The Barst

Question:
Does octane effect A/F readings? e.g. If I did a run (dyno)and took a a/f reading while on pump gas, would that reading be the same if it was made on 110 octane?

If it changes, how is it affected? Like, if I tuned for 12:1 on 93 octane, what would the a/f look like with 110 octane?

themacuser.org

I'm looking into it. I've never really thought about it before, but I'm curious too..

themacuser.org

'eh - I can't find anything. Fuck google.

Anways - I would imagine you'd run richer with the 110 since more of the fuel would go unburned (since it burns slower, duh), but I doubt the difference would even be noticable..

To0C0oL

i'm not too sure on how it effects your a/f ratio, but i do know that putting some 110 in at the strip and running right then and there, really isnt doing much.. for 1, the computer isnt used to the new gas being burnt yet, and 2, the whole reason to put high octane in, is to being able to advance your timing.. ive seen a few people do it, but most dont.. it may help a little bit, but not as much as it can.. and to try and answer you question from just basica knowledge, i dont see a reason for it effecting it.. the injectors/pump arent pumping more fuel into the cylinders, the fuel just has a lower?? flash point.. thats just what i would assume.. spic's lookin it up so i could be wrong..

themacuser.org

haha - no, that's exactly how it is. The only way it would affect your A/F is by burning slower, so not as much fuel burns, but I doubt it would be noticable. There's really no reason for it unless you're upping the oxygen to go along with it...

The Barst

ok, here is the reason I ask. I want to be able to run race gas allowing me to turn the boost up a bit when needed.

I have a dyno session coming up and was wondering if I can just put the race gas in, hop on the dyno, make a few baseline runs, and then up the boost until I hit the desired a/f.

I want to know what my normal a/f is when I'm driving everyday, but I also want to be able to tune the boost for race gas.

If octane doesn't effect the a/f then I can use the race gas for my dyno session. If it does change the reading then I need to just use pump gas to find out what my true readings are.

Bert

this is my personal experience i'm basing it off of. When i first started breaking in my car i ran a mix of 110 octane and 93 octane giving me a calcuated value of 103ish octane. I was trying to tune to car to eventually run 93 octane normally. I also wanted to run a higher octane first to be safer. With my wideband, i tuned the motor to run the 103 octane mix. I raised the 93 octane amount and lessened the 110 octane amount on my next fill up giving me a octane rating of about 97 octane. noticed that the a/f ratio didn't really change. It may have changed but i was looking for any changes over 1/2 pt. I then decided to put no 110 octane in and fill up w/ 93 octane. The mixture was calculated to be about 94 octane w/ the remaining amount left in the tank. my a/f didn't change but i was only looking for changes greater than 1/2 point again. I was tuning full throttle only to 13:1 a/f and was only looking if any point was greater than 13.5 and less than 12.5 and didn't get any dramatic changes. The only difference i got was the my motor would knock above 6000 rpm w/ 94 octane and less. 97octane and greater didn't knock above 6000 rpm w/ the same timing. I tried to retard the timing w/ the 94 octane but just couldn't get the knocking out. I retarded the timing so much that it was pointless to rev over 6000 w/ 94 octane. Personally, i didn't have any changes w/ going from higher octane to lower octane as for a/f ratio. Nothing noticable at least. The only difference i had was timing. The timing had to be changed. Now I also didn't go to a dyno to see which made power. I wasn't worried about power at the time, i was only worried about the motor running safely.

themacuser.org

So you can run all the octane you want, but it won't change your A/F ratio, but too low octane still makes you detonate from irratic burning?

Bert

don't quote me on it... but that is what happened to me. I ran the car w/ 101 octane and 94 octane and the air fuel didn't change. Significantly at least. The motor did knock w/ 94 octane as opposed to 97 and 101 octane. The air fuel may have changed but nothing dramatic. Nothing that i thought worth noting for. +- 1/2 point.

themacuser.org

Oh no, that's what I've been trying to say from the beginning, I just have nothing to back it up with.. 'cause I'm dumb.