our JDM evo's are tuned for 98+ and our pump here is like 90 :-(

 

I never really thought about it, but I have found a difference. I religiously filled up with Mobil gas. Then out of desperation I filled up at a Kroger (uses shell) and my car seems to run much better. Might be placebo, but it certainly seems smoother and upon doing a pull, I am not getting the 1s and 2s of knock I was getting with the Mobil gas.

 

i feel all gas stations are roughly the same, however, the "discount gas" stations like ARCO and KANGAROO, or watever, are crappy. For my own enjoyment i ran my car bone dry, put 4 gallons of Kangaroo in, and what do u know, 3-6 counts of consistant knock in all gears at WOT. I've logged my car with alot of different gas stations and they all were fine, except the discount ones..

 

very interesting im going to try bp or mobile i do get alot of 1 and 2 counts of knock with this gas. just weather is so inconsistent here this time of yr its hard to say the knock is gas related vs heat and humidity related.

 

I agree, stick to name brands and you should be fine. I know Buschur had a lot of issues tuning cars running valero which isn't popular around here but i avoid the few stations they have. I have logged/tuned almost every type of local gas: shell, Hess, gulf, mobil, sunoco, Irving, BP. All work great, none seem to cause more knock on a decently agressive tune. That said, i tend to fill up with the cheapest gas, tends to be Gulf or Hess.

 

i seem to have a smoother idle with some brands of gas vs. others

 

As a oil and gas engineer I can tell you that almost all stations in a particular area will use the same base stock. This means the gas is normally refined at the same refinery, transported via the same pipeline to the same storage tanks, and then transported in the same bulk transport 18 wheelers to different stations.

This is why you will often see the same Transport company's trucks filling different station's underground tanks. Very rarely will you have 2 or more distribution companies having the same geographical territory, but even in that case the gas still normally comes from the same refinery and pipeline. FWIW, there are about 14 or so different gasoline formulations based on where you are in the country and what time of year it is. This is very costly for the oil companies to change formulations and segregate their distribution to comply with asinine laws across various states (CA being the biggest pain).

The only difference is the additive packages that each brand adds to the base stock. This can, and often does vary greatly in concentration and chemicals used. The largest percentage of an additive will be normally MTBE, ETBE or ethanol, and then added to that will be a very small percentage (by volume) of the particular brands additive. Unfortunately, the exact chemical compositions of the mfr's additives are not normally disclosed. Most of them will normally contain detergents (Deposit Control Additives), oxygenates, corrosion inhibitor and a dye at a minimum. Some may even add additional aromatics for anti-knock, but again, it depends on the additive blend.

The best way to test this would be to become friends with the operations manager at the distribution company's depot, then ask him if he could provide samples of the base stock and some mixed samples for the different brand additives. Then you would need to obtain a SAE test motor for the Motor and Research Octane tests, use a scientific test method with at least 3 averages, and see if the octane numbers are noticeably different. Then you would have an answer as to which package of additives produces the highest AKI. Then, to take advantage of that, you would then advance your timing to take full advantage of the extra octane.

But all this leaves out one very important variable, underground storage tanks; which is a whole different animal. So, as a rule of thumb, I recommend choosing stations with the newest underground tanks. How do you tell that? No real easy way to do that, unfortunately. Easiest way is to drive around town and look for a huge excavation project and some big tanks going in the ground, followed by a gas station opening a couple months later. Those would be the newest, so use those. Short of that, or running into an owner or manager who knows when the tanks were installed, you can use the ol scientific guess method. Look for freshly poured concrete, newer fill covers and vent ports, lack of patches in the concrete or asphalt and other general "new vs. old" signs. Trust me, I've seen the bottom of 1 million gal storage containers, and done numerous chemical cleaning on the pipelines that transport them. Believe me when I tell you that old tanks and pipelines can build up an awful lot of sediments, precipitants and debris over the years.

So to answer a short question with a really long answer, pick a newly constructed gas station with fresh underground tanks, base your tune off that gas, and be a little cautious when you travel elsewhere and get gas from other stations.

 

^^^ This guy knows what he is talking about.

 

dude (oil and gas engineer above): do you do your own tuning? Which brand of fuel to you run?

 

I used to, but haven't kept up all that well with all the recent developments since I've been working so much lately. I finally got around to installing a whole bunch of mods I've had sitting in the garage and am having Jay from boosted tuning help me out.

But to answer your question, I normally try to stick to top tier certified gasolines. My preference is as Follows;

1. ConocoPhillips Gas (Conoco, Phillips 66, Unocal 76)
2. Chevron
3. Shell
4. ExxonMobil (Exxon, Mobil, or Esso)

Between these 4 choices I've not been anywhere in the country that I couldn't find one of the above stations. But keep in mind what I said about how new the underground tanks are. Tough to do while travelling, I must admit. I'm most partial to ConocoPhillips, Chevron and ExxonMobil since they have employed me and Royal Dutch Shell has not. Only problem is that Shell stations are much more prevalent out here than ExxonMobil, hence they get bumped up in the ranking.

 

I don't have any Evo specific info, but in my POS ford contour, I did notice that BP's 87 octane was a lot "snappier" though I went through the tank about 20 miles sooner. Keep in mind,though, that a noticeable difference in power in that car would be 5 HP or so.