c6miller

When I'm in North Carolina there are several stations that have 93 pure gas that I use in my 2012 GS, but they are non-branded names. I was told by one station manager they have no additives or detergents in their 100% gas. If that's correct, do you add techron or is it just better to use a top tier name. The pure gas is about 3.12/gl and Chevron/Exxon 2.89. I seen to get 2-3 miles more a gallon on the ethanol free.

Kent1999

OH boy... here we go.

Cue the anti-ethanol jihadists!

Without choosing sides --

1) Detergents and additives are a good thing for gasoline. If going with the "100%" gas, I'd add some Techron.

2) More octane isn't *necessarily* better. If your 2012 GS is stock, I doubt you'll see any measurable performance improvement from using a 93 octane fuel vs. a 91, but I don't know this for a fact. I'd ask some of the tuners chime in here, and tell us how much spark retard a fully stock LS3 engine typically sees on 91 pump gas due to knock/detonation.

dryadsdad

We do have a resident expert and IIRC, he said all petrol sold in the US has detergents and additives. It must or it's not auto fuel.

I think you were told wrong. Yes, I'd add techron. Note, lack of ethanol will only get you some slight increase in MPG. You will have to watch carefully to see it, tho.

Rebel Yell

Personally after using the pure gas, I can't see enough boost in mileage to account for the higher cost. These engines are designed to run on ethanol, and I do like that with the top tier gas the cleaners do help the engine. It is a matter of preference though.

Bruze

on all points.

Don-Vette

Your engine is designed to run ethanol gas. Top Tier isn't recommended in your owner's manual for nothing, the detergents keep your valves clean. Why run non ethanol only to have to add an additive? Makes no sense IMO.Top tier 93 for me.

Zero_6

If gas has additivi then why does gas pumps have those "may contain ethano" logos/sticker?

Bruze

I'm pretty sure ALL gas has additives of one sort or another.

But ethanol isn't really considered an additive like the others, so the pumps are just telling you if it does or does not have ethanol.

ls1121

When I lived in Roanoke VA. I used to run Pure Gas because it was around the same price and my Camaro really liked it i put it in my Vette also but not every fill up and I use techron regardless. I now live in Charlotte NC and I get Top Tier QT gas Premium for $2.23. I cannot find Pure Gas for no where close to that price or I would still be using it. Ethanol is just a fancy word for Moonshine with poison added so we humans cannot drink it lol. I know a corn farmer in Ohio who sells to ethanol plants.

Ben101er

I can't say for sure, but I know that there are many small engines, such as older lawn tractors and generators, that cannot use ethanol. It eats up the rubber diaphragms in the carbs. Older vehicles don't run great on ethanol, either. My guess is they are just playing cya.

jrose7004

I use 100% gas in my car and I run a bottle of Techron through it every 5th tankful or so.

LDB

I’ve said this before in any number of posts and threads: from the standpoint of performance in your car, top tier with ethanol is the clear and obvious winner. I say that with the dual credibility that I’m a retired refining engineer who has seen actual engine testing data, and also, I dislike ethanol in gas. But the reason for my dislike is that it costs too much and does not deliver the alleged environmental benefits. As far as performance, most of the horror stories are internet balderdash. True, gas mileage will be about 3-5% less with ethanol. Also true, if you store your car over the winter, there is slightly more risk related to water separation, but that can be eliminated with stabilizer. And finally, also true that with pre-1990 cars and small equipment like chain saws and weed eaters, there are certain added risks. But for a reasonably current car that is not in long term storage, the one and only performance disadvantage is the 3-5% mileage penalty.

As far as additives, differences over a few thousand miles are essentially zilch. All gas has a minimum, EPA-mandated additive package that will keep your engine reasonably clean. But if you tear down an engine that has run 50,000 miles on top tier and compare it to one that has run on non-top-tier, the difference will be obvious even to the eyeball. The top tier engine will have cleaner valves, injectors, spark plugs, and piston crowns. That doesn’t mean the non-top-tier engine will be in terrible shape, it just means the top tier engine will clearly be cleaner. As far as the strategy of using non-top-tier with an occasional can of Techron or similar additive, while that will be better than non-top-tier alone, think of it this way. Suppose the way you washed your clothes was that 4 times out of 5, you only used half the recommended dose of soap, and then the fifth time, you used a triple dose of soap. Do you suppose your clothes would be as clean as they would be if you consistently used the proper dose of soap?

SladeX

On my trip to Bowling Green then Myrtle Beach, I had pure-gas.org bookmarked. In at least 1 segment of my trip I had to use ethanol gas. That segment had the worst gas mileage. The majority of the trip with non-ethanol gas, I had 31mpg avg and on nice flat sections @ 75mph I was hitting 32 a few times. ethanol would hover in the 29-30 range.

