Higher octane...higher HP?

[HudsonValleyTitan]

This months R&T has an article in its' TECHNICAL CORRESPONDENCE that says it all. A reader writes in that he heard that his 04 Accord will have a 10HP boost if he used premium fuel, and wanted to know if this was just a "pipe dream". The vehicle can be any newer vehicle using a knock sensor according to the article. Here's their answer:


""This one is for real. Modern electronics is good enough that automakers are now writing engine-management software to "follow the knock sensor." That is, the ignition timing, which is already being adjusted by the engine management computer many times per second, is largely determined from what the knock sensor is commanding.
In practice, this means the computer is often advancing the ignition timing (for better power and fuel economy), while the knock sensor announces when the timing is too far advanced whenever knock is detected. Then the computer retards the timing a couple of degrees and the process repeats. Everything else being equal, the higher the fuel octane, the more ignition timing can be run before knock occurs, and thus more power is made. Because the system is constantly at work and finely adjustable, it accounts for the various fuel blends that end up in the cars tank.""

But some of us already knew the benefits of using premium.

[smoothTitan]

i use premium, and get better mileage with it. some say no but i have drove the same path of 160 miles every other week for 2 yrs, and i have tried 87,89,93. the 93 gives me more mpg to doubt about it. i dont know about the hp, to hard to make a call on.

[Treebasher]

I've always enjoyed this article on the subject of octane. It's long but well worth the read.

It's tough to believe that high octane gas, that takes more compression to detonate, would give more power. But electronics have come a long way...

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What's the difference between premium and regular gas?

08-Oct-2004

Dear Cecil:

In this time of high gasoline prices, the Teeming Millions need your guidance (well, at least I do). What is the difference between premium and regular gas, and is this difference worth the extra money? I normally put premium gas into my car because I don't mind paying two or three extra dollars at the pump. Am I being scammed by the gas stations, or is the benefit to my car worth it? --Jeff, via e-mail

Cecil replies:

Not to introduce a radical concept, Jeff, but have you tried reading your owner's manual? If it says to use premium, my advice is to use premium. If it says regular, use regular. The fact that your note indicates no acquaintance with such matters suggests that you may in fact be a scam victim, assuming by this you mean "someone who believes what he hears in commercials." I have a hard time working up much outrage over this deception, since discovering the facts requires so little effort. If you don't mind paying the extra money for no reason, don't expect the oil companies to suffer any pangs accepting it.

In most of the U.S., regular gas has an octane rating of 87, midgrade gas is 89, and premium is 91 or 92. (Octane ratings are lower in the mountain west due to the effects of thin air on internal combustion.) Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.

The majority of cars are designed to run on regular gas, and that's what the manuals tell the owners to use. Higher-performance cars often require midgrade or premium gas because their engines are designed for higher compression (higher compression = more power), and regular gas may cause knock. If your car needs high-octane gas, the manual will say so.

Using high-octane gas in a car designed for regular accomplishes little except more rapid combustion of your money. Some refuse to believe this, claiming, for example, that premium gives the family Toyota better mileage or more power. These people are on drugs. Others say premium is purer or contains detergents that will cleanse your engine of uncouth deposits. Likewise misguided thinking--government regulations require detergents in all grades of gasoline. (BP Amoco, I notice, asserts that its premium gasoline contains more detergents than legally required; if you think that's worth 20 extra cents a gallon, be my guest.) Some automotive types claim that using premium in a car designed for regular will make the engine dirtier--something about deposits on the back side of the intake valves. I've also heard that slower-burning high-octane gas produces less power when used in ordinary cars. Believe what you like; the point is, don't assume "premium" means "better."

Occasionally you get some genius who takes the opposite tack--he spends an extra 10 or 20 grand buying a high-performance car, then decides he's going to save three bucks per tankful using regular instead of premium as specified. He figures as long as the engine doesn't knock he's OK. Wrong, carbon monoxide brain. Car engines nowadays contain knock sensors that detect detonation and automatically retard the spark to compensate. The delay means maximum gas expansion occurs when the piston is farther along in its downstroke and thus there's more room in the cylinder head. This reduces peak cylinder pressure, eliminating knock but also giving you less power and poorer mileage.

You may ask: Don't knock sensors make it hard to tell when an old car needs higher-octane gas? Years ago, when your beater started pinging on grades or under acceleration, that was the sign that carbon had built up in the cylinders, increasing compression, and it was time to switch to high-test. Now the knock sensors compensate, which seemingly might conceal the problem. Don't fret--today's fuel injection systems precisely meter the fuel-air mix, resulting in fewer unburned hydrocarbons and less carbon buildup. If you're still concerned, I'd say it makes more sense to spend $6 on a bottle of carbon clean-out juice than an extra $150 a year on high-priced gas.

[MaxPowers]

Interesting article. I've always used 87 octane on my truck and have never had any problems. The manual states 87 and that is what i go by. I'm not about to spend extra money on something that isn't recommended.

[miketan]

I've been using premium lately and I've found that the engine is more responsive in light throttle conditions. With the 87 crap, throttle response was a little more sluggish than it is now. If only we could figure out a way to defeat the torque management software in the PCM.

On my old daily driver (Toyota 22r PU), I used to run 89-octane because I had the timing a few degrees advanced over stock. Big difference in performance compared to running 87-octane/factory timing on that truck. Once I tried 91-octane, but it didn't seem to do anything more performance-wise than the midgrade. Maybe the rather low 9.3:1 CR had something to do with it.

