mention that.

HAHAHAHA!:D

i sort of understand what hes trying to ask but here another one for you standard helicoter fuel jp 40 is 40 octane. its a kerosene chemical mix

I wouldnt get in if you filed it with 93 to give it more power.

when my dad was young they would put avgas in there cars to run faster avgas about 60 octane. no computers or knock sensors in his flat head

I understand what he is trying to say as well.

He wants to hear a yes to a question that the answer is no. All things being held equal, there IS NO gain from 93. Period.

If I do nothing but hook up a 150 dry shot, I'm going to see extra power until I blow the motor. Same with a blower. Not the same with 93. It just doesn't happen like that.

i do not want a yes when the answer is no.. i give up. if you'd read the posts you'd know that i understand higher octane HELPS to up power (by allowing timing adjustments/higher compression/ect). and that i know IT DOES NOT DO ANYTHING BY ITSELF. like srv1 said: we are all talking about the same thing and getting nowhere.

Octane
 

I always use 93 octane in my 91 5.0 because I was under the impression that it is better for my engine because of all the detergents it contains. I've run 89 before with no problem, I just usually opt for the 93. After reading this post particularly what prkwud stated I now think I might actually be doing my engine harm. Is this right? Should I use the 89 octane from now on? I'm not trying to get any horsepower gains from using either one, I just want to use whatever is better for my engine. I do have my timing slightly advanced, but like I said there is no knocking when I use 89.

rppngears:

I see no real harm in using 93 octane (I use 94 and in 12 years I've never had the slightest gas-related problem) but as PKRWUD stated, running the lowest octane you can - without detonation - is probably the best way to go. If you can run advanced timing with 89 octane, go for it. If you can do it with 87, better yet. Experiment. My Mazda 2.0 runs 2-degrees advance with 87 octane, my Mustang won't do that and requires more. Every engine is different.

The gas companies do claim the higher octane gas contains extra 'detergents' to help keep injectors clean. This sounds plausable and my injectors are clean after well over 100,000 miles of using 94 octane but I've also heard this is BS to sell higher octane gas which also sounds plausable.

I basically ignore the 'detergent' factor (but suspect it's true from my own long-term experience) and just crank up the timing and fill up with Sunoco Ultra 94 every week. Works for me.

FWIW, there are only 3 or 4 sources for the gasoline you buy, and they are pretty much the same. Brand loyalty means very little, and the detergent issue is purely for show. To date, there has not been a gasoline additive made that will clean dirty injectors. It's mcalled hype. The chemicals needed to clean the injectors would damage other parts of the fuel system, namely the pump. The only method that will clean the injectors on the car is called Motorvac, and it's very expensive.

Take care,
~Chris

PKRWUD: That's one of the most down to earth, easy to understand explanations I've ever heard about octane. I've read all the 'technical' explanations and never quite put it all together before. I've understood it well enough to select the appropriate fuel for my vehichles, but never knew enough to be able to explain it to anybody else.
THANKS.


For future reference, oxygen by itself is nonflammable. For a simple proof of this, try to light an oxy-acetylene torch without the gas turned on.

Kind of makes the NOS explosion on the F&F a little lame, huh?

Peace

SlowGT
 

Given the fact of where you are from, I doubt that you would have heard this. About 8 or 9 yrs ago, we had a really devistating flood in Baytown, home to the company Exxon. We are located right on the water. There is a plant right off the freeway that sells and transfers pure oxygen via large diameter piping run throughout the country. As the flood waters rose, so did a section of pipe that was carrying the oxygen. Once the pipe finally gave way, and the oxygen escaped, there was a massive explosion that rocked our world. That having been said, I have to disagree with you when you say that oxygen is not flammable.

Thank you very much! That is one of the nicest compliments I can ever get! I love knowledge, but I really love sharing it with people, and being able to do it in a way that most people will understand.

Thanks.

Take care,
~Chris

You're welcome. I've picked up a tip or 2 from your posts in the past.




I figured I'd have some nonbelievers when it came to the properties of oxygen. I don't know what happened in TX, but I can assure you that no oxygen burned/exploded by itself. If you had a flood around a refinery, I'm guessing there was probably some flammables floating on the water that the pipe was in. The pipe broke (causes a spark), the fuel was ignited and the presence of oxygen caused an explosion ten times worse than the flammables alone could've produced.

I'm not posting this to be a 'know-it-all', because I'm certainly not the sharpest knife in the block, but I'm pretty well versed when it comes to industrial gases. It's a huge misconception advocated by TV/Hollywood. I've got years of experience with this stuff. Why would I lie? Without being able to give you a personal demonstration, the following websites are the best I could do. They are the MSDS sheets from 2 of the 3 world leaders in industrial gases (Air Products and BOC Gases). I'm a former employee of the 3rd (Praxair) but I couldn't find one of their's.