I would use 94 ethanol for track use on my LS3 cammed/headers camaro and non ethanol for the drive there and home. That car shows a lot more sensitivity in gas mileage for ethanol/non ethanol.

Mike's LS3

Nice to read an interesting, informative post that answers the OP's question.

With the added ethanol (10%) in our fuel, today's auto manufacturers are tuning cars with a lower stoich (A/F ratio at cruise) value of around 14.13 compared to 14.7 for 100% gas. Has that closed the fuel economy gap between 10% ethanol vs 100% gas?

LDB

You have to be a bit careful with terms. If you say stoichiometric air to fuel ratio, you mean that exactly the right amount of air and fuel are being mixed so that you are neither too rich nor too lean. If you have pure gas with no ethanol, the air to fuel ratio required to be stoichiometric is about 14.7 to 1, while with 10% ethanol, it drops to about 14.2 to 1. But those ratios are not stoichiometric ratios, they are air to fuel ratios required to give 1 to 1 stoichiometry. In both cases, the stoichiometric ratio is 1 to 1, meaning that exactly the right abount of air and fuel are being mixed so that you have neither too much nor too little oxygen.

In terms of the engine tuning, cars are not tuned to a specific air to fuel ratio, they are tuned to a very low, but not quite zero amount of excess O2 in the exhaust gas. So let’s suppose that your car has been running on pure gas and you fill up with ethanol gas. Immediately after you start your car, the engine computer will remember the settings from before the fill up, and it will be running too high an air to fuel ratio. The O2 sensor will then sense that there is too much excess O2 in the exhaust, and it will very quickly reset the engine computer to a lower air to fuel ratio to bring the excess O2 reading back to normal. So in essence, ever since cars started using exhaust O2 sensors in the early 1990’s, air to fuel ratio is not a design parameter. Excess O2 in the exhaust is the design parameter, and the computer sets air to fuel ratio to whatever is needed to achieve that O2 in the exhaust target.

So coming back to Mike’s question, no, the fuel economy gap has not been reduced by any recent changes in air to fuel because there haven’t been any recent changes. What causes the reduced mileage with ethanol is that it contains less energy per gallon than gas does. So less energy per gallon means less miles per gallon. But don’t take that logic too far. It does not mean less power. The engine computer’s adjustment of air to fuel as outlined earlier means that under any given conditions, more fuel is being injected with ethanol, so while mileage drops due to more fuel being injected, power stays the same.

psp6158

I read an interesting thread by him where he says to use a certain fuel for 5000 miles and change brands as the new fuel will wash away deposits from the last fuel, but will leave its own, repeat

LDB

If you mean me agreeing with the theory that rotating among top tier brands is a good idea to get several different “flavors” of detergent, you may have misinterpreted what I said. It is true that if you go back several decades, to the 1960’s and 1970’s as great leaps in gasoline detergents were being made, that idea made a lot of sense. One brand’s detergent package might do the best job at keeping valves clean, another best at injectors, another best at plugs, etc. But as detergent packages have matured, the top tier detergent packages have all become very good at keeping all areas clean. So the logic to rotate among top tier brands is much weaker than it used to be. Today, I’d say that while it can’t hurt, it isn’t likely to do much good either. Once you are using a top tier brand, you will be very clean. Debating which one is the very cleanest among the very clean, or trying to squeeze out a bit more by rotating among brands, is not likely to generate big differences. To whatever small extent there are differences, it will be in “catch up”, not in “steady state”. That means that one may still be a bit better than another in cleaning up a dirty engine that has run for a long time on cheapo gas, but if you start out using top tier and stay with it, they will all be so clean that differences won’t be enough to worry about.

dryadsdad

I'm curious, LDB, you say a tear down will show by eyeball which engine ran on top tier and which didn't. Does it make any functional difference? That is, will a bit of a buildup on piston crowns or valves away from the seats affect engine performance in a meaningful way?

LDB

I do not have hard, scientific data to say how much difference it makes, but two things suggest it isn’t trivial. First, the car companies obviously think it will reduce their warranty claims enough to have developed the top tier specs in the first place and to continue to sponsor it (remember, it is a car company program, not an oil company program). Second, your intuition will tell you that while the exact amount of difference to performance and maintenance isn’t obvious, it would be virtually impossible to argue that improved cleanliness doesn’t directionally help. But if you are looking for hard, scientific data that says using top tier will improve performance by X% or reduce maintenance cost by Y%, no, we never tried to generate that kind of data. I presume that car companies probably have that kind of data, which they used in justifying top tier. But that would not be the kind of information that they share.

Sunset-C6

Buy the cheapest gas money can buy.....