I just got my 85runner today and was wondering what octane they were meant to run at. Right now its dead stock. thanx

since i bought mine about 2 years ago i run it with 85.5 octane. there is a little adjuster under the distributer to adjust the octane you run in the motor, it adjusts the the retarting of the spark.

my motor actually has more power with the cheap gas and gets better gas milage.:confused: its wierd but it seems to work. i never have pinging either. this motor is just solid. it has 145,000 mile on it and its an 85 with fuel injection.

although in my manual it says to run atleast 87 octane.

Higher octane wont give you more power anyway....unless your motor is setup for it. The reason that some vehicles run better on higher octane is because the motors are experiencing pre-detonation or "pinging". They need the higher octane because it has a higher flash point and doesn't let the cylinder temp & pressure ignite the fuel prematurely.....thus giving it a more efficent burn which equates to more power.

I try to run regular in everything but sometimes I cannot. My hybrid needed premium because I was running 10.5:1 compression and 28* base timing. The motor screamed but if I put even 89 in it, it would ping to beat the band.

damn newbies :flipoff2:

Originally posted by Chad
The reason that some vehicles run better on higher octane is because the motors are experiencing pre-detonation or "pinging".

there is No Such Thing as pre-detonation. :rolleyes:

my 2000 celica gts has a 11.5 compression ratio and has to run 91 or higher or it pings really bad and just flat out runs like shit.

Originally posted by bgreen


there is No Such Thing as pre-detonation. :rolleyes:


You better do some catching up on the terminology of auto mechanics. Pre-detonation or Pre-Ignition IS in fact a real and very common issue with vehicles. If pre-detonation/pre-ignition didn't exist, I wouldn't have learned it from my GM schooling and I wouldn't have needed to know it when I became ASE Master Certified.

What do you think pinging is??? IT is the air/fuel mixture pre-detonating or pre-igniting. Do some searching, you'll find the answers.:flipoff2:

Get it straight before you start trying to sound like a bad ass. Detonation and Pre-ignition are two completely different things. :rolleyes:

You better go back to school :eek:

OK...I'm know what I'm trying to say...just not saying it properly. Yes they are two different things but they go hand in hand.



Abnormal combustion is know as Detonation. It is also known as "engine knock" from the noise that is transmitted from the colliding of the multiple flame fronts and the increased cylinder pressure that causes the piston, connecting rod and bearings to resonate.

Preignition is caused by an improper octane level which determines a fuel's ability to resist auto-ignition, or in lehmans terms, its ability to wait for a spark to initiate a flame. When this happens, the heat from a hotspot on the piston causes the fuel to ignite before the spark plug fires. Then when the flame from the piston meets with the flame from sparkplug, you get your knock.

When you have a preignition situation, you will have detonation. 95% of detonation is audible. But just because it is not audible, does not mean it is not happening. You could still be chipping away at the pistons from the preignition.

Why would I want to be a bad ass? I just want people to know the facts.......it's people like you that help me state them correctly! :beer:

Glad I could be of assistance. he he :D I could be wrong, but here is what I understand of the topic at hand:

Pre-ignition can be caused by several factors, one being hotspots caused by carbon build up, sharp edges on vavles, spark plugs, and valve reliefs, ect. These hot spots can cause the fuel to start burning prematurely.

Detonation can be caused by several things as well, but I would venture to guess that its usually caused by too low octane level and/or too high compression ratio. Both causeing the fuel to burn to fast.

There are many other factors involved, such as timing, combustion chamber characteristics, fuel/air mixture, ect, ect.

I am by no means any kind of expert, but I have been doing this kind of stuff since I was about 8.

Next....:p