What kinda gasoline you take?

[StormTROOPER]

Because of the rise in gas prices I checked the owner's manual to see if using the cheapest gas was o.k. and was relieved to see REGULAR 87 printed there.

[Cyrk]

I run super cause of the SC, anyone every run mid grade with the SC?

[zko]

Thanks, everyone! _Z

[RitchieDon]

Burn the best gas you can buy!! Low octane gas is for chain saws and lawnmowers. If you can't afford the extra $2.00 per tank, you should have bought a VW instead of a VX. The knock you get on low octane it trying to tell you something - duh.

[VX crazy]

SCed VXs should be running a MINUMUM of 91 octane - run lower and step into it a lot and the computer cannot compensate for it and will soon destroy the engine through probable piston burn through. We do have knock sensors but there can still be some rattle and damage if continued too long. The U.S. uses the following formula: Road Octane Number = (RON + MON)/2. It is a common practice in many European countries to advertise the Research Octane Number on their pumps, so you may see unexpectedly high octane values when travelling abroad.

Unless SCed, use the 87 Octane the owners manual recommends. One - and a very important - exception is that when a vehicle gets older, the normal build-up of fuel- and lubricant-related deposits in the engine can increase the fuel octane number a car requires to prevent engine knock. For this reason, if a car more than a couple of years old experiences engine knocking, the problem may be solved simply by moving to the gasoline with the next-higher anti-knock index.


Following is a great article on selecting the best gasoline for your needs

By: Phil Coconis/autoMedia.com
Many people pick a gas station based on price and/or convenience, probably because they feel that most brands of fuel are pretty much alike. Is that really the case, though? Since your choice of gasoline directly affects engine performance, economy and longevity, along with the environment, it pays to know the facts about different types of fuel.

RON, MON
Let's start with some basic information about octane rating. The term octane is a familiar one and it's important to follow the recommendation that your vehicle's manufacturer specifies in the owner's manual. That number is actually an average of two different octane numbers (Motor Octane, or MON, and Research Octane, RON). These refer to the fuel's ability to resist "knock" (fuel igniting before the ignition spark and resulting in a "flame front") under different driving conditions. MON affects knock at high engine speeds or loads, RON at low ones.
What do these two types of octane measurements have to do with fuel selection? Well, if your engine knocks or pings under only one of these conditions, changing to a different brand of fuel may solve the problem. But if knock occurs under both conditions, then there's likely a mechanical problem that needs attention. It should not be necessary to use a fuel of a higher octane rating, unless all other remedies have been tried.

[b[]Fuel Myths[/b]
We should address a common myth about octane. Know that using fuel of an octane rating higher than that of the manufacturer's recommendation will not increase performance, fuel economy, lower exhaust emissions or increase engine/fuel system life. Usually, only vehicles with high performance engines (fitted with multi-valve heads and/or a supercharger) require a higher-octane fuel.
Does this fact about octane mean that "gasoline is gasoline" and they're all made according to the same formula? Should you just go for the bargain du jour and pocket the difference? Actually, oil companies are competing with each other, and that means that they don't share formulas with each other, nor do they necessarily get their crude oil from the same place. That means the final product will vary, from brand to brand and grade to grade. (And there's even some slight variation within brands, as gas is reformulated both seasonally and geographically, but that's another story.) You do truly get what you pay for—but is it worth it to you?

Price & Grade
Let's examine some of the differences in price and grade. The first is in the quality of the crude oil used. Cheaper grades have more undesirable compounds, such as sulfur, olefins, and diolefins, which cost the refiner to remove. The more of them removed, the higher the price. Since these compounds contribute to higher exhaust emissions, reduced service life of catalytic converters and sludge/varnish buildup in fuel delivery/intake systems, those who plan to keep their vehicles for many years would wisely opt for the better quality gasoline. One easy tip-off that marginal-quality gasoline is being used is a foul sulfur smell emanating from your exhaust (assuming there's no engine malfunction).
Besides having more of the aforementioned compounds removed from them, higher quality fuel also includes more energy enhancing and fuel system cleaning (detergent) additives. These can yield better fuel economy and performance, plus result in reduced maintenance costs. Reformulated Gasoline (RFG), sold in many states and in most urban areas, has also added to the cost and complexity of modern gasoline refining. Although refined under tight government guidelines, there are a variety of formulas, with varying results in terms of cost and performance, with the better performing formulas generally costing more. RFG, deemed necessary to reduce exhaust emissions, differs from earlier gasoline formulas by having more aromatics removed, such as benzene, sulfur, and olefins, as well as the addition of compounds called oxygenates (which raise the oxygen content in gasoline, thereby reducing CO emissions). There are two popular oxygenates used presently—MTBE and Ethanol.

Oxygenates
MTBE (methyl tertiary butyl ether), produced as a result of reacting methanol with isobutylene, is the more stable (less volatile, or prone to evaporation) of the two, and yields a greater octane increase. It tends to produce fewer driveability complaints, and is friendlier to older-car fuel systems. It can be blended, under present rules, at up to 15 percent concentration levels. It is also the more controversial of the two, as it has a higher level of toxicity (not necessarily more toxic than the gasoline it's blended with, though).
Ethanol is produced from fermented grain or corn. Yep, distilled from mash! It's not any more toxic than hard liquor and can be blended at up to 10 percent concentration levels. In Brazil, many vehicles with some modifications to fuel delivery systems run exclusively on the stuff! For environmental reasons, this is the more politically correct of the two oxygenates.
On more modern vehicles with electronic fuel injection, RFG poses no real problem (except for a slight drop in fuel economy), but owners of vehicles with carburetor engines may notice driveability problems under some conditions, due to the effectively "leaner" working fuel mixture. Carburetor modifications, if done skillfully, can solve this problem.
So what's the bottom line? Don't pay extra for a higher octane, unless your owner's manual specifies it or you've modified your engine for higher horsepower. When it comes to choosing between brands of gasoline, however, you may find that paying a bit more at the pump has a definite impact on performance.

