The Old Octane Debate..Again

[Wess]

I was surfing around shoclub.com and came across this article again:

http://www.shoclub.com/SHO History/Shogasoline.html

Obviously it talks about the V6, but the principle argument put forth transcends any single engine platform, it was simply provided as an example.

As for myself, I am guilty of the placebo effect. I used to buy premium, but the recent surges in gas prices made me rethink my position. My rationale for buying the higher grade was always (purely an example):

"Well, premium only costs $.07 more than regular per gallon. At 12 gallons that’s only $.84 more I would have to pay in addition to what I'd pay for regular. Ahh what the heck."

So now I have discovered the strength to buy mid grade. Because...well...it's not quite premium, but not exactly regular either. I'll just sit on the fence.

Push me off the fence! What do you use in your V8 and why?

 

[Porkchop]

if your asking for purly PERSONAL examples, once winter is over and summer is back i'll start useing high test again, but for now its midgrade.

Why do you need full power with snow on the ground?

 

[KILLA]

Ive been using 91 since i bought the car, but have used my share of regular when i want to stretch my dollar. The article is convincing though. out of the several times ive used 87, i noticed no knock and no performance change. so its very possible that (although recommended by ford) premium fuel is just a waste of money, unless you have a VERY sophisticated engine perhaps w/ a turbo as it stated.

 

[jedhead]

I run preimum in my SHO. Since I have a LPM and my timing curve is more aggresive than stock timing, my car runs better on premium. My brother's stocker runs fine on 87. I can run 87 but the decreased throttle response and power is very noticable.

Bob

 

[SHO#7]

In my past 96 I would have spark knock on 87. I could get it by giving the throttle a quick "goose". It never set a knock sensor code, so I have no reason to think that it did not work. On 93 octane it would not do it. So I ran premium. The only thing that I can think of, was the car had had a cam noise, and maybe when the previous owner had it welded, the sprocket was off just enough to change the time?

I run nothing but premium in my 98 ( since new ) and the same goes for me 93 ( have lots of fuel reciepts from the previous owner ). My Maxima says to run at least 91 too. So I do ( since new )

Mike

 

[NJSHO]

I noticed a difference when I used regular for a while. When I was on the highway next to a dividing wall and gave it gas I could hear the engine pinging.

 

[Ian Macoomb]

I've been running 87 for the last 5 years.

However, my car now pings on anything less than 91 with my Xcal tune. I need to play with the timing a bit and replace my failing FPR.

 

[Fourcats]

Yip, we all need them "chews"...

I run Chevron Supreme, for that extra little bit'o torque at low RPM. And I believe Mike{shopartsnw}

 

[MilTownSHO]

All my SHO's have run fine on premium.

My 92 that had cams I would run premium for obvious reasons.

On my mom's 98 she swears she gets worse gas mileage with anything but premium, so that's what she runs.

On the SRT-4 I run only premium but that's because of the turbo. The manual even says you can run regular and the computer will adjust (aka less boost)

 

[roland]

i use 89 cuz it's a lot cheaper than either 87 or 91, but if the ethanol mixture gets under 2 bucks then i'll usually spend the extra 20 cents on the 91

 

[Mr Anonymous]

Run the lowest octane you can that doesn't ping. It's that simple.

It is pure myth that so-called "premium" fuel makes more power. In fact, higher octane fuels produce LESS power since they are less combustible and don't burn as efficiently as lower octane fuels. The only time premium will add power is if you've got mods to the car such as tuning that change the spark timing and fuel.

Mid-grade is probably the biggest rip-off of all since it makes those people who don't want to spend extra on premium but want to feel like they're doing something special for their car feel good about themselves.

Everyone running premium for no reason other than it makes them feel good, start running regular and take that ~$250 or so a year you've been wasting and invest it in oil company stocks so you can reap the benefits of the ignorant people who still use premium!

