Don't buy a 35-40k car and then try to skimp on the gas. My G has seen nothing but Amoco Ultimate.

 

I use chevron's best offering, it is 94 octane. I have also heard that chevron has some of the cleanest gas.

 

I asked the dealer this same question. As I was going to pick up my new g35x on 4/17/07, I see them topping off one at the gas station next door. The kid tells me that it's another new one that is being picked up in a couple hours. I look and see he is putting in the lowest grade gas. I ask him about it and he tells me they always put in the cheap gas. Later at the dealership the sales guys all tell me the same thing, use the cheap stuff, all though it says premium on the gas door and in the manual. Good thing I haven't had to fill up yet and I'll definitely be using the good stuff.

 

Well... Does this question have to be brought up? I mean... c'mon... it's up to you to put GOOD GAS, presumably >90 octane, and BAD GAS, <90 octane gas.... I'm not saying that <90 octane gases are necessarily bad... but as you know, the more octane in the gas, the better gas burns up in the engine. ALSO, if you want to follow the direction more than follow your insticts... you can always refer to the owner's manual by putting premium gas in your gas tank....

What I'm trying to say is that it really is all depending on your "taste" or "preference".

 

This is not necessarily true. Octane rating is a measure of explosion inhibition properties. The higher the octane number, the more the gas is resistant to flash under pressure.

You want a high octane rated gas in a high compression engine. As the fuel is compressed, you don't want it to explode until the point when the spark plug ignites it. If you use low octane fuel, it will possibly explode before the spark, causing detonation (spark knock).

 

This is what I've been told by many "experts", at least that's what they call themselves. I'm just a consumer and don't engineer this stuff. "Buy only as high of a grade as needed to prevent knock. Anything more is not a treat for your car it's just a waste of money". So they say. I was interested the other day when I learned octane rating are nothing more that a number indicating how resistant the fuel is to causing knock. I don't think high octanes are more powerful they are just less volatile. Knock as I understand it is when fuel in your engine explodes due to heat, and not only from the spark from your plugs which is precisely timed. Lower octane explodes at lower temps, high octanes at higher temps. Is there anyone on this site that knows for sure and can link some fuel expert’s opinions? I'd hate to buy lower grade fuel that will cost my money in repair later on, but also hate to waste money on fuel that is unnecessary. I have plenty of other things to do with my cash than give it you Hugo Chavez.



How much octane does your engine really need?

The least amount that's necessary to prevent detonation (spark knock). On most vehicles, that's 87 octane regular grade unleaded gasoline. But on higher compression engines, or turbocharged or supercharged engines, the engine may require premium grade 91 to 93 octane fuels.

Detonation (spark knock) occurs when the octane rating of the fuel isn't high enough to handle the heat and pressure. Detonation is most noticeable when lugging the engine under load or accelerating. It may sound like a pinging, clattering or rattling noise. Instead of a single flame front forming when the fuel is ignited, multiple flame front form spontaneously throughout the combustion chamber. These collide and produce shock waves that cause the noise. The hammer-like blows produced by detonation are very hard on the pistons, head gasket and bearings and may damage the engine if the problem is not corrected.

Other common causes of detonation (besides low octane gasoline) include: a faulty Exhaust Gas Recirculation (EGR) system, too much compression due to a build up of carbon deposits in the combustion chambers (use a top cleaner to clean the combustion chambers), a lean fuel condition (dirty fuel injectors), or engine overheating.

Most late model engines have a "knock" sensor to detect engine vibrations caused by detonation. When the sensor detects detonation, it signals the PCM to temporarily retard spark timing. This helps protect the engine from possible detonation damage, but it also reduces engine performance and fuel economy.

GASOLINE OCTANE

One way to prevent detonation is to use a higher octane fuel. The octane rating of a motor fuel is a measure of its detonation resistance. The octane that's posted on the filling station pump is "pump octane," which is an average of something called "research" and "motor" octane ratings (which are two different laboratory methods of measuring octane). The higher the pump octane number, the better able the fuel is to resist detonation.

A gasoline's octane rating depends on the blend of hydrocarbons in the fuel and other ingredients that are added to it. Tetraethyl lead was long used as an anti-knock additive to improve gasoline octane. In fact, it was the most effective and least expensive octane-boosting additive that could be used for this purpose. But leaded fuel cannot be used in a vehicle with a catalytic converter because the lead fouls the catalyst. So

unleaded fuels use other octane-boosting additives such as MBTE or ethanol alcohol.

Most regular grade gasolines today are rated at 87 octane, which is sufficient for engines with compression ratios of up to about 9 to 1. Higher compression engines, engines with turbochargers or superchargers, or ones used frequently for towing usually require a higher octane rating or a premium grade of gasoline.

CAUTION: Follow the fuel recommendations in your vehicle owner's manual. If your vehicle requires premium 91 or higher octane fuel, use a premium grade of gasoline.

If you can't find pump gas with a high enough octane to prevent detonation, you can always add an aftermarket octane boosting fuel additive to your fuel tank. Such products can boost the octane rating of ordinary pump gas several points depending on the concentration used (always follow directions).

But even this might not be enough to eliminate a persistent spark knock if your engine has an underlying problem.

 

 

I always use premium but my question is does where you buy it at matter?

I have been buying all my gas at Costco do you think that is okay?

 

Thanks for the post, Cash.

I'm really feeling good about that Shell gas card now that it is "Tron Guy" approved...

 

Different companies have different standards. I always try to buy from a top-tier rated company.

Discount fuel stores buy from whoever is cheapest at the time. You might luck out and get Chevron, but you might not and get some gas loaded with sulphur and coke. It's a gamble.

 

gas is gas but where chevron, shell, mobil, etc differ cheaper gas stations is the additives they put in to help treat and clean your fuel system.

 

I use a 95 Octane gas. 98 is also available.

Do I need to switch?

And Will I need to empty the old gas before switching to the higher octane one?

VidER

 

beathorse

 

Are you serious?? No, you don't need to switch.

 

Yes I am serious.

95 is actually the lowest you can get here!

VidER