It has to do with smog regulations.

What's really pathetic is that we Californians pay the most for the least. The highest I've paid so far is $3.48/gal. for 91 octane. The Z has been pinging a bit on this reconstituted camel ****, so my last fill up I put in five gallons of 100 octane at $5.90/gal. for a grand total of exactly $75.

"Premium" 91 octane: 12.362 gal. @ $3.479/gal. - $43.01
100 octane unleaded "Race" gas: 5.423 gal. @ $5.899/gal. - $31.99

On the plus side, it took care of the pinging.

 

You're not getting the least, you're getting cleaner air.

Ken

 

Are you running mods? turbo maybe? Sucks about the ping.

 

Until I get pissed and start running leaded race fuel

 

Nope, stock '06 with 5,000 miles. It's noticable in the 2000-3500 RPM range, even in low gears and small throttle openings (<25%, i.e. low loads).

I imagine 92 or 93 octane is the real-world minimum if you don't want to live on the knock sensor. I wanted to bump the octane to see if that was indeed the problem. According to my math, my mix was a bit better than 93 octane. So far, so good.

There's also the remote possibility the problem is the brand of gas I've been using (Mobil exclusively, company card), so my next experiment is a full tank of 76, Chevron or Shell 91.

My apologies for veering completely off-topic.

 

Eight people put 87 in their Z? Shame on you! go sell your car and buy a Honda!

 

i just use Regular and it works the same. the dealer told me when i picked up the car that you can use any grade as long as its not diesel. its all a marketing scam anyways he says. so far i have 1600 miles on my car and no problems at all with 87oct.

 

Premium only.. the manual said so and I want to keep my car as long as I can.

 

+ infinity! for the love of god people, please use premium!

 

i've found that i ping on Shell 91. they like to use different formulas for winter/summer driving here in CA.

91 Chevron
91 Mobil or
91 76 only for me... (and the occastional 100+ race gas. heh)

if you can't afford the gas, then stop drinking $5 cups of coffee @ starbucks.

 

Premium is only 20 cents more regardless of how much gas prices are. I don't understand why people think that because gas prices go up, they shouldn't put premium in their cars...

 

you don't sh&t all over your house so don't **** all in your car.....USE F***ING PREMIUM

 

93 here. Have run every tank with 93 except 1! As has been said many many times in this thread, premium is ONLY 20 cents more than regular. That is $3-4 more for a tank to use premium. I thin the choice is quite obvious.

 

That might not be ping because pinging usually happens around 4000-6000 rpm. Plus your N/A and the ecu should retard timing, unless you have a reflash which advances your timing.

BTW I hate the fact that we pay so much for 91 octane. I don't even think Nissan made the 350z to run on 91. My 91 Mr2 turbo from a few years back was built with 98 octane in mind. So using 91 made the ecu retard a lot of timing. I hate these damn prices but I will always pump premium.

 

I've been working on cars for better than 15 years. I know what detonation sounds like, and it can happen at almost any engine speed given the right conditions.

Remember, the knock sensor has to "hear" the ping before it can act. I can hear it too.

Exactly my point. Even with aluminum heads and fuel injection, 10.3:1 is a fairly high compression ratio for a street car running on pump gas. That's why GM uses reverse-flow cooling (started with the LT1) on their higher compression engines. (For the uninitiated, coolant from the radiator is routed through the heads first, rather than the block.)

I honestly don't know how the forced induction crowd gets by with stock pistons.

 

Shell premium EVERYTIME!

 

Your car is a temple, so put in the good stuff.
BY LARRY WEBSTER
August 2005


At a local Mobil station, a gallon of unleaded regular gas goes for $2.15. Drive a mile down to the nearby superstore that sells everything from apples to swimming pools, and it's $2.10 a gallon.

Supposedly, the superstore buys gas in such large quantities that it gets a volume discount for what is essentially the same product as the name-brand stuff. The Mobils and Chevrons of the world say they include costly additives and detergents that keep your engine free of deposits and make your car perform better. So what's the truth?

