What is AFR on a stock C7 Z06 LT4
 

Hi, i need your help regarding AFR on a C7 Z06 LT4. What is the Air fuel ratio on a stock C7 Z06?
I can’t find what AFR is on the direct injection LT4.
I am planning to some mods on my car so I need that information. I know that direct injection has much leaner AFR then port injection but what is AFR on a LT4? Thanks in advance for all help / information I can get from members on this forum.

at full throttle 12.4-12.5 (assuming 14.68 stoich) except for when it injects extra fuel to keep the cats cool, which is almost always, pushing it into the 11s or in some cases even 10s.

at part throttle it runs at stoichiometry in closed loop like all other mass produced vehicles. That is 14.1 on E10, 14.7 on E0, or if you fill it up with something else, whatever stoich is for that particular fuel.

My 2017 commanded is 11.85 at 6400 rpm in PE. Stoich = 14.1(E10) with an EQ Ratio of 1.90. Leaner as I come down in rpm. Never checked it with my wideband before I started modifying so don't really know actual.

Thanks 8850 and Higgs Boson for your answer. I haven’t planned to do any complicated mods for the moment. It’s just a CAI, Katech ported OEM throttle body and Borla X-pipe (that removes the secondary passive cats).

I was hoping that original factory tune is sufficient to manage these minor mods.

But I am also planning to attach a wideband sensor before one monitored primary cat, so i can see what the AFR is after these minor mods. That’s why I need what OEM AFR is for the LT4 so it’s not to lean AFR after my minor mods.

Thanks for your answer. I haven’t planned to do any complicated mods for the moment. It’s just a CAI, Katech ported OEM throttle body and Borla X-pipe (that removes the secondary passive cats).

I was hoping that original factory tune is sufficient to manage these minor mods.

But I am also planning to attach a wideband sensor before one monitored primary cat, so i can see what the AFR is after these minor mods. That’s why I need what OEM AFR is for the LT4 so it’s not to lean AFR after my minor mods.

Thanks for your answer. I haven’t planned to do any complicated mods for the moment. It’s just a CAI, Katech ported OEM throttle body and Borla X-pipe (that removes the secondary passive cats).

I was hoping that original factory tune is sufficient to manage these minor mods.

But I am also planning to attach a wideband sensor before one monitored primary cat, so i can see what the AFR is after these minor mods. That’s why I need what OEM AFR is for the LT4 so it’s not to lean AFR after my minor mods.

If WOT fuel ratio is 12.4-12.5 on E0, what's it at on E10?
 

For the members running E10 what would the stock full throttle AFR be?

We should all really be speaking in Lambda when it comes to any Ethanol content. E0 has a stoich value of 14.7 but E10 has a stoich value of 14.1. You can determine AFR from Lambda based on the stoich value if the given fuel.

Well for those who do not have a chart what would it be? Thanks

lambda doesn't need a chart.

all fuel is lambda 1.0 for stoich
PE is .75 - .9 depending on the fuel and what you're doing with it, engine combo, etc.

on the LT4 PE lambda in the .8 - .85 range will work best, but you need to pinpoint that yourself at the track or dyno, etc.

Looking at my notes from the forum.
 

* 14.7 Lambda (E0)

* E10 correction factor = .959

* 12.4 X .959 = 11.89 AFR

So a 14.7 lambda at 12.4 afr comes out to 11.89 afr running E10 gas.

or

12.4 / 14.7 = .84 lambda

.84 * 14.1 = 11.84 AFR

when your fuel can be between 14.08 and 14.7 AFR but your wideband interprets Lambda 1.0 Stoich at 14.5 and another one interprets it at 14.68 and the dyno itself something else.....who really knows what "AFR" you're running or tuning to......

but if you make it easy and PE is a 20% enrichment from stoich then it's 20%. then you start tuning your car based on your own car rather than just comparing arbitrary AFRs on the internet.

My rule of thumb for the LT4 is basically .5 less AFR for E10 as opposed to E0.
Thats what the numbers work out to anyway.
However E10 "can contain up to 10% Ethanol" so it varies in the real world and can be anywhere in between the two for any given fill up.

If you have a wideband sensor you set it for regular gas regardless of the e-content. The wideband sensor reads it in Lambda and converts it to your selected display fuel, so you can keep the reading to what you are most familiar with regardless of the fuel. Wideband sensor= lambda sensor.

Thanks for your input!

I appreciate the review but that was not my purpose of the comment. Gen V ECU's use a sliding stoich scale based on ethanol content so my comment was geared towards the assumption of tuning the Air Fuel Ratio which is easier done if you work in Lambda.

Thanks for your input!

Its less confusing going off Lambda if you over think it. It’s easier to use AFR if you only have that type of wide band already installed in the car. I have used both AFR/Lambda running E85 in my Camaro and Neon. The Gen V ECU’s use AFR so it’s still easier IMO to view your commanded AFR in the ecm and see if it is matching the AFR gauge that you most likely have anyway when tuning. The flex fuel table in the ecm also uses stoich values in AFR for any given e content.

-Point being, both will get the job done.

I guess we just see a little differently. I find it much easier to work in Lambda when tuning E85 or any non E0 fuel. :cheers:

This illustrates the problem exactly. A wideband AFR will show a preprogrammed stoich value so if you are running E85 with a 9.8 stoich value and the wideband shows 14.7 at stoich, wouldn't you rather it display Lambda 1.0 for stoich at all times?

AFR is a conversion, Lambda is a raw value. A wideband, an ECM, a dyno, etc will all show a different value for AFR stoich but will all show 1.0 for Lambda stoich.