© Copyright 2004 autoMedia.com Inc. All Rights Reserved.

[RitchieDon]

After my reply to this post I recieved this message from VX crazy and a -3 rating on my reputation: "VX was designed for low octane and has knock sensors - unless running a blower or higher compression, hi octane is a WASTE and serves NO PURPOSE". I would like to respond by saying that Isuzu had the foresight that high quality octane fuel may not always be available where we go and put these sensors and capabilities in place to compensate for that. Burning good fuel keeps your plugs clean and gives the engine the fuel it needs to perform properly. If octane wasn't an issue, we could all use water. I don't know how to get the negative points off my reputation but I don't think it was fair. Burn chain saw fuel in your VX if you want to, VX crazy, but I'm putting the good stuff in mine.

[Green Dragon]

Burn the best gas you can buy!! Low octane gas is for chain saws and lawnmowers. If you can't afford the extra $2.00 per tank, you should have bought a VW instead of a VX. The knock you get on low octane it trying to tell you something - duh.

Your certainly entitled to your opinion with which I disagree, but it should be expressed with fact rather then contempt.

As for the neg rating, I for one am not in favor of that particular feature on a otherwise superb site.

[RitchieDon]

Thanks, Green Dragon, for helping me with my temper tantrum. My apologizes to all. My VX runs fine with 91 octane or better and I have the same option to put whatever I want in my tank as all of you do. I'll leave the "facts" to you experts.

[xdfarrx]

I use the best I can put in... in all my bike and car.
The fore mentioned post nails the reasons why....
Most cars can adapt to lower and higher grade fuels, via ECU, so at the end of the day I believe it is subjective... I do 'feel' I get more fuel economy with higher grade-

[Jolly Roger VX'er]

I run super cause of the SC, anyone every run mid grade with the SC?

And you can run 87 octane as the engine will retard timing (and power) accordingly. I cheat and use low octane during the week and 93-100 octane on the weekends.

87 is what the book calls for. Supercharger recommends 91+ but our knock sensor is able to handle the lower octane (with noticeably less power) without damage for those with the SC trying to save money...

I'm pretty sure that the mixing occurs at the pump/station - they only have two tanks in the ground too. It is usually cheaper to mix it yourself - do two transactions, one from the regular and one from the premium.

Hi Cyrk...based on all the above I've been alternating fill-ups from 1/2 tank between premium Amoco 93 and regular 87 during the week for regular driving; and running most/all of it out by the weekend or vacation and filling up with pure premium if I'm off and planning any "fun" driving excursions. So far no ill-effects, but, I keep my foot out of the boost to avoid any issues until I know I got a good fill-up of 93.

[spaceCADETzoom]

Yep, generally speaking, if your engine doesn't knock, 87 is just fine. It's a common myth that higher octane means "better" fuel...My VX fill just fine with 87. I have an RX7 that doesn't take anything under 91 and used to have a 240z with the same cultured tastes. We're really talking about the difference between Dasani or Evian and Arrowhead or Sparklets (or even tap). My rotary sportscar won't drink anything but the expensive stuff...ditto for my old 30 year old classic. THe VX, on the other hand, is a spry young thing that is just fine with the normal stuff. The 7 was designed for it...maybe the engineers thought we wouldn't think its a real sports car unless we spent more on it And, yes, higher octane would actually increase plug buildup.

just my 2 cents. i guess there's room for disagreement. sometiems we feel better doing certain things. i am certainly guilty of this.

I didn't even know we had a rating system...does it do anything? I don't see where I can see a poster's rating. I think you got a response about the octane thing because of the way your initial message came out, ritchiedon. Both the way you said it and what you said contributed to someone chiming in. (i.e. the "duh" thing and a subtle implication others would be dumb to fill up on 87)

I don't know about the neg. rating though...that may have came form anyone. Like i said, i didnt even know we had a rating system...and still dont' know its practical purpose. Don't worry too much about it...just a silly number that I don't think anyone pays attention to.

cheers.

[jimbo]

I usually put regular in my VX but every now and then I've tried premium thinking it was "better", and nothing is too good for my baby.

My VX always seemed like it ran a little better, peppier, when I put a full tank of El-Premo in; but I guess that is just my imagination.

No sense in wasting $$$$$$$ , our gas expenditure is high enough already.

Our other car, a VR4, requires premium, and certainly sucks up the gas, slurp-slurp

[Heraclid]

I was running 89 octane mid-grade all the time until just the last few tanks and was happy with it. However, it sure seems like my VX is actually running a bit better on 87 octane now and I've made no other changes to cause that. Plus the weather is getting warmer which usually seems to take the pep down just a tad, but the VX seems slightly peppier. Not a huge difference mind you, but I think 87 may be better for the non-SC'ed folks. The only difference I really felt with 89 octane was right after fill-up, which had nothing to do with the grade of gas. I think the fact that it has a full tank makes it a little peppier for some reason, but I don't know why. Maybe the fuel pump isn't working as hard then and/or the fuel pressure is increased?

[kpaske]

I've run 87 almost exclusively since I bought my VX new in '99. On the few occassions I've experimented with higher octanes, I didn't notice any better performance and actually experienced a decrease in gas mileage. I have running into knocking a bit, especially as my VX has started to get a bit older (I'm at 90k+ miles), but the brand of gas I buy seems to make a difference, so I try to avoid certain brands (ARCO in particular seems to run pretty poorly).