In Minnesota it is supposedly illegal to fill up with premium 91 octane gas unless you have a classic car that needs it. I don't think they would do alot for using it, but i don't use it so i have never found out.

 

Larson, I wonder if you could scan your car and read the Knock Sensor and/or Knock Retard. You may be better off adjusting your timing than taking 10* Ignition Timing Retard if you are getting any pre-ignition. You may not be able to detect it by the seat of the pants feel... but you may be getting knock retard.

Don't jump on me guys, the ignition system will compensate for any pre-ignition (auto-ignition). I've never tested a car with 87 Octane and I'm just curious.

 

I live in Minnesota and I have never heard of this. Where did you get this info.

I have ran 87 in my 95 once and it ran like POOP. I have run 92 or higher ever since and it loves it.

 

Especially in the summer, my car "feels" fastest with 92 octane.... i've tired 91 and 94 as well.

With older cars, there is also the issue of "Octane creep"... basically as the car gets older, it requires higher octane... something to do with carbon build-up or something.

I did use 89 over the winter though... power wasn't and issue in the snow and skinny winter tires.

Just went back to 92 as I put on my summer tires and want the power back.

 

i used 87 once, whenever i let off the throttle i would hear "pop, pop, gurgle, gurgle"

and when you have a full tank of 87 the car runs like the v-6

 

So basically it sucks to use 87 gas but anything higher than 91 wont be any better than just filling up with the 91?

 

according to GM on a stock car...

 

under what circumstances would u want to use more than 91 octane?

 

when you are trying to prevent detonation which occurs more easily the higher compression there is (and boost)

 

Also, about the older car requiring more octane... you are correct. Depending on the condition of the engine. If there is a LOT of carbon build up in the manifold (Carbureted Cars) and on the back side of the valves, the carbon will SOAK up the fuel like a sponge creating a lean mixture. To reduce detonation because of the lean mixture, a higher octane is needed.

Better yet, get some Seaform (or the like) and a tune-up.

 

You may consider them fancy words, but they are NOT synonymous. Detonation and pre-ignition are two distinctly different types of "combustion gone astray". With pre-ignition, the mixture ignites BEFORE the spark. It is a result of auto-ignition of the normal fuel components. Not good for your engine, but generally less destructive than detonation.

But detonation occurs when a second flame front develops AFTER the spark, and involves auto-ignition of end-gases, not the auto-ignition of the normal gasoline components. Subtle difference, but critical in understanding the differences between pre-ignition (ping) and detonation (knock). Because of the huge pressure surges caused when the two flame fronts collide, detonation can be truely devastating on the engine components. I'd say 95% of the problems people are running into are detonation, and not pre-ignition.

My point was not to confuse anyone with "fancy words", but simply to explain that the assumption that higher octane somehow means slower flame speeds, the foundation of the initial post to this thread, was incorrect.

 

all cars are a little different so you all can take that into account here.

watching a real time scanner(Scanmaster) i have observed part throttle knock retart using 87 octane Conoco gasoline. when i use 91 octane Conoco gasoline i notice zero knock retard at part throttle and only occasionally some in the upper RPMs. the difference is probably too subtle to feel at part throttle or just cruising around town but on a dyno or even at the track the affects become more apparent.

 

Injuneer, my apologies. I read it as auto-ignition to mean the same as pre-ignition. Since auto-ignition is part of the equation related to detonation it makes sense.