Question on Octane

[PHXGT]

I live in Az where the premium fuels are 91 octane. There are a few stations that sell 93 and/or 100. Will our car's "brain" automatically adjust mapping and timing if a higher octane is put in the tank? Or, do you need a special tune for ratings as high as 100. Sorry if this is a stupid question. I just don't know much about this stuff.

 

[BlackICE]

I live in Az where the premium fuels are 91 octane. There are a few stations that sell 93 and/or 100. Will our car's "brain" automatically adjust mapping and timing if a higher octane is put in the tank? Or, do you need a special tune for ratings as high as 100. Sorry if this is a stupid question. I just don't know much about this stuff.

Unfortunately our GTs don't have a knock sensor, so they cannot tell what octane gas you are running. Therefore the cars are mapped to run on 91 octane gas the lowest octane premium in the US. Putting in higher octane gas will give you nothing without a retune of the ECM to take advantage of it.

 

[MAD IN NC]

Beyond the retune to 93 - more and more stations are using ethanol blends. Manual says no ethaonol though but many of us just don't have the choice going forward in time.

Does anybody knows what the impact of ethanol will have on a tune 93 program, pulley, whipple etc...

 

[BlackICE]

Beyond the retune to 93 - more and more stations are using ethanol blends. Manual says no ethaonol though but many of us just don't have the choice going forward in time.

Does anybody knows what the impact of ethanol will have on a tune 93 program, pulley, whipple etc...

In CA it think all of the gas has ethanol, since they got rid of MTBE.

Disclaimer, this is me making a guess based on theory not practice, so if you have better information please correct mine. No flames please.

Ethanol has only about 60% of the energy of gasoline by volume and a Stoichiometric air-fuel ratio of 9 vs. 14 for gasoline. This shouldn't be a problem when operating closed loop e.i. part throttle. At WOT and open loop operation a 10% ethanol mix would be running leaner than pure gasoline. Assuming the engine was set to 12:1 then with 10% ethanol it would really be running lean and should be set at 11.7:1 when running gasoline to get the right a/f with the ethanol.

Note that ethanol as a higher octane rating than gasoline so the a/f ratio can be a little leaner anyway. If you optimize a tune for a ethanol blend you will get more power the higher % of ethanol you use. The limiting factor would be the fuel system ability to inject the higher volume of fuel needed and the corrosiveness of ethanol on the engine and fuel system.

Ethanol info:

http://www.ext.colostate.edu/Pubs/farmmgt/05010.html

 

[barondw]

Agree with BlackIce. Also the amount of etrhanol I am sure is varied depending upon the gasoline company's marketing/profit plan.

It is very noticeable when checking mileage as to the negative impact of ethanol.

Dave

 

[BlackICE]

Ethanol use in gasoline is a complete farce, it does nothing for the environment, it cost more, you get less mpg. That said, I think the lobbyist are too strong and our elected official to dumb, or greedy to stop the ethanol.

US production cost are about $1.60 a gallon for ethanol, given its lower energy density it is equivalent to only .60 gallons of gasoline. That means the production cost is really about $2.66 for a gallon equivalent of gasoline.

This is way higher than the production cost of gasoline!

Not to fear, goveronment subsidies and higher prices at the pump wil make up the difference. Oil companies will just charge you more while you get less energy per gallon.

So I bought more ADM stock during the last stock mkt drop.

 

[barondw]

Prefer BG over ADM.

Dave

 

[B O N Y]

Ethanol is a rip off of the consumer. I bought Pacific Ethanol, sold it, made a few schekels. The Chairman is Bill Jones, former Secretary Of State of California. Great for the subsidized companies, horrible for your car.

 

[50 BMG]

There are a few stations that sell 93 and/or 100.

A station in PHX is selling 93 at the pump...

WHERE?

 

[Fast Freddy]

A station in PHX is selling 93 at the pump...

WHERE?

this is not true. 93 is not available anywhere in the state. some pumps sell 100 octane unleaded race gas though. there are 2 gas stations that sell it at the pump here in tucson.

 

[PHXGT]

I am probably wrong on the 93 octane. I was told that the Union 76 station at the Scottsdale Promenade (Indian Bend and Pima) sold 93 or 95 octane. I have not seen it and trust Fast Freddy is right.

 

[AZGT]

You can buy race gas (100 octane?) at the station at the corner of 56th and Bell.

 

[analogdesigner]

MTBE and ethanol are both HUGE SCAMS!:thumbsdow :bs

Thank the "Al Gore types" for this one. I think that many persons have good intentions, however, they lack the scientific knowledge to truly understand the "well-to-wheel" efficiency of these poor fuel alternatives.

 

[cobrar1339]

Since the ethanol craze Corn is at an all time high.

This means poulty and Beef will go up in price as they are feed with corn. The big farmers think this is wrong as well, but the govt is kicking in for product of corn and ethanol.

What good is this stuff if the world goes hungry. Who would want to plant anything else with all the kick backs.

As stated it does not do much for the environment.

I say drill :thumbsup

 

[Black2003Cobra]

Around here, we have 10% ethanol (by volume) in our pump gas. That reduces stoich (AFRs) from around 14.6 down to just about 14.0. As mentioned, in closed loop, since the O2 sensors are reading lambda, this really isn’t a problem. But for a typical boosted application, to maintain an equivalence ratio (φ = 1/λ = AFRs/AFR) of say around 1.25 at WOT, that means one should be running an AFR of ~11.2 (vs ~11.7 for straight gasoline.)

Ethanol does have a higher latent heat of vaporization than gasoline, which is advantageous. It also has a higher RON (& MON up to about 15% by volume) than gasoline. On the other hand, as mentioned, it has a lower energy density. And even though stoich is lower, those two effects just about cancel. And since you have to run more of it with its lower stoich, that means fuel economy sucketh!

Here's a graph of AFRs vs % ethanol (and meth), by volume.

 

[californiacuda]

With more fuel used and lower mpg comes lower temps, and the ability to run more boost.

 

[Black2003Cobra]

With more fuel used and lower mpg comes lower temps, and the ability to run more boost.

Yes. There is some additional cooling effect. (That’s where having a higher latent heat of vaporization comes in. The extra mass of fuel helps, too, but that isn’t nearly as large an effect.) Yet at only 10% ethanol by volume, the overall effect isn’t very big. If one works it all out, (for the conditions I mentioned above), they’ll see that the decrease in charge temps is only about 6°C. So not that it doesn’t go in the right direction, but personally I wouldn’t want to increase boost any with that small of a change if you follow me.

 

[californiacuda]

I was primarily thinking of the benefit of e85.

 

[Black2003Cobra]

Ah, I see. For that case, yes, the effect is more significant, of course! In fact, that is exactly what Saab does with their FFV turbo. When running on E85, the boost pressure is raised, hence the added power. And of course the higher the percent ethanol, the lower AFRs gets, and the higher the BSFC gets! So you need a bigger fuel tank. There’s also a cold start problem. (The tradeoff of the higher Lvap). That’s why it is typical to switch the blend from 85/15 in the summer to 70/30 in the winter. Then there’s the hard-core, blown-alcohol guys that run straight methanol (which has an even higher Lvap) with CR’s of over 17:1, boost pressures above 50 psi, and boat loads of timing! Obviously they could care less about fuel economy! They also have to clean out their fuel system after every event.

But I digress! Sorry for getting so off track!