AFR

[tjc]

I understand the purpose of the AFR gauge and what it is, but now I have a couple questions.

1. Will changing the fuel octane charge the reading? As in same setup, same boost pressure, ect? Only change is 110 octane fuel vs 91 octane.

2. Will an intercooler affect this reading? Lower temp denser air?

3. Will timing change the reading?

4. Is it safe to assume if your ratio is in the "safe range" you are good to go?

 

[Omega_5]

I'm going to answer the following assuming you are using a fuel / ignition controller based off a map sensor and rpm.

1) Changing octane *shouldn't* change the afr.
Now, this depends on the type of fuel as well. Ethanol has a lower stoich burn than pure gasoline, but a higher octane value. So keep in mind that your AFR will need to suit the fuel you're using. It's this situation where I prefer to use lambda over AFR.
As well, it's worthy to note that a higher octane fuel burns slower, so it can give a higher AFR reading a low load situations, as the combustion process doesn't always complete in the cylinder, and carries into the exhaust.

2) This depends on your setup. Is the IAT sensor in the upper plenum, or just hanging in the ambient air? If not, the temperature difference can affect how the controller injects fuel, thus affecting what your AFR gauge displays.

3) Typically, timing does not affect AFR in the engine. With that said though, like the higher octane fuel, more timing can delay the combustion event, and affect what your gauge reads.

4) There are two big killers of engines; lean mixture and detonation. From what I've seen with a lot of the fuel systems out there, a lot of the boosted machines are running safely rich. As long as you're in the safe zone for AFR, and the engine isn't knocking, you should be good to go.

 

[tjc]

I was going to hang the stock sensor for the air temp in the ambient. That is what most people have done from what I see.

I will be using a piggy back (gems for now) just 6 psi boost to start.

Thanks for the info.

 

[Omega_5]

I was going to hang the stock sensor for the air temp in the ambient. That is what most people have done from what I see.

I will be using a piggy back (gems for now) just 6 psi boost to start.

If you're hanging the IAT sensor to ambient, the ecu won't be able to compensate for the addition of an intercooler.
This isn't a bad thing, but you will need to monitor the AFR and compensate on the GEMS as needed if you add one in the future.

When changing the controller, be sure to do a few runs at slow speed, and a few at a high speed. The difference in load and air across the intercooler fins will affect how much it cools the charge air.