RollinThunder

as some of u kno I recently posted that I installed a C&L 85mm MAF system....in the directions that came with the kit they say ...

"As with all high performance modifications, it is recommended to run 92 or better octane gasonline to prevent and potential pre-ignition at light to moderate loads"....

my question is what does that excatly mean?...and should I run there recommended octane? cuz I thought that u didnt have to run that high of an octane unless u upped your ignition timing...

I need advice from guys that kno what there talkin about like Dan02GT and others (cant think of ur names)....thanks!

VertStangGT86

You can get away with it but if you've got the extra cash you're better off with the higher octane. You don't have much done so you should be fine with a lower octane, as long as your engine runs fine that's what matters.

SilverGTV8

Here is your answer.

Octane rating is a measure of how easily the air/fuel mixture is ignited. The lower the rating the easier it is to light. That is what you want right? WRONG! Well it depends.

A standard GT motor from ford is designed to run on 87. The car is set-up to eliminate the possiblity of detonation. Detonation is the igniting of the air/fuel mixture before the spark and or it is ignite by the spark plug, but ignites in different spots on the cylinder creating hot spots. As you state you usually don't need to increase octane unless you adjust timing, well that's how ford did it, they retard the timing so the motor doesn't ping.

But because you can add more air with an intake and MAF, you can exhaust the fumes faster and easier, the computer naturally begins to advance timing, because it is not working as hard, until it reaches a knock level, which is detonation. Thus needing to bring up octane.

Now the higher the rating the harder it is to light, but it also controls the burn of the mixture. A lower octane will ignite all over the cylnder, instead of at the spark plug, leading to detonation again. Detonation is bad, it can do alot of damage.

What most people, if you are concerened with the price of 92+ octane, is to try a little 89, run the tank real low put in the 89, about a 1/4 tank and drive it around. Listen to the motor, you will acutally hear a pinging sound, typically up high in the rev band. That is the detonation, time to up the octane. Be advise it can be very faint and almost undetectable at times. But you should notice a change in the power because the computer will try to retad timing when it sense the knock.

Now just because they say 92+ doesn't mean you need it, yet. But if you have an exhaust catback, x/h pipe, intake. 92 or higher would be advisable.

I could have gotten a little more indepth but I think you get the picture.

roundman

Silver you're partially right but not all the way right. Octane is the ability of a fuel to resist knocking, the higher the octane, the more it can resist knocking. older Mustangs were also made to run on 93 octane, like my 88. maybe the newer ones are OK with 87, but I know most 5.0's need 93 octane to prevent knocking. the newer motors do have a knock sensor that detects certain sound frequencies that are precursors of knocking, and the ECU will retard the timing some to prevent the knocking from even being heard if it can. sometimes though, people have increased the stock timing and the computer can't pull out enough timing to prevent the knock from occurring, so here again you might need the higher octane. timing and cylinder pressure under load is what determines if an engine will knock or not. the overall compression ratio is certainly another factor, but you can have 9.0:1 ratio and still get high cylinder pressures with the wrong cam and the motor will knock, so you have to be aware of all you do when you mod a motor to keep it where it can run on pump gas. this includes the piston top design, quench areas, and a lot of other high tech stuff that racing motor builders have to be aware of when they build a motor.

SilverGTV8

Knock is detontation. And yes compression, cam, advanced timing, etc etc does play a point. but he was asking with his current set-up and the new MAF if it is nesecary to go up in octane.

Like I said i could have gone more indepth but I think he can figure out what the reason is for the higher octane.

RollinThunder

Yo Silver...bro ur the best lol good info I learned alot from ur post...hopefully someday I'll kno enough that u'll b able to learn something from me...thanks man!

MelloYello

I cant find 92+ anywhere in my city!!!!!! 91 is the highest......

Krusher

very few companies sell 92... newer mustangs (V6 and 281 SOHC) engines in general have been designed to accomedate the 87 octane gasoline, even with light bolt ons... including a new MAF housing. Now here's where it gets tricky... do you need a higher octane with only a few bolt ons? No, not really. Will it hurt? This is still being researched... some say possibly, other's say not a chance. I say run regular to mid-grade... 87 & 89 should be fine for you until you start doing modifications that will significantly change your intake charge, exhaust, or fuel pressure... once you do those... you're going to want to run 91/92 & 116....

You don't really need to burn a hole in your pocket running 91 unless you juiced or blew that thing... that's my opinion.

Sidewayz6.0

This is really something that needs to be decided on a case by case basis. If you're not sure, put 87 in it and hammer it a few times. If you hear it ping, then you need something higher.

The problem with that is the newer cars have a knock sensor (as stated above) so you'll probably have to pay attention. It may retard the timing so fast you won't be able to tell.

Dude...Everyone sells 92. It's 93 thats hard to find. Usually only at an Amoco or Shell. Bigger places like that.

Krusher

oops... sorry... i don't buy the premium.. didn't recall the octane level... thanks sidewayz.