Hi everyone,

I was wondering if anyone has tried to quantify the difference in power when running 87 octane verses 91 octane? The manual states that the engine would produce less power running lower octane but how much? Any 0-60 comparisons out there? And another question. Does the VVT hold the intake valve open slightly longer into the compression stroke to allow the use of 87 octane?

Thanks

 

87=172 HP

The engine doesn't know what octane of fuel is being used. But if it hears a knock/ping, normally caused by low octane it will adjust the timing to correct it.

 

The amount of power loss when using 87 oct gas is going to vary on a number of situations
1) intake air temperature
2) coolant temperature
3) load

If they're all high, the ECM will dial-in a pretty significant amount of knock retard in response to detonation and that will reduce performance noteceably.

If 1 is low, 2 is normal and 3 is high, maybe some knock retard and a slight decrease.

 

since you're not going to see 172hp under light throttle, the engine will need to be loaded under full throttle. i will bet there will be spark knock with low octane on a high compression engine like the 2.4L. if spark knock is detected, the computer will detune the engine. i would guess a 10 to 20Hp loss under full throttle with the crap gas.

 

well i am no mechanic by far....... but i do know this much..... i use 87 .... tank....... I can step on it and peg it out,,,,, and not once have i heard any ping at all...... i have put 2 tanks of 91 in it..... and personally i DONT see any thing difference..... not saying there isnt but i dont notice it...... The car gets up and go.......dont see any difference in my car between 87 or 91 so 87 it gets.......

 

From what I understand, all engines ping a little - we can't hear it all. If you can hear pinging, well, then you're effed!! Back that old HEI off a bit (for the "old timers!".

Detonation kills engines!!

 

Take your car to a dyno shop filled with 92 octane and make some runs. Empty the tank, then fill up with 87 octane and make some runs.. compare the two. My money is that you wont see 172 HP with either grades of gas.

To insure the data is statistically significant, do each at least three or four times over a few days, to see if there is a difference between day to day runs. See if the $600 you'll spend for many dyno runs is worth the answer you'll get.

 

LOL, I run 87 in my SS.
36mpg 66%HWY 33%CTY
Power sems good as the civics and eclispes dissapear in the rearview.
Even without hypermiling I was getting 28 or more over a tank with 87.
But if you want 172hp in high heat, while going up hill, with a trunk full of luggage at 5000rpm, better use 91....
If this does not describe your normal driving situation
Keep the cash in your pocket.

 

As has been discussed many times before, "your mileage will vary". As far as power goes, I notice no discernable differnce at "street" speeds. But I do notice a marked diffference when hitting the gas hard at freeway speeds. Definatly more power using 91 octane at freeway speeds (50mph and faster).

Some, including myself have recorded better mileage with 91 also. Granted, when the cost difference is factored in, its pretty close to a wash. I save about $100 per year by using 91. But that coupled with the extra power at freeway speeds makes it worthwhile for me. It also runs a bit smoother on 91.

I recommend trying both, for at least a month each, and then deciding for yourself if the difference is worth it. There are so many things that affect power and mileage that no one can say for someone else that they should or should not use 91 ocatane.

 

Of course you won't hear it!!!! The engine has a knock sensor and at the first sign of a knock it retards the timing reducing the power till the knock goes away.

But I imagine that GM recommends 91 octane because they are in bed with the oil companies and want you to give more money to them.