e85 question

[gtpsleeper]

im searching around looking for ways to run leaner while cruising and am wondering why i keep seeing people change from 14.7 to 9.8 and such for their afrs? can someone explain why because it doesn make since to me? wouldn that make you pig rich? did i miss something here?

again this is for just e85...

[Boosted3Bar]

I don't understand it either, mine is still 14.7 afr. Narrowband only reads lambda, not actual afr, so in my mind 14.7 afr equals 1.0 lambda which is 9.87 on e85. My wideband reads ~10:1 at cruise so I know 14.7 works.

[Google]

E85 does not have a stoichiometric ratio of 14.6 to 14.7 like gas does. E85 stoichiometric ratio is in the 9's.

Lambda of 1.00 is the stoichiometric ratio, gas or E85. Do more reading of stickys or get Gregs book - DVD, or the Tuning Schools Class.

[gtpsleeper]

read every sticky i could find on it and still dont understand it all that great... especially when we V6 guys cant change our stoich settings unless were in open loop anyway so I dont see how it would make a difference what we put in there is what i mean...

[BlackGS]

The best ratio for gas mixture is 14.7 parts air to 1 part fuel.
The best ratio for e85 mixture is 9.8 parts air to 1 part fuel.

The O2 sensor does not know how much air or fuel you started with. It only knows oxygen levels left in the spent charge. The O2 sensor reports in terms of lambda. If the lambda value is 1.0, the fuel is burned optimally, and started with the right mix. Whether you start with gas at 14.7:1 or e85 at 9.8:1, the lambda will be the same at the O2 sensor.

When you see a value reported from a wideband, the value is typically converted to a gas equivalent AFR. Some widebands (like the PLX) will let you change the display and show lambda, or show ethanol-equivalent AFR's. So, let's say your wideband is set to show gas equivalent AFR, but you are running e85. Cruising around, the display will show 14.7:1. This means the lambda is 1.0, and in reality your e85 mix is 9.8:1. When you go WOT, the wideband display shows 11.76:1. This means your lambda is .80, and if you are running e85, the actual mix was 7.84:1. (Narrowbands work in the same way, but we only see raw voltages).

When you switch to e85, you have to tell the computer to increase the fuel delivery to make the initial mix 9.8:1. If you change the stoich setting in HPT, you must also change other fueling tables to make sure the calculations stay correct. (See this post for more info: http://www.hptuners.com/forum/showthread.php?t=31925). A simpler method is to tell the injectors to just deliver more fuel. This keeps all the other calculations correct, and only requires changing one table. The rule of thumb is usually to start out by telling the injectors to deliver 30% more fuel, and then tweak from there.

To run leaner at cruise, you must work around the fact that the computer is always trying to compensate off the lambda. If you just change injector values, the computer will still try to trim the fuel delivery to meet the stoich value in the closed-loop feedback. That is the big benefit of going all open-loop. You decide exactly how much fuel to deliver based on airflow, not feedback. If you want to lean out and stay in closed loop, follow the stoich changes described in that link above.

[Lumpo]

What spark plugs and gap do you guys recommend me with my setup on E85. I have [email protected] ATM.

[BlackGS]

What spark plugs and gap do you guys recommend me with my setup on E85. I have [email protected] ATM.

That should work fine. I run 103's with a .030 to .035 gap, but I have the turbo.

[gtpsleeper]

The best ratio for gas mixture is 14.7 parts air to 1 part fuel.
The best ratio for e85 mixture is 9.8 parts air to 1 part fuel.

The O2 sensor does not know how much air or fuel you started with. It only knows oxygen levels left in the spent charge. The O2 sensor reports in terms of lambda. If the lambda value is 1.0, the fuel is burned optimally, and started with the right mix. Whether you start with gas at 14.7:1 or e85 at 9.8:1, the lambda will be the same at the O2 sensor.

When you see a value reported from a wideband, the value is typically converted to a gas equivalent AFR. Some widebands (like the PLX) will let you change the display and show lambda, or show ethanol-equivalent AFR's. So, let's say your wideband is set to show gas equivalent AFR, but you are running e85. Cruising around, the display will show 14.7:1. This means the lambda is 1.0, and in reality your e85 mix is 9.8:1. When you go WOT, the wideband display shows 11.76:1. This means your lambda is .80, and if you are running e85, the actual mix was 7.84:1. (Narrowbands work in the same way, but we only see raw voltages).

When you switch to e85, you have to tell the computer to increase the fuel delivery to make the initial mix 9.8:1. If you change the stoich setting in HPT, you must also change other fueling tables to make sure the calculations stay correct. (See this post for more info: http://www.hptuners.com/forum/showthread.php?t=31925). A simpler method is to tell the injectors to just deliver more fuel. This keeps all the other calculations correct, and only requires changing one table. The rule of thumb is usually to start out by telling the injectors to deliver 30% more fuel, and then tweak from there.

To run leaner at cruise, you must work around the fact that the computer is always trying to compensate off the lambda. If you just change injector values, the computer will still try to trim the fuel delivery to meet the stoich value in the closed-loop feedback. That is the big benefit of going all open-loop. You decide exactly how much fuel to deliver based on airflow, not feedback. If you want to lean out and stay in closed loop, follow the stoich changes described in that link above.

^^^ completely understand now thank you SO much!

[xpzd3800]

yes thank you for that. I get it now. might have to go open loop here soon for gas mileage/ lean cruise