Check out the 1st page:
http://avogadro.chem.iastate.edu/MSDS/oxygen.pdf

See page 2 here under NFPA & HMIS Hazards and page 3 under 'Fire Fighting Measures':
http://www.mwsc.com/MSDS/21.PDF

If you still don't believe me, call your local welding supply shop and ask them. Better yet, go down there and tell them you'd like to see what color is emitted when oxygen burns.

Once you believe, share it with all your buds.

Peace and safe street racing to all:)

I stand corrected. All I know is what I was told. As far as I know, that could have been a company covering up a major screw-up. I think Sec. 5 of the first MSDS sheet could have something to do with it. Thanks for the clarification.

If oxygen was flammable we'd all be dead right now. One spark and the whole world would be gone.

Not quite. Our air isn't pure oxygen. If it was, the planet's atmosphere would explode.

Oxygen in and of itself is not flammable, but it will make vitrually anything it comes in contact with extremely flammable. See the pic below. It's the label on the O2 bottle in my garage. It states clearly that it VIGOROUSLY ACCELERATES COMBUSTION.

Take care,
~Chris

Schit. Forgot the picture.

If the car is running fine with 87 octane gas but for a
stupid reason i change to premium gas (93 octane)

Am i going to notice a higher ET at the track? I just want
to know if i could be penalized for using too much octane.

I have ever tried to advance the timing to 18 and i never
heard any strange noise from the motor. (using premium gas)
I now keep it at 14. I ll certainly try to use the 87 octane rated
gas.

curious?
 

First off I understand the whole octane/power thing, so that is not what this question is about. And yes, Chris does an excellent job of explaining a lot of things. Thanks!

Out of curiosity though, are newer computers in cars able to "read" what octane is coming through the system and then advance timing if it is able to?

I ask because I remember an old episode of Horsepower TV where the two guys both were racing Mustangs. The older guy put octane booster in his tank at the track and stated that the car's computer would see the extra octane and advance the timing accordingly. Does this actually happen, or is it just TV BS?

That ability has been around for a while, and is done via the knock sensor, but very few ECM's actually take it to it's extreme. basically, the ECM has programed curves in it, and it will advance or retard the timing depending on which of it's many preprogramed curves the sensor signals are telling it to follow. If it senses a signal from the knock sensor before reaching the preprogramed max ignition advance, it will not continue to advance, and theoretically that could mean never reaching your potential. But, this is very unlikely, unless you have already advanced the timing, and are deceiving the ECM.

There are no cars in production, that I am aware of, that will just keep advancing the timing until it knocks. They all have preprogramed limits.

Take care,
~Chris

Ok I'm going to be a post ***** and skip abit of that conversation, I read what you wrote Chris and I think you explained that to me awhile back and I completly understand and not going agaist you cause I don't know the difference between my a*s and a hole in the ground when it compares to you. :D But I'm having a Mallory Distributor put in my car (351-4bbl), what should I set the timing too? More the less curious what exactly the timing does to the car, I'm hoping to get my car dyno'd so I want to set it to something reasonably good. Like is it unstable if I put my timing to something in mid 20's or just keep it at 16? And what would determine what I set it too? Like what part done to the engine.
This is the distributor I am having put in.
Mallory Distributor

I'm also having a MSD Ignition put in with it, and intake and new Holley 650 DP DF Carb too but I'm not sure if that matters.

Thanks,
sorry again if it was already asked I'm just alittle slow.... :rolleyes:

§am.

that is correct. as a matter of fact, we breath mostly nitrogen. about 70% of the air we breathe.

The ignition timing is when the spark plug fires in relation to where the piston is in it's travel. Zero degrees timing means that the spark occurs exactly when the piston reaches it's uppermost point of travel. That's no good when the rpms are going.

DO NOT BUY THAT DISTRIBUTOR!!!!!!!

Please do not waste your money on that piece of schit. Let my mistake be your gain. If you are getting an MSD box, get an MSD 8584. You're looking at about $300, +/-. TRUST ME.

I'm going to tell you right now the best way to set your timing. See, there is no single answer. Any and every mod a vehicle has done to it can affect what the timing should be set to. This is the simplest way to do it.

You will need a timing light, a tach, some liquid paper, and a vacuum gauge.

First, make sure the carburetor is adjusted correctly.

2) Remove and plug the vacuum advance hose, if it has one.

3) Mark the 10 degree mark and the tip of the pointer with liquid paper.

4) Hook up the timing light.

5) Loosen the distributor so you can turn it, then snug the bolt 1/8th of a turn.

6) Attach the vacuum gauge to a source of manifold vacuum.

7) Hook up the tach.

8) Start the engine, and check with the timing light to see where it is.

9) Adjust it to 10 degrees BTDC.

10) Check the tach and note the rpms, and check the vacuum gauge and note the reading.

11) With the hold down bolt loose, SLOWLY rotate the distributor while watching the vacuum gauge. Turn it which ever direction it is that makes the needle on the gauge go up.

12) Keep doing this until it no longer moves up. If you're not sure when it reaches it's peak, use the tach to tell you.

