91 Octane Required Vehicle Question?

Question

I am considering buying a vehicle that requires a 91 Octane Rating. What would happen if I ran the regular gas at 81?

The Car in question is a 1996 Cadillac Deville

I meant to type 87 instead of 81

Answer 1

If the car requires 91 octane you MUST use 91 octane in the vehicle.

The reason for the higher octane numbers is to reduce what is known as spontaneous ignition. (Commonly called engine knock)

For a car to run optimally, a flame front needs to be in the proper direction. Typically the flame front is in a radial direction away from the spark plug.

With high compression engines (to get more power which is usually found in luxury and sports vehicles), gasoline in the cylinder can reach temperatures that will cause spontaneous ignition in various places inside the cylinder. These other flame fronts will collide with the flame front coming from the spark plug, and usually results in what is commonly known as Engine knock. This is the sound you hear then the flame fronts colliding with each other.

The shock waves generated WILL cause engine damage and excessive wear over time.

I'm sorry to say, but if you can afford a Luxury vehicle, you need to spend the extra money for the higher performance gasoline to prevent engine wear.

If you think about though your premium gasoline is only like $0.10 more per gallon. At a 15 gallon fill up, you're really only looking at $1.50 more in gasoline. Is $1.50 per tank really soooo much more? Use the Premium gas and save your engine. You'll save money in the long run.

Answer 2

Most of the time if you do not have a turbo you wont have too much of a problem. The pre detonation thing does however occur with low octane in some vehicles. I haven't seen alot of 81 octane fuel. where i lIve in TX they only have 87, 91,93 usually. In fact ive never seen 81 in my life. How ever i have ran 87 octane in vehicles that the owners manual stated a requirement for 91. If the vehicle has an electronic engine management system on board it will automatically adjust the ignition timing in order to counter any knock that occurs from pre detonation. On another note a Cadillac may look nice but they are very poorly made. I would consider getting something else.

Answer 3

regular gas is 87 octane ,,and it will run OK on it,,you wont notice any difference probably at all on it,,as far as power goes it will be about the same on it,,you can at least try it,,and see how it does,,my service truck says to run 91 octane in it,,and i have never done it,,and it runs fine,,and i have no problems with it,,i just save money when i fill up that's all,, i own a repair shop,,and a lot of people have discovered that running a higher octane doesn't help them at all,good luck with it,i hope this help,s.

Answer 4

I would not risk it ! Perhaps you would not hear any engine noise, but the engine could still sustain damage over several ten thousand miles. If you have to use lower than 91 Octane, better go to auto parts or wal mart and purchase some Octane Boost. Let's keep this Cadillac a Cadillac.

Answer 5

Put a few gallons of 87 octane (regular unleaded) in it and see how it runs. If you hear a lot of pinging when going up hills or when the engine is under load, you need to run the higher octane 91. If you don't hear any engine rattling, then drive on, all is well.

Answer 6

For the most part, those above have given you pretty good information and advise.
That said, there is one thing to keep in mind; the PCM for the Cad has programming in it that when detonation is detected (via "knock sensor"), the ignition timing is retarded until the knock is no longer detected. It will try to advance the timing again until it detects knocking, then again retard. No real damage will be done as long as the knock sensor circuit does not fail.
Best advise is to use the fuel that is called for by the owner's manual or the decal on the fuel door.
For a more complete discussion of octane, go here----->http://auto.howstuffworks.com/question90.htm

Good Luck

Answer 7

I have a Saab that requires premium. According to the manual, what happens is that the lower octane gas can cause knocking, which is very bad. In order to compensate the engine compuer retards the timing to prevent this. My car is an 03, I don't know how an 06 handles it.

Either way, it is recommended that you stick with the octane rating your engine was designed for

Answer 8

nothing mine requires 87 and i put 81 in all the time the higher the octane will jus give u better performance

Answer 9

Do you mean 87? I could be wrong. anyways, you needthe hotter burning and faster combusting fuelin order for your timing to be right and for the car to run up to spec. You would probably end up wearing that engine out faster than normal also from all of the misfiring in the cylinder. That puts pressure on your rods and lobes you don't want to throw a rod, If the car is a knockin to come a ..... Well i tried hope i helped!

Answer 10

Regular is 87. And, it would probably ping, which isn't so good for the valves.

??? Where are you guys getting "81"?? I don't think that there is such a thing.