Fuel ????

[RONDAL]

Re: Fuel ????

Increase the compression ratio - Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline -- their engines are using higher compression ratios to get more power.

[RONDAL]

Re: Fuel ????

Cars that require higher octane gas actually need that higher priced gas because the engines compress the fuel more before it ignites it. If you put regular gas in a car that requires premium, the gas will prematurely ignite when it’s being compressed and the engine will give you a knocking sound. This is bad for your car.

Chemists perk up…
For all you burgeoning chemists, gasoline is basically octane and heptane, or hydrocarbon chains that are 8 (octane) or 7 (heptane) carbons long. Octane simply can be compressed better (i.e. without the exploding part, at least at the same levels of pressure) than heptane. An octane rating of 87 means it’s 87% octane.

It’s a “rating”…
The reason why higher octane is more expensive is because it’s harder to refine the gasoline so that it contains more octane. Now let’s add another wrinkle… the octane is actually an octane rating, or it behaves as gasoline with that percentage octane would behave but might not actually have that much octane in it. While that doesn’t really matter, it does mean that the gasoline you use could have a mix of other things in it (still real gas though) to give it properties of a higher octane without actually having more octane. Does it matter? I don’t think so but I write software for a living.

[James]

Re: Fuel ????

your buddies modified rabbit is modified...they are talking about stock cars.

If we're talking high-preformance cars then you'd be a moron to use anything less then they reccomend but this is a ~$30k commuter car we're talking about.

My mom ran 87 in her volvo (s70 turbo) for 4 years in calgary with 0 problems...and they reccomended 91

edit: ZOMG link to the article next time :P

[RONDAL]

Re: Fuel ????

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."

[RONDAL]

Re: Fuel ????

your buddies modified rabbit is modified...they are talking about stock cars.

If we're talking high-preformance cars then you'd be a moron to use anything less then they reccomend but this is a ~$30k commuter car we're talking about.

My mom ran 87 in her volvo (s70 turbo) for 4 years in calgary with 0 problems...and they reccomended 91

uggggghhhhh you dont read do you. sure you can run 87...and it will run, but not the way it was intended to. If you wanna pay $40,000 for a 180hp car and only get a small % of that power cause the ECU is retarding your timing go ahead.

I thought this was a car enthusiasts forum not a penny pinching sunday granny driving forum.

[RONDAL]

Re: Fuel ????

so how much power do you actually lose?:


Can I Save Money and Run Low Octane? Wrong!
Here is a dyno chart showing two different cars. When I dynoed one of these cars, I knew that something was immediately wrong! Guess which one?

Notice that the 89 Octane car's power curves are very jagged. This is a result of the car "hearing" knocking and pinging and desperately trying to adjust the timing and save the engine. The ECU is almost searching for the best advance and having quite some trouble, not good.

The stunning results of running the lower grade fuel are -22 ft/lbs and almost -19 HP!!!! Ouch!

Folks, don't abuse the knock sensing capabilities of you beloved car. Let's just stick to the good stuff!




thanks but i will stick to putting what is recommended in my car

[James]

Re: Fuel ????

it is a car enthusiasts site...and they are talking about stock cars...do you really think people who even ask this question care if their car puts down 7 less horse power to the wheels running 87?

no...they dont...or they wouldnt be trying this in the first place.

if you want preformance out of your car, be it a 89 hyundai or a 2006 db9, you run the highest octane you can...but this thread isn't about 'how to get the most out of your car' its 'how to save money on gas'

[RONDAL]

Re: Fuel ????

if we are answering that:

a) walk or bicycle
b) take the bus
c) by a toyota tercel

im merely trying to clear up a completely misleading initial post by someone who posted this information on a CAR ENTHUSIAST site. if i wanted misinformation and people talking nonsense on topics they have no clue about i would go hang out in the mk4 forums on vortex.

[James]

Re: Fuel ????

So..was the dyno on the chart above done @ 3500 ft + above sea level? Because the OP is saying this contributes to why it works...so if it wasn't then you're not dis-proving anything.

