Gasoline, emissions standards, and driving habits

[Stanley]

Here in CA we're stuck with 91 octane max, reformulated gas, ethanol, all stuff to supposedly reduce emissions. But almost everybody seems to accelerate and drive fast. With low-performance gas you have to stomp harder on the gas to go as fast as you would with better gas. So everybody does. Doesn't that equate to using more gas (and so, more emissions) with the crappy gas?

[siteunseen]

I've always heard that it takes more crappy gas to the same distance. Like generic medication, I take more.

I got censored! Crappy wasn't my first choice but it's similar.

Edited November 22, 2013 by siteunseen

[ajmcforester]

Ethanol is bad I can't find anything good to say about it over gas without it. Get a Ethanol test and find what stations have the least ethanol and water in the gas, and it is simple to use. I did and I drive 6 miles out of my way to avoid ethanol from my home, and I have a gas station on the corner of my street, but they tested as having 5% ethanol.

Octane is not gas performance, more of a knock rating the higher the number the quieter the burn. Now higher compression engines do need higher octane, think about the rating as how hard the gas bangs things in the engine and with higher compression means more force. I had a truck that actually burned less gas and pulled better on the lower octane, but it had relatively low compression. If you have an e-31 head you have higher compression, and if your motor has not been hardened for unleaded fuel you need to add a lead substitute to the gas, this will increase octane and the substitute I use won't burn with an open flame. The other problem with older engines is the amount of required cleaners in the fuel they practically polish the intake valves

What I do is 91 octane with the recommended amount of lead substitute is about 100 Octane not enough octane for a E31 head z car. So I mixed the substitute with an octane booster so when I fill with the mix I get to 115 octane, so that the octane stays higher than it needed while sitting. I'll use this mix before emissions testing about two tanks. Then the rest of the time the mix also has strait weight oil (it must be strait weight oil in 20-30 weight), about .5 oz per ten gallons of fuel. The oil is a protection for rust from any water (especial if I get stuck using ethanol like traveling more that 1/2 tank away) it also keeps the cleaners from over cleaning the valves and other important parts that the lead substitute protects. Also twice a year I'd add one quart to a 1/4 full gas tank drive it hard enough to slosh everything around and coat the whole tank and fill it up this keeps the tank nice and shinny and rust free.

What might start happening when the car is back on the road after restoration is my neighbor does gas testing and could mix me a special batch of gas or a considerate mix to use with pump gas to add, that would be better than what I can get now. I might need to get a small gas tank for the garage to store about 100 gallons of custom gas, and use some smaller bottles for the concentrate mix for road trips.

[Stanley]

I see a bunch of different octane boosters, wonder if they're all the same. I seem to have higher compression with the '81 head I'm running. Should be ok for unleaded but I'm having to set advance to 10 deg at 1000 rpm, supposed to be 17 deg at 700 for the D-606-52, or it pings. I'd really like to see how the car runs when it's set where it's supposed to be. I might mix in some 100 octane race gas for an experiment but gas is too damn expensive as is. No way to do that on a daily basis.

You'd think we'd pay less in CA for the crap gas but no, it's the most expensive in the country, except maybe Hawaii.

Edited November 24, 2013 by Stanley

[SteveJ]

With all of the environmental regs in California, why do you think gas would be cheaper? Did the one Chevron plant ever get back up to capacity after the fire? I doubt there will be a new refinery constructed in California in my lifetime. Plus those gas stations have to pay for the real estate they are sitting on. While they make most of their money off of candy bars & slurpees, the gas sales have to contribute to paying for the overhead.

[djwarner]

Let's not confuse the two issues of Ethanol and Octane. Ethanol actually has an octane rating well over 100. However, ethanol delivers less energy per gallon than gasoline. This is because there is already one oxygen atom in each molecule. This adds weight and volume while eliminating a carbon/hydrogen bond during the burn.

Octane rating does not indicate power available but rather the resistance to detonation (read explode). Modern engines can advance the timing until knock is detected and then back off a tad. This optimizes performance for whatever fuel is used. For our cars with timing that was not dynamically advanced, things are a little problematical. If you set the timing to the book, a particular fuel either knocks or it doesn't. If you set your timing for optimal performance with a certain fuel, you are probably making the best of a suboptimal situation.

If you really want a cheap way to raise octane to get the last bit of timing advance, add 4.5 - 5.0 ounces of acetone to each tank full. This will raise octane about 4 or 5 points for less than a buck. BTW, as been said on this forum many times, the 95 octane rating specified in the owner's manual was calculated in a different way than the way it is done today. Today's 91 octane should do just fine in cars set to factory spec.

As to how much energy is lost with ethanol being added? I used to commute between the west and east coasts of Florida weekly where one coast had little ethanol while the other had almost none. As far as I could figure, ethanol dropped mileage 3-5% or about 1 MPG at highway speeds. This was with a modern, timing adaptive engine.

Edited November 24, 2013 by djwarner

[superj243]

Over the summer on a trip to Panama city beach I put 87 octane in my tank. When i got to the beach my tank was almost completely empty. Recently I took the same trip but filled my car with 93 octane and arrived at the beach with 1/4 of a tank left.

[SteveJ]

And what's your point?

[siteunseen]

I believe he was better at saying what I tried to say, the better the gas the more efficient the motor runs. I'm sure that's common sense but I'm just figuring it out.

[SteveJ]

I believe he was better at saying what I tried to say, the better the gas the more efficient the motor runs. I'm sure that's common sense but I'm just figuring it out.

Actually, he said nothing about the quality of gas. He mentioned different octane ratings. There are some cars out there that will have better performance with higher octane fuels. They generally have knock sensors to signal the ECU to retard timing when lower octane fuel is used.

The owners manual has the recommended octane rating for our cars. Using a higher octane fuel will not change the cars performance, unless you are paying for gas in nickels. In that case, you'll be carrying around fewer nickels after buying the higher octane fuel.

There are a LOT of variables that can affect the performance & (perceived) gas mileage: mixture, tire pressure, winds, traffic, traffic lights, driving style, how full the tank is, etc.

[Stanley]

What about emissions? I know that if the ignition is retarded too much, performance suffers. To go as fast you need to be more heavy-footed. So it seems to me that if you can't get the pump gas that allows timing set where it should be, emissions also will be worse.

Don't know for sure but it sounds right. If so, then there's an environmental reason for having higher octane gas available, right?

[SteveJ]

There isn't an environmental reason for having higher octane gas available. Higher octane gas is used to allow cars to have engines with higher compression with less chance of detonation.

To very much oversimplify emissions:

NOx - This is more of a function of temperature. If your mixture is too lean, it will increase combustion temperatures.

CO - This is more a function of mixture. If the mixture is too rich, there is not enough oxygen to form carbon dioxide. The smog pump on early Z cars basically pumped extra air into the exhaust to allow combustion to complete.

Hydrocarbons - This is a function of mixture and timing. If the timing is too advanced or retarded, you do not give the engine the chance burn the fuel properly.

Note: in the descriptions of the three main emissions components, I did not mention octane.

When you have the engine too far advanced for the octane rating of the fuel, you increase the chance for detonation because the fuel will tend to burn faster in the cylinder, increasing the chance that the combustion gasses have expanded a lot more as the piston is still rising. Hell, if your compression ratio is high enough, you can ignite the mixture without have a spark plug (research a diesel engine).

By the way, tetraethyl lead is a great additive to raise octane levels. I wouldn't consider it environmentally friendly though.