Afr's

[Blown Up]

Can different types of fuels effect afr readings? It seems that when I mix in 110 the afr's lean out a little compared to just running straight 93. Was just curious if type of fuel can effect them.

 

[nate007]

Fuel most definitely effects AFR's. When the ammount of available btu's from any given fuel is different, it requires varying ammounts of it to achieve a certain AFR. The variances are more drastic when you get in to the alcohol blends, but any fuel will change AFR's to some extent. You should always choose the best fuel for your application, tune for that particular fuel, and try to stick with it.

 

[nightrunner06]

i noticed it reads leaner on my mpi charged nytro when i add 110 also

 

[ghost rider]

i noticed it reads leaner on my mpi charged nytro when i add 110 also

Probably due to the lead...

 

[kviper]

So would going from 91 to about 95 octane make a notice able difference in AFR's.

 

[ghost rider]

So would going from 91 to about 95 octane make a notice able difference in AFR's.

Personally I have not measured any difference unless it's leaded fuel....
Even then it's not a big drop.
I don't run ethanol fuels only 94 shell pump or leaded race fuel 110-118
I'm no expert unlike A lot of guys on this site- Just my 2c

Barry

 

[rxrider]

Race fuel is often oxygenated.
It Does burn more completely compared to the junk pump fuel sold in the USA.

 

[Yamadog]

When I do a 2 gallon blend with 8 gallon of 91 I get 10.9 to 11.2 and when I accidentally have more 110 in it 11.1 to 11.5.

I know the higher the octane the slower burning it is and if your timing is not changing you not getting a full burn from the higher octane so the reading will rise a bit. Lower octane ignites faster under heavier compression and will burn more completely giving you better AFR #'s but the knock (premature ignition) will blow you up.