I dont even think VWSM would disagree that there isnt SOME decrease in preformance but he says 'for the regular joe can save a few bucks'...

remember, a LOT of the people who read these forums arent enthusiasts, they are people who have questions about their car, type 'Volkswagen websites + canada' or somthing into google and find their way here...and for those people, who arent concerend with the preformance of their car, how is this not useful?!

While I don't 100% agree with the origonal post, i do agree that in MANY circumstances this could save people a few bucks on gas...nobody's holding a freakin' gun to your head at the pump and forcing you to use regular gas..and it WONT blow up your car..so whats the harm in trying it out if you're 90% of drivers on the road who would rather see cash in their pocket than numbers on a dyno?

[Khyron]

Re: Fuel ????

All that google-quote you posted does nothing to contradict anything posted. I know exactly how detonation is caused.

Here's the point you need to disprove:

Assume a car gets detonation with 87 at sea level, and retards it's timing by 15 degrees. Take that car to 3500 feet, and the detonation will be reduced because of the reduction of air density. It probably won't even ping at all. This is why NA engines produce LESS POWER at elevation. Less power because of less compression. Less compression means you don't need as high an octane.

My objection to the original posters claim, is that while a NA car (like the 2.0 or the 2.5) will ping less at altitude, an FI car (turbo or supercharger) compresses the air charge to a certain PSI. Even at elevation, there is some loss in density but not nearly as much as a non-turbo car.

So back to my simple example: if the car was down 15 degrees with 87 at sea level, at elevation it might be 3 or 5. But if it was a turbo vehicle, there would still be less retard, but more like 9-11.

End result is I wouldn't run a lower octane on a turbo car without logging it.

Khyron

[100%VAGitarian]

Re: Fuel ????

i wish i had made it to the meeting but...anyway, hate to butt in on this heated debate but, i have had performance cars before and run premium fuel only (usually recommended for optimum performance). thats why i bought/built the car in the first place.

now i drive a stock 1990 jetta. i also have a stock 1985 gti. they both have 1.8L motors with different compression ratios (and fuel delivery systems) too. jetta first. i filled up with regular. i definatly noticed a difference through the tank. i've switched back to premium now.
gti. i started using premium because i've been sold on the ad that its "cleaning my fuel system as i drive". (its old) it runs way better too now.

i'm a mechanic by trade, and both my cars are in tune and everything functions correctly. i just thought i'd share this simple experience since i'm an enthusiast and a gasoline consumer who drives a "stock" car. premium only for me.

i do get better gas milage with the premium so i figure the $ i save there will offset the higher price i pay at the pump.

[R_Ethug]

Re: Fuel ????

well funny thing is.. my old beater car which was a 91 chysler lebaron v6 obviously i wouldn't run premium in it but i always used to forget about it as I was so used to using it in my old jetta that once in a while i wouldn't pay attention and would fill it with premium..

well the car definetely ran better from the premium but would i choose to always run it in that old beater.. nah..

[RONDAL]

Re: Fuel ????

remember, a LOT of the people who read these forums arent enthusiasts,

you're right....because people that don't care about their cars go onto the internet, joins forums, and post about their cars all the time. The reason we are all on here is because we are car enthusiasts.... otherwise i've made a huge error and obviously stumbled into the wrong forum.

and to khyron; i will dig up the figures from one of the engineers on our team on octane and detonation reduction at altitude. dont quote me but i believe its .5 or 1 full point for every 1000' elevation you gain. i will check and find out for you.

[RedMile04]

Re: Fuel ????

Wow this really did start a good debate! Just on a side note, as I am still looking at picking up an MK4 soon, the 1.8t requires/recommends preium, but just curious if the VR6 does as well?

Thanks now continue with your heated debate!

[forreal]

Re: Fuel ????

Wow this really did start a good debate! Just on a side note, as I am still looking at picking up an MK4 soon, the 1.8t requires/recommends preium, but just curious if the VR6 does as well?

Thanks now continue with your heated debate!

you still havent found a car you like? i remember you from a while back asking me about mine