stangs82,93,06

is it a waste of $ to use 93oct?will it do any harm?
i`m going to leave my gt stock.if the will run better on 93 i`m willing to spend extra $. thanks

cyoon

Using anything other than 87 octane is a waste of money. It doesn't improve your gas efficiency or give you more power since the mustange was designed for 87.

ManEHawke

Unless you use a tune, but without one you're actually risking it to ping.

WERKED 66

i put in 93 without a tune and did see more pep to it..did not have a pinging issue at all...

ManEHawke

The engine is timed to accept the faster burning 87 to make it's maximmum power. Sure the car will adapt a bit with 93 since it's computer controlled, but it won't make more power. You will need to time it for a faster fuel burn.
The fact that you put 93, and it ran smooth, may have phsycologicaly made you think you got more pep. Same as people who put a louder exhaust, people who use tighter springs that show no real world handling improvements.

Shifty

Without a tune: No.

With a tune: YES.

cyoon

I thought that the octane you use depends on the engine compression. Does a tune increase the compression? I don't think higher ocane will cause a ping. I think pings happend when you use lower octance on a high octane engine.

ManEHawke

A high compression engine uses high octane to prevent detonation, and so it won't diesel.
You can benefit with higher octane if you time for it.

1 COBRA

I've used 93 octane on four GTs, one Bullitt, two Mach 1s with and without CAIs and aftermarket catbacks with no tunes without a single engine issue. I also never experienced any knocking which is sometimes associated with the lower grade gasolines at low rpms.

ManEHawke

The engine can adapt to prevent knocks (up to a certain point)
What will not happen is a miracle enhacement of power.

What some manufacturers do (not the case here) is they tune to 93, but advise the use of 87 for economy. Owners of these cars feel like they have unleashed power when they use 93. Which is true because they have been using 87 for a car that was designed for 93 all along.
This is not true with the Mustang however.

WERKED 66

you may be right in some cases but i know for sure it had more pep..my girlfriend asked my if i had done anything to the car ...and she did not know that i had put 93 in it..but i have the tune to go with it now

GhostGT

:scratch: Um..have you driven a stock GT, and then a GT with a suspension kit on it? I don't know how you could say that, my GT makes a world of a difference with the kit, and i've driven mine with the stock 17" bullets, too.

^Don't mean to prove you wrong, but there IS a difference in the suspension. And the 93 octane? It COULD have made a difference in the driving habits of the car. I use 91 all the time; once I had to use 87 since that was all the local station had, AND i was getting low. Wow i really felt a difference in the car's behavior.

ManEHawke

I was actually talking in general. Some exhaust systems cut back in a vehicles torque, and in turn increase the sound. The increased sound makes the driver feel likes he's faster.

Same with the stiff springs, there are many "import" owners who stiffen their car up thinking they have improved the handling when in reality they have worsened it.

After reading that it may have sounded like I was talking about the Mustang and mods people put on here, but it was actually a general statement.

As for the gas I'll have to study up some more on this ECM to see if it is possible for the Mustangs computer to adapt so well to see an increase. Untill then I will remain sceptical, but I'll buy it for now.

Sorry for the misunderstanding.

OBleedingMe

WIthout atune, it's impossible to get any gains out of switching over to 93 octane. The computer does NOT automatically adjust the timing enough for that. If that was true, people wouldn't be getting tunes for it. It's all in your head, brother.

nynvolt

Higher the octane, the higher the resistance to burn. In other words the 87 will burn more easily than 93, and higher octane wont make you ping, lower than rated for your car or crappy gas may, because it is igniting before it is supposed to.

I have tried all the crappy grades they sell in California and have actually monitored my milage and performance. I have found no performance change from 87-89-91 and my milage stays the same. I don't even bother with the higher octane anymore. You may experiance a plecebo effect, thinking you should be getting something out of running the higher grade gas but in reality, you don't.

stonecoldtx

Well, there seems to be a bit of a misunderstanding about what an octane rating actually is, and what it does for an engine.

This is really only a general overview of how octane rating can affect an engine, because there is a LOT more to it than what I'll cover here.

