dbaker

The Mobil & QT stations near me sell the Pure Gas at 89 Oct.I run it in all my outdoor machines.Both Top Tier.

\db2

hcvone

We got 93 all over the place in PA, and my local Sunoco has 100 octane on tap always.

marsheng

Pure gasoline stoic is 14.7-1 your new car is stoic at 14.108 and tries to go there which is perfect for E 10 but rich for pure gas and there is no trimming to lean it out because the ECU wants 14.108 only which is rich for pure gas.The oxygen sensors are not monitored under full power as they are narrowband and incapable of measuring A/F under power enrichment and as sophisticated as the cars are they simply go to a dumb program at full power and they are commanded to optimize for E 10 not pure gas.

LDB

You have to be a bit careful about apples to oranges comparisons with Sunoco’s race gas. Are you quoting R octane or (R+M)/2 octane? All normal gas (including both regular and premium) is quoted as (R+M)/2, and the R number will be about 5 higher. The most common and least expensive Sunoco race gas is APEX, which is 100 R octane, but it is only 95 in the apples to apples (R+M)/2 octane. The grade 260GT is 100 (R+M)/2, but is considerably more expensive than APEX, and both APEX and 260GT have 10% ethanol. The highest octane grade that has neither ethanol nor lead is 260GTX at 98 (R+M)/2, and it’s probably not what you are talking about since its R number is 103, not 100. None of that is meant to be in any way critical of Sunoco race gas. It’s simply to point out that they don’t have some magic way of making cheap, unleaded, ethanol-free, 100 apples to apples octane gas.

LDB

Sorry, but that’s mostly not true. While true that the O2 sensors do not respond quickly enough and are not monitored during a full throttle burst, the fuel trims that have been determined during the immediately preceding cruise phase are applied. You are also using stoic a bit wrong. The goal of the ECM is to run very close to 1:1 stoichiometry at all times on all fuels. Stoichiometry of 1:1 is equivalent to an A/F ratio of about 14.7 on pure gas and 14.1 on E10. The fuel trim is what varies the A/F ratio to keep the stoichiometry near 1:1 for all fuels. When you go to fuel enrichment during full throttle, A/F drops a bit, I can’t quote you the exact amount. But suppose you are running E10 which would have a fuel trim near zero, and the table called for A/F to drop by 0.5 to 13.6. If that same car was running E0, fuel trim would have cause the cruising A/F to be about 14.7, and if you floored it, A/F would again drop by the table’s 0.5, making it 14.2. So you’d get the same and correct degree of fuel enrichment running both E0 and E10.

JoesC5

The C5 and the C6 had the GM installed tune set up for 14.7. They were set up for pure gas, not E10.

For the C7, GM changed the tune for 14.1. They are set up for E10, not pure gas.

It does make a slight difference in performance, depending on how the car is tuned( for 14.7 or 14.1)and what gas you run in that particular car.

LDB

As long as the ECM and O2 sensors are functioning properly with no engine trouble light, I respectfully disagree. It shouldn’t make even the tiniest difference. The only conditions where it should matter are if some malfunction has caused the ECM to go off closed loop control, with trouble light on. Under those circumstances it does revert to the raw table with no fuel trim, so you would be better off with the table that is matched to the fuel you are using. But as long as the trouble light isn't on, then even during the warm up period or full throttle bursts where you do go temporarily off closed loop control, the last cruising fuel trim is applied, so you should be appropriate for whatever fuel you are using. The mistake that people make is that they use stoichiometry and A/F interchangeably, but while related, they are not interchangeable. The ECM on closed loop control always goes to 1:1 stoichiometry, meaning an exact 1 to 1 match of the quantity of oxygen required to combust the fuel. OK, OK, that’s a tiny lie, it’s actually a smidgen on the lean side of perfect 1:1 so that there’s a smidgen of excess O2 in exhaust gas. But the ECM will control to that same smidgen of excess O2 regardless of fuel. If you are on E10, the required A/F ratio to get to 1:1 stoichiometry is about 14.1 air to 1 fuel, while on E0 it is about 14.7 air to 1 fuel. Even then, it’s not a fixed and exact 14.1 or 14.7. Slight fuel density and blending variations will cause the fuel trims and resulting A/F to bounce around a little bit from fill up to fill up even if you stay with only E0 (varying a bit around 14.7) or E10 (varying a bit around 14.1).

Rebel Yell

The one time I ran pure gas in a C6 the extra mpg's and performance wasn't worth the extra dollars the gas cost. Plus, these cars were designed to run ethanol gas. Outside of that one time 93 octane E10 is what I've ran since my first C6. Top Tier of course.

Fredtoo

I have seen similar results in the past with a BMW.
I got better MPG with pure gas, but the same $/Mile result, with either pure gas or the ethanol blend.

speedlink

Why would would you want to put ethanol in your gas if you don't need to. Non-ethanol is always better, and better mileage as well.

N875ED

This week, President Trump announced E15 would become the standard gasoline grade...so we can help the corn farmers. Any thoughts about how our cars will perform on this fuel?

Z06_Ruff

I personally run straight flex fuel in my Vette. It's the new wave. Get on board or get left behind. 🌽 is here to stay.

mschuyler

I just use the highest octane available wherever I am at. It varies by state and season. I never buy on price and I only go to Top Tier stations, usually Shell or Chevron because that's what is around here. I don't track, so there's no reason to worry about any of this other stuff. No worries and running fine.

MikeyTX

Works great in my m/c and the zero turn-mower. It seems to keep the carb much cleaner.

LDB

I don’t have detailed firsthand knowledge about E15, as it was not being seriously considered when I retired. However, certain things are clear, as outlined in this first paragraph. Uncertainties are in the last paragraph. There should not be any problems with the ECM, injectors, engine performance, horsepower, drivability, etc. All of those should perform as in earlier posts, simply adjusting to A/F of about 13.8 instead of the 14.7 for pure gas or 14.1 for E10. That’s well within the adjustment range of cars built since the late 1990’s. Flex fuel capability is not needed. Mileage loss will increase from 2-3% for E10 to 3-5% for E15. Air pollution will increase slightly during the summer because ethanol is high vapor pressure, so a summer vapor pressure waiver will be required, and a bit more unburned fuel will escape to the atmosphere. There’s a bit of irony there for something that’s supposed to be environmentally friendly, but it’s not a problem for the car. And of course the economic insanity for zero benefit to anyone but politicians, farmers, and ethanol plant owners will get worse. But none of the above represents a risk to the car or a threat to reduce the performance (other than gas mileage) of the car.

The uncertainty is the degree, if any, to which E15 is more corrosive than E10, and thus represents an increased risk of failure to things like fuel pumps, fuel lines, gaskets, and other components in direct contact with the fuel. This is where I don’t have firsthand knowledge since my retirement, but my sense is that the risk is fairly low. The reason I say that is that essentially all of the articles warning about that come from sources that made similar dire claims about E10 in years gone by, so their credibility is at least somewhat questionable. Even with the car companies that object, their credibility in resisting change leaves something to be desired. So I guess overall, while I dislike the economic/political stupidity of E15 about 1.5 times as much as E10, I’m not overly concerned that it will be a maintenance disaster.

Rebel Yell

Thank you sir. It's good to hear from someone that is knowledgeable on a subject, and also has some skin skin the game.

Charlie442

E0 fuel IS NOT off road fuel..leaded race gas is..in Wisconsin, fuel that is off road is labeled as such..if you aren t in the 6 ciunty area around Milwaukee, you can buy ethanol free premium all over the state..

Vetteman Jack

Revival of a five year old thread.