 

[NoSlo]

Octane - only for knock resistance

For a daily driver V6, regular pump gas works just fine (many miles of personal anecdotal evidence). If detonation occurs on the lower octane fuel, the knock sensor will retard timing and the computer will learn any adjustments that might be needed. The difference in fuel cost far outweighs any difference in fuel efficiency, if any. Only for the last percent or two of performance is premium fuel useful.

One advantage to premium fuels is, depending on the vendor, they will also have additives like Techron, so you don't have to use a bottle of fuel injector cleaner as frequently. The only cheap fuel to watch out for is that with ethanol added - you get fewer miles per gallon from ethanol than from regular gas (which is added as an inexpensive octane improver), because there is less energy from the chemical reaction in burning ethanol. It can actually end up costing you a bit more per mile in the long run.

Because of the efficient combustion chamber design (centrally located spark plug, four valves, etc) and electronic ignition, knock is not a big issue in the SHO. It has been alluded that the Yamaha-built engine has better combustion characteristics than Ford engineers had anticipated.

For more fun facts: In general, brand new engines without carbon deposits causing hot spots or increased/unbalanced compression ratios can use fuel with an octane rating several points lower than even regular pump gas, without any knock. Manufacturers design their engine management systems to use pump octane after the engine is broken in to normal operating conditions, where typical combustion chamber and valve carbon deposits require more detonation resistance.

Therefore, if you have noticeable loss of power from running lower octane, this is probably from the ECU detecting knock and retarding the timing due to abnormal combustion chamber deposits causing detonation. You might consider cleaning or replacing spark plugs, or doing a de-carbon procedure on the engine with Seafoam or hot water if the butt-dyno feels different on regular fuel. Other tune-up factors, such as a weak or dirty fuel injector causing one cylinder to be leaner, can also cause ping.

 

[wuzzzer]

I usually use mid-grade around 90, 91 octane. There's a gas station next to where I work that sells mid-grade for the same price as regular grade.

If I run regular and then switch to premium, the car seems to pull ever so slightly harder just before redline.

 

[SonicRiot]

Often, new Porsches run 87 when they roll off the lot. I have yet to use 87 in my Jag, but I've used it in my SHO. My mother's 2003 3.5 Altima says 87. And it's quite powerful.

The issue is that the RISK of detonation is bad. With a newer vehicle that is under warranty, the owner must be careful. Use of less than recommended gasoline may void some warranties.

There's got to be a way to run efficiency tests or map out a knock sensor for comparison of high-test vs. decaf.

Anyone?

 

[NoSlo]

More fun to know Gas secrets

The big 'secret' - all gasoline is basically the same!

Consider:

• Due to emissions laws and the importance of fuel in the national economy, the federal government very tightly regulates the chemical composition of the different molecules that make up pump gas, and the additives used for octane enhancement and deposit reduction. This means the fuel produced by different refineries is essentially the same. There is no secret ingredient between brands when fuel is refined and manufactured.
  
• Fuel is distributed through a massive network of common-carrier national pipelines, which are independent of the individual fuel companies. Even though it might take 14 days for fuel to travel from the Gulf coast to New England, for example, fuel is distributed on spec through this fungible system. This means that an oil company has a contract where they can put in 60,000 barrels of 87 octane on one end of the pipeline from their refinery, and immediately take out 60,000 barrels of 87 octane on the other end for distribution, even if the fuel they take out wasn't even manufactured by them.
  
• Different grades of fuel are sent through the same pipe in batches. The different grades used to be seperated by 'pigs', basically plungers that were sent through the pipe to keep the different fuel seperated. Now computers know how long it takes for the fuel to travel, and batches of different fuel run continuously through the pipes and are seperated back out at the other end by computer, with some mixing of the grades allowed between the batches when the switchover takes place. When diesel, jet fuel, and other incompatible products mix in the pipeline during these batch switchovers, this trans-mix is then sold off for other purposes.
  
• The 'branding' of gas comprises of brand-specific additives such as Techron added to 91 octane Chevron, that are introduced at the distribution terminals. Even these aren't much more than the standard deposit reduction chemical additives, due to federal regulation.
  