To find out, I paid a visit to Andrew Buczynsky, GM's fuel guru. He says that with gas, like almost everything else, you do get what you pay for. Buy cheap fuel, and you risk coating parts of your engine with thick deposits that can dramatically affect your car's performance. There are a number of possible conditions including sticky intake valves and clogged fuel injectors.

Choked injectors distribute fuel unevenly, so instead of having a well-mixed brew of gasoline and air entering the combustion chamber, you get an intake charge with pockets of too much fuel and alternatively lean portions. If there's not enough fuel around the spark plug when it sparks, then you don't get the usual combustion that drives the piston downward. In technical terms it's known as a misfire.

Every engine misfires now and then, but misfires usually occur so infrequently that the driver never notices. The car's engine computer knows what's up, though. When the frequency of misfires reaches a certain point, the computer raises a red flag and turns on the "service engine soon" light on the dash. Uh-oh, we know what that means—a dreaded trip to the dealer. Ignore the light, and the misfires may get frequent enough that the car feels sluggish.

The repair for this type of problem depends on the severity of the deposits. In mild cases, the technician may be able to simply scrape clean the fuel injectors or sometimes a bottle of fuel-injector cleaner will do the trick. In some cases, though, the fuel injectors will have to be replaced. If the deposits have formed on the intake valves, then you're looking at a cylinder-head rebuild. The cost of the repair will depend on the severity of the problem and whether your car has a warranty in effect. The worst case, however, could mean a bill of more than $1000.

Buczynsky says the exact cause of engine deposits is not known. Gasoline contains over 200 different molecules, and so far, no one has isolated a particular brew that is more likely to cause engine deposits. GM and other manufacturers, however, noticed there were regional concentrations of fuel-system warranty claims and traced the problem to the fuel.

Gasoline is gasoline whether you're in Florida or California, right? Wrong. There are different concentrations of elements like sulfur, for example, that change the chemical composition of a batch of gasoline.

Since it's not known what causes these deposits, gasoline retailers can't be penalized for selling defective fuel. So to keep the deposits from forming in the engines, you need detergents added to the fuel.

But how do you know which brands have the right kinds of detergents and additives to keep your injectors clean? Until recently, that was a tough question to answer, but in 2004, representatives from BMW, General Motors, Honda, and Toyota got together to specify what makes a good fuel.

They called their agreed-on standard "Top Tier" and published it for the various gasoline retailers to voluntarily meet. So far, eight companies currently sell gas that meets the Top Tier standard. You can read about them at www.toptiergas.com. At some point there will also be a Top Tier logo on the pumps like the one pictured here. For a company to receive the Top Tier seal, it has to certify every grade of fuel, not just the high-octane stuff.

 

TOP TIER Detergent Gasoline Retailers

Gasoline retailers must meet the high TOP TIER standards with all grades of gasoline to be approved by the automakers as providing TOP TIER Detergent Gasoline.

In addition, all gasoline outlets carrying the brand of the approved retailer must meet the TOP TIER standards.

Additional gasoline retailers are added to the TOP TIER list as they meet the standards. The retailers known to be on the TOP TIER list are shown below.

TOP TIER Gasoline Retailers:

QuikTrip
Chevron
Conoco
Phillips
76
Shell
Entec Stations
MFA Oil Company
Kwik Trip/Kwik Star
The Somerset Refinery, Inc.
Chevron-Canada
Aloha Petroleum
Jiffy Mart
Mahalo
Tri-Par Oil Company

 

Special Reports

Do You Really Need Premium?
And Answers to Other Gasoline Questions
By Philip Reed
Email | Blog
Date Posted 07-05-2005
Buying premium gas is like taking vitamins — you can't always feel the difference and yet you know it's the right thing to do. But as gas prices climb, paying the extra dime per gallon for premium is like adding insult to injury. Eventually, the thought is bound to jump into your head: do I really need to pop for premium?

Until about 15 years ago, if a car called for premium gas and you pumped in regular, the car began to knock and ping and even vibrate. But that was before they essentially put a laptop under the hood of the automobile, said Dr. Loren Beard, senior manager of Environmental and Energy Planning, for Daimler Chrysler. Now, sensors take readings and tune the engine as you drive by adjusting the timing for whatever fuel you put in the tank.