13) rotate the distributor the OPPOSITE direction, so that the needle on the vacuum gauge starts to drop. When it get's to a half inch of mercury lower than it was at it's peak (ie: if it's peak was 18". lower it to 17.5"), tighten the hold down bolt.

14) Check with the timing light to see where it's at now, and write that down.

Now's the fun part. Go for a test drive, and get on it. TRY to make it ping! if it does, then retard the timing one degree and test it again.

Take care,
~Chris

Chris, tell me this. I have been using Chevron Techron Concentrate in my car and customers cars for years. It works superbly. It actually corrected some running problems. How did this work without harming any injectors or any part of the fuel system? I still use it to this day.

As for dirty injectors, as far as i know, there is nothing that can clean actual "dirt" out of an injector. Maybe some other contaminents, but not dirt. If chemicals can break down dirt, say bye-bye to whatever that substance touched in your fuel system.
Motorvac is expensive, but it does work.

**** I will try to call the guy tommorow and see if he's put it in... does it suck that bad really? He said it was one of the better ones to go with that box and my engine. What problems did you notice with it? I'm more the less a stupid teenager that's learning about these hiperformance old cars so I don't notice the difference but I just want to pretty much learn, since I don't really get to drive many old cars.
The guy who is putting all this stuff in is also setting up my engine. I figured I'd leave it to the professionals. This guy is a fairly popular guy and does most old cars and I've heard only good things about him so I guess I will have to see how it goes.

Thanks,
§am.

Chris,

I think Car and Driver (or Road and Track) did some dyno testing on some knock sensor equiped cars, including the Mustang, and premium gasoline was able to get about 2-3 hp. Like you said, there probably isn't any ECM that will just keep pushing up timing. Besides, only some much timing can be added that will benefit power no matter what the octane rating. I'm sure they probably set the upper limit of timing to what is optimal for a given engine using the best available pump fuel. Our engines run best with 34 to 36 degrees of total timing so they would probably cap it at 36 if we had knock sensors, for example.

I don't know. Maybe you and your customers change your filters regularly? I know that I have seen published report after published report (check out Underhood Magazine if you get the chance, it's always got up to date info) that says what I was taught in my fuel systems class at the local cc, which is anything that cleans the injectors has to be corrosive, and anything corrosive in your fuel system will damage other parts, as well as emit emissions, and damage the O2 sensor(s). Perhaps Techron has an additive that helps to prevent some deposits from forming, I really don't know, but there are no proven studies that show it cleans dirty injectors. At least none that I am aware of.

BTW, what really kills me are these ads I see for Joe Blow's service station offering an injector cleaning for $29.95. Please.

Take care,
~Chris

I agree, but the vehicles that could benefit would suggest in their literature that the driver should run a premium unleaded gasoline.

Take care,
~Chris

Dual point distributors don't do anything for performance, but they do burn up points twice as fast and twice as often. BUT, with an MSD box, the points won't be carrying the voltage, they'll just be signaling the MSD box, so why waste the money on a dual point distributor? Mallory, for the most part, is like the K-mart of ignition parts. Their bearings wear out faster, their coils build up resistance faster than any others, but hey, they have cool stickers! :rolleyes:

Do whatever your engine builder wants, but I wouldn't use a Mallory dual point if it was given to me.

:)

Take care,
~Chris

Maybe. There is still the issue of pollution. Manufacturers may tune the cars for 94 octane but recommend 87 since it burns faster and more completely. Isn't premium something like 91 octane in CA for that very reason?

My car runs best with nonoxygenated 92 octane.

Hmm. Interesting. Yeah, I believe you're right about 91 octane out here. You've got me wondering, though. I have never seen a car that was tuned by the manufacturers for a higher octane than it was recommended to run on, but maybe that's part of the whole "California Emissions" deal. I have never seen, and doubt I ever will see, a bone stock vehicle that is recommended by the manufacturer to use 87 octane, run better with a higher octane. Never. Now, if the owner advances the timing from the stock 10 degrees to 14 degrees, then yes, it absolutely could run better with a higher octane fuel, but again, it's the mechanical adjustment that a person has to physically make, against the advice of the manufacturer, that get's the credit for the increased performance.

Take care,
~Chris

Thanks, your help is greatly apprecaited and considered cause I'm kicking myself in the a*s right now. :rolleyes: How much hp does the stickers add in performance? :D :D I will try to stop by at lunch and confirm if that is the one he (put/is putting) in and see how that goes and ask him why he thinks it's the best bet for me.

Thanks again Chris,
I'm makin' sure I ask for your advice before I do anything next. :D Who else makes good Distributors?

Check with the local Honda car club about the stickers. I think they claim a 50 hp increase PER STICKER!

I prefer MSD distributors over other aftermarket choices, but often the factory units are fine.

Actually, my top choice for a distributor would be a DON ZIG Magneto, but you can't afford one.

:)

Take care,
~Chris