Thread: Ethanol Content and AFR
02-12-2009, 02:12 PM #1
Ethanol Content and AFR
If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.
This can be calculated:
sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)
For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13
So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:
new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio
An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend.
02-12-2009, 02:29 PM #2
- Join Date
- Aug 2006
- Gonzales, La
Cars have O2 sensors, so they can tell when an Ethanol blend is being run. They also apply the fuel correction at full throttle even though they ignore O2 readings then. Conversely, our 4-tec's are "running blind" to the AFR. Putting in E10 will simply make them run leaner all the time.
02-12-2009, 03:45 PM #3
out here in cali all fuel has 10% ethanol
02-12-2009, 03:48 PM #4
02-12-2009, 06:20 PM #5
yup... thats what I did. I wish we could get some of that good 93-94 octane stuff out here!
02-12-2009, 07:00 PM #6
VP Race gas:
MS93TM (unleaded & Non-Oxygenated)
Designed for lower compression engines in racing series that require a cost-effective controlled fuel. Spec Fuel for ASA, Pro Truck and Rmax Challenge.
- Color: Blue
- Motor Octane 90
- R+M/2: 95
- Specific Gravity: .760 at 60° F
02-12-2009, 09:46 PM #7
02-12-2009, 11:04 PM #8
Telephone the above for a local dealer.....oh, and the stuff won't be cheap!
Or, since you're in or near Jacksonville, make inquiry at the local NHRA track, or speed shops.
There are other unleaded racing gasolines available:
02-13-2009, 12:03 PM #9
Looks awesome but to expensive for just rec riding
02-13-2009, 07:05 PM #10
VP C10 is another good choice....unleaded/non Oxygenated.
The best non-oxygenated unleaded racing gasoline available. C10 does not contain any metal compounds and will not harm catalytic converters or oxygen sensors. Used by national champions in SCCA and IMSA stock classes.
- Color: Clear
- Motor Octane 96
- Research Octane: 104
- R+M/2: 100
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