the book says to use 91 octane and 87 at a minimum. so does it matter which one i use?

 

The higher the octane, the hotter it burns, the better it is for the engine. It keeps it clean too I'm sure, reducing carbon buildup.

 

octane only means its burn rate not how hot it makes a engine ( false info) as of 1975 ALL cars are made to run on regular , high test is a waste of money and high octane burns cooler not hotter .so if you have LOTS OF MONEY burn aircraft gas 114+ octane if not use regular . $3.77 vs $4.11 i think the choice should be clear and for the differance in price the very little if any extra mileage occur's its not worth it

 

I use 105 octane, because I can and because the engine/ECU compensates for it.
You are wrong about all cars being made to run on regular. They will run but you risk engine damage on some engines. Certain Jaguars and turbocharged Volvos immediately come to mind.
Higher octane fuel, on engines developed to run it, will most certainly produce more power and get better economy on higher octane fuels than lower octane fuels. I know because I've done it.
On engines with a knock sensor, the ECU will retard timing when it senses knock, which it will all the time if using low grade fuels. This kills power and economy.
Higher octane fuel burns neither hotter nor colder, it has a higher resistance to ignition, which is helpful in engines that have higher compression or are turbocharged, it helps prevent pre ignition or detonation. These engines are tuned by way of spark advance, to get the most out of the higher octane fuel.

 

I use 93 and get 15% better mpg.

 

Man o' man... It surly has to do with compression ratios. My 94 NA has a comp ratio of 10.5/1 and the owners man says Premium is recommend. The turbo has a ratio of 8.5/1 I Was wondering what the book says, regarding or premium? Higher compression usually equates to higher octain as far as I know. (Except in the newist VVT engines ).

 

To answer the op's question, it doesn't matter in this case. Yes, it mattered on my 2000 Miata; it pinged badly on 87 and needed 91, but my '97 850 glt can run on either. Better perf and mileage on 91 but runs fine on 87, too. Typhoon hit it on the head

 

+1

BTW, I use 92 on both my tuned Volvo's.

 

So you have had no issues running E85? I was interested in tossing a couple gallons in to see if this car will hold up, I know its great for the turbo. I ran it in previous cars with mixed results.

 

No issues at all. Its into winter here, cold starts are a bit more difficult than on 98 unleaded, but nothing to cry about.
The fuel system is holding up fine.
If you are going to go E85, you have to commit to it. I have 440cc injectors and ECU chips (although you don't NEED ECU chips, it helps a lot to extract more performance).
My fuel consumption has dropped maybe 10% at worst commuting and the car has a lot more usable torque everywhere in the rev range. The turbo loves it.
The car will also still run just fine on 98 with the larger injectors, it just hurts fuel economy a little. Bosch EFI adapts very well to this fuel.

 

Wow... a lot of bad information on here about octane. Higher octane fuel burns slower. That's it. It allows an engine to run higher compression or forced induction, because lower octane fuel will ignite before it's supposed to, which is known as preignition or "spark knock/ pinging,", which can damage an engine. Now, our cars CAN use regular, but the computer will retard the ignition- this is what the knock sensors are for- in order to counteract the preignition. This will reduce performance and economy. Other cars don't have such a setup, or have such high compression/ high pressure turbo/ superchargers that low octane fuel will actually ignite from the heat of compression alone, and so REQUIRE high octane fuel, or else the engine will be damaged. You can safely run regular in these cars- the computer will adjust. However, you'll lose power and economy, and it negates any financial gain from saving the extra money.

As for E85, ethanol is a high octane fuel. It allows significantly higher boost, and can be used as part of a package to improve performance. However, without supporting mods, you WILL damage the car. Ethanol will eat away at rubber components in the fuel system. Also, it has a lower energy density than gasoline, so you run the risk of the car running lean, which can damage the engine- hence the need for larger injectors. Fuel consumption will go up, too. Just adding E85 to a stock car is asking for trouble.

 

You need to talk to people who actually run E85 and ignore the ignorant internet ramblings on ethanol.

 

My volvos never liked Northeastern regular -- they are primadonnas -- just premium...

