luneytune

Technical Question on the FD.

What is the minimum octane # you will use?

Will you read a difference on your A/F Gauge with different octanes?

I almost always use 94. Only when I can't get 94 I will use 91 or 92, I haven't seen any different readings on the gauge and I'm not willing to try 87 and see if it makes a difference.

c00lduke

What kinda A/F gauge are you using? Most aren't worth a damn but guessing i think that the higher the octane the richer the mix with come out and same with low octane.

~LUke

Tim McCreary

The octane number is simply a measure of how good the gasoline is at resisting detonation (knocking/pinging).

Detonation (pinging/knocking) occurs after the fuel is ignited by the spark plug, but before the flame front has finished moving across the cylinder to burn all the fuel/air mixture (don't confuse it with pre-ignition, which occurs when the fuel is ignited before the spark occurs).

Going lean in a rotary increases the temperature, which increases the chance of pre-ignition causing the rotary to die.

Please read this very very good article about Octane ratings:

http://chemistry.miningco.com/gi/dyn...M%26s=502%26t=

You can get there from here also:

http://chemistry.miningco.com/librar.../aa070401a.htm

Just go to the bottom and click on Octane Ratings.

Oxygen sensor tells you when you are going lean and introducing pre-ignition. Temperature increases due to going lean can also cause detonation of lower octane fuels even if pre-ignition does not occur.

Tim

luneytune

I know all about octane and its effects, I have read many an article.

But the route of the question is will your A/F gauage read a different ratio with different octane fuels? The zirconium type oxygen sensor to the best information I have will measure oxygen therefore fuel ratio only within a very tight temperature range unless heated as some. Now if we lean out the mixture at some point detonation will occur. If we use a higher or lower octane fuel that number or ratio will be higher or lower.

The question is will the octane change the reading on the gauge or just the point where detonation occurs? If the gauge doesn't change, can we quantify the ratio to a number for each octane?

Zoomspeed

I thought octane had no effect on what your a/f ratio actually is. Not true? Isn't a gallon of 89 octane the same as a gallon 91 octane if we ignore the anti-detonation porperties? So wouldn't your a/f ratio be the same?

I don't know though