The result is that a car that calls for the midgrade gasoline will usually run on regular without knocking, Beard said. However, its performance will suffer slightly. How much? It will be perhaps a half-second slower going from zero to 60 mph.

Volvo cars call for "premium fuel [91 octane or better] for optimum performance and fuel economy," said Wayne Baldwin, product/segment manager S60/S80. "However, there is absolutely nothing wrong with using 87 octane as the knock sensors and engine management system 'protect' the engine from knocking."

Baldwin, a former rally driver who competed in SCCA Pro Rally events said that engines have changed a lot in the past 15 years. "Cars built before 1990 probably do not have knock sensors and many brands back then relied on high-compression ratios for the best performance. Today [performance comes from] electronically controlled spark curves, turbos, variable valve timing, supercharging and knock sensors."

Issues of performance aside, Baldwin said you should never use gasoline that causes your car to knock. "Constant knocking or detonation is a real bad thing for engines," he said.

When choosing what grade of gasoline to use, Steve Mazor, principle auto engineer for Auto Club of Southern California, said it is important to read the owner's manual carefully. The key is to figure out whether premium gasoline is "required" or "recommended." If it is recommended then a driver could opt to use a lower grade of gas, if they were willing to accept slightly reduced performance and fuel economy.

However, Mazor added, "We don't recommend that people switch down. Let's say you switch down to regular, and you have to accelerate to avoid an accident and it doesn't accelerate fast enough. The Auto Club can't be responsible for causing that situation."

Edmunds.com has a Volvo S40 in its fleet, so we consulted the owner's manual to see the exact phrasing in regard to fuel requirements. It said, "Volvo engines are designed for optimum performance on unleaded premium gasoline with an AKI (Anti Knock Index) of 91 or above. The minimum octane requirement is AKI 87." It appears that Volvo is making a recommendation for premium gas but is not requiring it.

In Edmunds.com's Forums debates abound over the pros and cons of using different fuel grades. One member even suggested there was only one type of gasoline, no difference — except for price — between regular and premium. Other members recommended using premium gas even if the manual called for regular. We put this question to Mazor and Beard.

Mazor: "All this does is do a very good job of draining your wallet. People used to put in a tank of premium to get 'the good stuff' to help their engines stay clean. But now they put detergents in all grades so it doesn't really get you anything."

Beard: "If you have car designed to run on 87 [octane], it doesn't help to run it on higher-octane-level gas. But there are several exceptions." He said that the 3.5-liter Chrysler engines are designed to run on midgrade gas (89 octane) and it allows them to advertise a certain peak horsepower. However, it will run well on regular gas. "The difference is very small," he said.

Interestingly, Mazor noted that at some gas stations, there are only two grades of gas. However, they blend the regular and premium at the pump to produce the midgrade gasoline. This allows them to have only two underground tanks for the gas storage.

In Edmunds' forums some drivers expressed concern about the quality of gas sold at independent gas stations and advised sticking to the so-called "name" brands of gasoline.

"Typically the only difference is the additive package they put in the gas," Beard said. The additive package is often put into the gas as the tanker is filled up at the refinery. A common additive is a detergent agent. "The law requires a certain level of detergents in gasoline. Shell for example is putting in more detergent — whether that has a measurable effect to the driver is debatable."

Detergents have a marked effect on engine deposits. "If you take apart a modern engine that has been running on a modern fuel, and compare this to an old engine that was running on old gas, you can see an obvious difference," Mazor said.

The biggest difference between today's gas and the gas sold 15 years ago is the removal of lead. Taking out the lead, and developing effective catalytic converters to more completely burn emissions, have radically cut pollution.

The major oil companies each have a magical-sounding name for their gasoline and tout its superiority over other brands. The difference is the additives or the amount of detergent added to the gas that comes from the refinery. The benefit of these additive packages is lost to most drivers who simply fill up at the gas station with the cheapest prices or the one for which they carry a credit card.

Does a gas expert like Beard have a preference when buying gas? "I just watch the light on the dash. After it has been on for a day I get nervous and go to the closest station available."

 

Well you've heard from both sides of the spectrum. Someone is always going to be an EXPERT and always have an OPINION!