 

Google octane; here's some pretty good info from here:

Higher octane ratings correlate to higher activation energies: This being the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition or detonation.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels ignite less easily. However, detonation is undesirable in a spark ignition engine, and is signified by audible "pinking" or in more extreme cases "knock".
A fuel with a higher octane rating can be burnt in an engine with a high compression ratio without causing detonation, as such fuels are less prone to detonation. Compression is directly related to power and to thermodynamic efficiency (see engine tuning), so engines that require a higher octane fuel usually develop more motive power and therefore do more work in relation to the calorific value of the fuel (BTU) being used. Power output is a function of the properties of the fuel used, as well as the design of the engine itself, and is related to octane rating of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be brought into the combustion chamber. When the throttle is partly open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below that of the external atmosphere (depression). In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to almost that of the external atmosphere, or higher in the case of forced induction engines (See supercharged or turbocharged engines).
Many high-performance engines are designed to operate with a high maximum compression, and thus demand fuels of higher octane. A common misconception is that power output or fuel efficiency can be improved by burning fuel of higher octane than that specified by the engine manufacturer. The power output of an engine depends in part on the energy density of the fuel being burnt. Fuels of different octane ratings may have similar densities, but because switching to a higher octane fuel does not add more hydrocarbon content or oxygen, the engine cannot develop more power.
However, burning fuel with a lower octane rating than that for which the engine is designed often results in a reduction of power output and efficiency. Many modern engines are equipped with a knock sensor (a small piezoelectric microphone), which sends a signal to the engine control unit, which in turn retards the ignition timing when detonation is detected. Retarding the ignition timing reduces the tendency of the fuel-air mixture to detonate, but also reduces power output and fuel efficiency. Because of this, under conditions of high load and high temperature, a given engine may have a more consistent power output with a higher octane fuel, as such fuels are less prone to detonation. Some modern high performance engines are actually optimized for higher than pump premium (93 AKI in the US). The 2001 - 2007 BMW M3 with the S54 engine is one such car. Car and Driver magazine tested a car using a dynamometer, and found that the power output increased as the AKI was increased up to approximately 96 AKI.

 

i must apologize i mean't No-lead , i miss Sunoco 260 ! and cheap AV gas those days are over

 

There is a way to get cheap and some times free av-gas (aviation Gas)..

When I was working at the airport while I was in college, my ops mgr had a old Benz that he used to run on the sump Jet-A, he would take the 55gal drums of sump fuel to his house and let them settle, then use the Jet-A when it re seperated from the water.

We have begun doing this at the motorcycle shop.. There is a FBO at our local executive airport that allows us to pick up their 55 gallon drums of sumped 100LL ( 100 octane Low Lead) as long as we have a replacement barrel for them. we do have to provide them with a reciept so they can prove to derm that they are not just dumping the fuel in the grass. We let the fuel settle and then pump it out of the drums through a differential filter into 55 gal gas docks.

The mechanics run it in their bikes, we give it to friends for their track days.
One of our mechanics usees it in his 240.

BTW... I use 93 oct non-Ethanol.

Just putting it out there... I dont want to cause a debate on how bad leaded fuel is for your CAT or how it deplete the O-Zone...

 

The only thing to be concerned about with 100LL is the fact that it's not originally blended to be a road fuel. All this means is it doesn't have the wide blend of hydrocarbons to ensure easy cold starting etc. Aviation fuels are blended to always be the same, every time. Cold starts aren't a big issue and operating temps are always very consistent for the fuel.
The lead WILL destroy cat converters, so just be aware of that, it clogs them over time, which has obvious performance reducing potential.
I'd consider the practice of using old 100LL rather pointless though, I guarantee if it was left standing around in drums that were regularly opened, that it's octane wouldn't be much higher than premium unleaded. But it would sure be cheap!

 

The FBO that we get the 100LL from sumps 30gal a day before they fuel the flight schools, so we pick up a barrel every 3 days or so.
Those are very vital points, when it comes to using Av-Gas as well as sump fuel..
but we dont run into those issues here.
in miami we dont have many cold start mornings,
I dont have a cat on my car so no need to worry about clogging. and no cat on the bike either...
But hey its free hi octane fuel you cant beat it in my book, for me at least.