First off--let's find out what "Octane" really means:

Per the definition HERE, Octane is the "resistance to detonation". Not to be argumentative, but it is not quite a "resistance to burning".

Now, here is how octane affects engines:

One of the most (if not THE most) destructive things that can happen to an engine is for it to experience detonation, which is sometimes referred to as "Ping" because of the sound it makes.

Detonation, by one of the definitions HERE (paraphrased) is "a violent release of energy caused by a chemical reaction".

What that means when in the context of a gasoline-powered internal combustion engine is that the fuel is burning in an uncontrolled manner, whereas normally it is controlled, and that's what we want--a controlled BURN, not an uncontrolled "explosion".

Detonation many times happens if there is "preignition" which would occur if part of the fuel ignites prior to the spark igniting another part, and the two "flame fronts" collide, and that causes a sharp "spike" in the pressure acting on the top of the piston.

The effect is has is about the same as if one took a hammer and pounded on the top of the piston, and so you can probably see why it has such a detrimental effect on engine parts!!

Now, let's talk about some situations where it might happen:

An engine is designed to operate at a specific engine temperature, using air that is within a certain temperature range, with fuel in a specific ratio to that air, and at a specific octane rating.

Fuel takes a specific amount of time to burn, and the point at which it is ignited in relation to engine speed is calculated so that when that fuel is burned, it is burned completely in a controlled fashion, so as to prevent preignition and detonation from occurring.

The lower the octane rating, the less resistance to detonation it has (some may say that it "burns faster"--I think I saw that statement), the less timing it will "tolerate" before preignition or detonation occurs, with all the other factors being the same.

Thus, if SOME of the factors change, then the point at which preignition or detonation occurs also changes--i,e,: if an engine is hot, it is more likely to cause the fuel on the far end of the cylinder (away from the spark plug) to ignite than when it is cooler; the reverse is also true.

To prevent, or minimize this effect, the factories have spent literally millions of dollars researching, testing and designing these engines and their supporting systems to work with readily-available 87-Octane pump gas, make the most power available and still prevent detonation.

These systems are optomized so that at the optimal air and engine temperature, it makes the most power; there is also a "knock sensor" on most engines (I believe including this one) that, when the system detects detonation occurring, immediately informs the ECM, and ignition timing is "pulled out" or retarded to stop the detonation from occurring.

However, just because one puts a higher-octane fuel in the tank does not mean that it will allow the engine to make more power--it would require a modification to the factory settings to take advantage of the increased resistance to detonation.

Likewise, if there *IS* an increase in power by simply using a higher octane fuel, it would be because the computer system was retarding ignition timing to get rid of "ping" that was occurring with the lower octane fuel.

OK--so, why are there different "Tunes" available for different octane ratings?

SIMPLE--because when you use higher octane fuel, ignition timing can be altered to take advantage of the higher "resistance to detonation" that the elevated octane rating can provide, and allow the timing to be more advanced under conditions where it might "Ping" with the lower octane fuel at that timing setting.

What I've written here is QUITE an oversimplification, and that there are a LOT of other factors involved, but suffice to say that these are the basics involved with octane ratings and their effect on preventing detonation from occurring.

Hope this helps!

The Lyin' King

Nicely done explaination !!! Was this your thesis for graduation ?

I believe the range of timing that the ECM can add or subtract from listening to the knock sensors and reading inputs from the rest of the systems sensors is on the order of 8-10 degrees . . . . using your example . . . being down 8-10 degrees of timing because of crap gas would make a noticable difference IMO.

Shifty

You increase the timing with a 93 octane tune. 9.8:1 is plenty for 93 octane. I'm suprised they can get it to run on 87. My M635csi was 10:1 and it couldn't even run right on 93 octane from this country, needed race gas. Eventually had to rebuild the motor so I put in lower compression pistons.

cyoon

That explaination is true, but since the Mustang was built for 87 octane, I don't think higher octanes would improve performance without reprogramming the car.

GhostGT

Sorry I might have come across too strong. I didn't mean to prove you wrong or anything, but I just wanted to see what you thought about, well, what I thought. Anyway, thank you for being nice .