• Even though gas stations might sell three different octanes, sometimes the middle 'plus' grade is just a mixture of regular and premium. Depending on the company, the delivery truck often just has two tanks and the middle grade is mixed right at the gas station. Can you mix your own regular and premium together cheaper? Maybe!
  

Oh, and octane boosters in a bottle don't do squat.

 

[NoSlo]

There's got to be a way to run efficiency tests or map out a knock sensor for comparison of high-test vs. decaf.

Anyone?

About the only way test without a laboratory is to disconnect the knock sensor and see how much knock there is without this input to the ECU.

The knock sensor is a piezo element, that works like a microphone tuned to the 'ping' resonance frequency that detonation makes. Think tapping on the engine block with a ball peen hammer and the 'tink' sound that comes out. The signal is then analyzed by the ECU against maps based on engine load and rpm, probably with sophisticated analog to digital converters, to figure out what is detonation and what is not. One could even imagine, since the sensor is in the center of the block, that compensation could be applied to increase sensitivity for detection of the cylinders that are farther away from the mounting location of the knock sensor.

Anyway, the signal out of the sensor is not just an on-off signal. To begin to analyze it, you would need a data-capturing oscilloscope, along with some very repeatable lab conditions with a dyno and throttle control and engine block temperature monitoring to compare 87 octane to 91 octane (or even 100 octane for a 'no ping' baseline).

 

[SHOZ123]

I think a lot has to do with the local quality of gas in your area. i have never had a problem on any car I've had in the last 25 years with pinging. But all the gas around me has a 10% ethanol mix which is very good for the pinging issue. I use 87 octane exclusively even on the 93 octane tunes I have. Still going to California last year using 87 octane out west was not a problem.

My plan is to play with the timing tables until I do get some ping then back off a bit.

Bottom line is if it ain't pinging then go down an octane grade if you can.

 

[1slickRED89]

if you care enough to ask, then you should follow the manufacturers specs and recommendations. Alot of testing goes into that recommendation, lots of painful, repetitive and expensive testing.

On the other hand, if you where to do a cost Vs. torque comparison, dollar per gallon Vs.Tq with a safe calibration. I would think that a modest calibration and cheaper fuel would be the better value, but with slightly less Tq. who wants 'slightly less' torque anyway?

try this on for size, in my Jeep, I try to achieve the exact opposite result of high octane fuel, the more volatile and lubricative the better. better what? MPG and Tq.

 

[stephen newberg]

Chris is right for the Gen III SHO, run the lowest octane you can that doesn't ping. When I first got the car forever ago I did a bunch of testing for performace and milage differences, and basically, there are none above the level of statistical noise. As a result, I have been running 87 octane regular ever since, with no negative effects, and at about a quarter less a gallon, since 1998, that is a lot of money still in my pocket. Many posters here have gotten into the Gen III SHO to get a high performace sedan at very low prices. No sense wasting money after that on premium gas if you do not have to. Instead, put those saved funds toward better tires or suspension mods, after getting your cams welded, of course.

pax, smn

 

[Mr. SHO]

In the winter, I usually get by just fine with 87 in virtually all traffic conditions. In hotter weather when I'm dealing with stop and go traffic, the 87 causes detonation and a subsequent lack of power from the PCM pulling out spark advance to eliminate the detonation. 87 is still fine for highway trips even when it's really hot out, but when the underhood temps get way up there (slow traffic or racing light to light) performance suffers. Midgrade (89) is usually enough to make the ping stay away in the summer. This is all for stock programming... with the Apten tuning, I need 93+ even in the dead of winter.

Observing detonation on the V8SHO is not like listening for pinging on an older motor though... the PCM seems to correct the timing relatively quickly, so you don't hear the pinging unless you are really listening for it. On your older pushrod motors, even your half-deaf grandmother would know when the engine was pinging. Not that she would do anything about it...