What happens if 87 octane used on 91 octane tune??

[krehn]

Ok, so I am toying with getting the 91 octane tune even tho my parents would go apeshit if they found out that I was making them pay for 91 octane instead of 87. But my question is, lets say I sneak behind their back and do it anyway, and they borrow my car or something and put in 87 instead of 91. What would happen??

Also, what kind of difference is there between the 87 tune and the 91 tune?

[Hello]

a tune will help you, but putting 91 octane into an 87 octane tuned car will basically do nothing, even though most people say it will help it really doesn't. From all the research and articles I've read if your car isn't tuned for it, don't use it your just wasting your money

[krehn]

I dont think you read my question right. Im not asking about putting 91 in an 87 tune. I am asking about putting 87 in a 91 tune.

[GT-R]

You run the risk of detonating, if it's driven hard.

[Hello]

oh sorry about that i thought you were asking what if you put 91 into a 87 car

[PrimeGTP]

You run the risk of detonating, if it's driven hard.

Sam is correct. Any high amount of throttle and you roll the dice against the big KABOOM.

[Bowtie Boy]

i wouldnt worry about it too much. you gotta figure, your parents probably are not gonna be ripping on your car that hard, and even if it does start knocking, as long as you havent disabled the knock control system on your car (or messed with it greatly for that matter), the ECU should pull timing back. Granted it will go through a process of knock, retard, advance, knock, retard etc. while you have the 87 octane in there, engines can a lot of knock below 3000RPM, and if it is not under heavy loads they can take even more. The reason moderate knock doesnt necessarily hurt an engine below 3000RPM is b/c there is enough time btw each combustion process at the lower engine speeds the cooling system is able to pull the heat out.

I have to run out the door and i am being b($tched at, I will clarify better later.

[Interfire]

The tune will dial back some to compensate, but not all. Just stay away from WOT and you'd be ok.

[ElecBlueG6GT]

I believe there are more than one fuel map in the G6. Blackrider has used lower octane in his Vector tune. I was told that at Vector.
Tell mom and dad that the 6 runs better on 91.

[dre256]

Accally, prob not much would happen besides a performance drop. As the knock sensor would determain the detonation and miss detonation and pull timing. However, in the long run the knock sensor might not fully compinsate for the miss detonation and in a matter of time a few years your could adventally blow a piston if not sooner. Its hard to say

[handyjoe]

If the car is HPTuned, it probably has a High Octane map (the one that should be tuned) and a low octane map, made just in case that happens.

It will pull timing like mad and the car will feel pretty slow, but it shouldn't hurt anything.

[Bowtie Boy]

Nevermind, I dont think I need to clarify anything any more like I was going to. Basically everyone is agreeing that one tank of 87 is not gonna kill ya, I imagine that is enough concensus/proof?

(just for the record, my previous comments regarding knock was in reference to a non-boosted application. too much IG is more likely to become dangerous on a forced induction engine.)

[Beau]

Unless the tuner sucked, There would be no short term effects in terms of damage. And thats if they were going wot all the time. If they are just crusin around, not much would happen, you could still get KR, but at such low cylinder filling at part throttle, nothing would happen to modern components.

[ragingfish]

I'll play odd man out. Why don't you leave their car the hell alone and get your own and tune the shit outta that?

[Six-Speed]

91 octane myth!

Putting 91 octane in a motor running on 87 octane will do absolutely nothing for your motors performance. In fact it will most likely hurt it. You see, octane prevents pre-ignition. Motors that require 91 octane gasoline have a high compression ratio, usually somewhere around 11:1. Most cars have compression ratios of around 9:1. When you have a high compression ratio the gas will start to ignite on the compression stroke even though the spark plug has not yet fired. This is due to the high pressure and heat. As you compress a gas, it heats up. This is how diesel engines work. They don't have spark plugs, but their compression ratio is like 20:1! Also, diesel fuel burns, it doesn't explode like gasoline. If you increase the octane rating in a gasoline engine, the gas will not ignite during the compression stroke until the spark plug fires. If you have too much octane, and the motor doesn't need it, the combustion of the gas will be retarted and will hinder you're engines performance.