I'm not sure what the big fuss over using premium fuel on the Titan is all about. We all know the computer pulls the timing, to some degree, from the total spark advance if you use regular. Yeah, it'll run just fine without premium, but it won't be quite as responsive.

[Justintoxicated]

it can possibly make less power, although it can also make the engine run cooler, so there is less power loss from heat. But everything on the Titan is regulated electronicaly, so there is chance it may run better on premium because it can advance the timing slightly. Not worth the extra 25 cents a gallon to me though. Fuel is expensive enough, and the compression in the Titan is obviously not enough to REQUIRE a high octain fuel, so the benefit of running it diminishes some. You probably would not see any significant improvements anyways unless your talking about 110 vs 91 or such, and I'm not sure that the titans system could even adjusting the timing to advance that much.

I run 111 in my ATV because I raised the compression by changing the doms to smaller ones in the head, I also advanced the timing using a timing plate. it does give it a bit more power and it smells really good when it's burning . However putting too high octaine in it can reduce HP. I prefer to run it mixed so I have about 100 oct since I really don't NEED 111.

It's hard to say if the Titans electronics advance the timing enough to notice significant gains. But I have heard a number of people say it does improve performance. I find it hard to believe. I hear the same thing when people put race gas in their ATV's usualy this is an indication to me that there carbs are jetting too lean, and the power increase is coming from keeping their motor cooler (better suggestion wouto re-jet and run normal fuel)

The Titans system is regulated electronicaly but it would make the most sense to run regular fuel IMO.

BTW Race Fuel 111 etc is less combustive than premium just as 91 is Less combustive than 87

[SuperT]

When I talked with my service manager a week ago about the brake fix, he told me that and one other question were the two top on his list. The other question was: "Can I run gasohol/ethanol in my Titan?" (fuel blended with distilled alcohol). Ethanol is much cheaper than gasoline and readily available here.

While the ethanol may have octane ratings as high as 100, the owner's manual only makes a minimum octane recommendation, and doesn't specifically address the use of ethanol. I believe that minimum octane rating is in the 87-88 range? Someone feel free to clarify that. He said Nissan didn't recommend the use of alcohol blended fuels.

[rcflier_97]

I have run 87 in all my cars except for a 69 Olds 442 (when leaded gas went out the window I had to burn 93 with a lead additive). Like the article said, if the manual does not specifically say 93, stay with 87. The on board systems compensate even if you are wasting your money using 93. IMHO

[cttitan]

Originally Posted by HudsonValleyTitan

This months R&T has an article in its' TECHNICAL CORRESPONDENCE that says it all. A reader writes in that he heard that his 04 Accord will have a 10HP boost if he used premium fuel, and wanted to know if this was just a "pipe dream". The vehicle can be any newer vehicle using a knock sensor according to the article. Here's their answer:


""This one is for real. Modern electronics is good enough that automakers are now writing engine-management software to "follow the knock sensor." That is, the ignition timing, which is already being adjusted by the engine management computer many times per second, is largely determined from what the knock sensor is commanding.
In practice, this means the computer is often advancing the ignition timing (for better power and fuel economy), while the knock sensor announces when the timing is too far advanced whenever knock is detected. Then the computer retards the timing a couple of degrees and the process repeats. Everything else being equal, the higher the fuel octane, the more ignition timing can be run before knock occurs, and thus more power is made. Because the system is constantly at work and finely adjustable, it accounts for the various fuel blends that end up in the cars tank.""

But some of us already knew the benefits of using premium.

But our knock sensors do not normally retard the timing according to the service manual...

This is what the service manual has to say about the knock sensors in the Titan.

The knock sensor retard system is designed only for emergencies. The basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition. The signal is transmitted to the ECM. The ECM retards the ignition timing to eliminate the knocking condition.

[GETSOMZ28]

The 10hp gain on the Accord is even mentioned in the owners manual (however, we still run 86 octane in ours).

This wont will work with all vehicles. If a cars computer is tuned to run max timing on 87 octane, then it will not benefit from higher octane fuel.

[FluxCubby]

Might want to check out page two of this thread . There was a brief discussion on premium fuel, and higher HP. I thought that buying premium was just a waste of money. Others thought that the Titan's timing would advance giving you more HP. Same sort of deal as here. This is all very interesting to me. Even if I could get more HP out of the truck, it's not worth $0.25 / gal IMHO.

[VShortt]

Its been said that high octane fuel is the only reason that the QX56 is rated at 315hp where ours is rated at 305hp. Who knows.

[KTMNealio]

You would need a higher compression ratio to take advantage of the higher octane fuel. Just advancing the timing a little isn't going to make much difference.
- Nealio

[FluxCubby]

Well, that's what I thought. But I'm no master mechanic. I just know from what I read. I sure would like some hard data on this, though...

[HudsonValleyTitan]

Originally Posted by KTMNealio

You would need a higher compression ratio to take advantage of the higher octane fuel. Just advancing the timing a little isn't going to make much difference.

- Nealio

Not true. High compression engines REQUIRE premium fuel, but lower compression engines will benefit from premium use if they have a knock sensor...as explained.
Also, someone mentioned needing higher compression to ignite premium fuel. Also not true. This is diesel you're talking about. Gasoline is spark ignited, it's not ignited by compression.
I just found the article interesting and backs up what I've said all along......the titan (as do most any current knock sensor controlled vehicle) has more get-up-and-go while using premium fuel. It's up to the user to decide if it's worth the extra .25-.35 cents a gallon.