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# does stoic afr effect wot

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Discussion and questions related to the course Understanding AFR

Hello,

I would like to know if the stoic of 15.5 afr will effect the wot target lambda of .88.

i checked both of the reading of the wideband with 14.67 and target lambda of .88

and 15.5 but there is no changing in the wideband both of them reading .88

15.5 * 0.88 = 13.64

14.67 * 0.88 = 12.90

I guest if someone already test this on the dyno maybe he will tell the result of both of them.

The nice thing about working in Lambda is that the stoichiometric value of the particular fuel is not relevant. 0.88 Lambda is a good initial target for WOT on a normally aspirated engine.

There may be some confusion there, for the same fuel, the AFR and lambda is a direct correspondence, as the AFR is calculated from the lambda value. This means you CANNOT have a lambda of 0.88 and different AFR values - for petrol/gasoline that 0.88 is an AFR of 12.94*

Or are you asking if using different fuel blends, with different AFRs for stoich' will affect the lambda? Yes and no...

If you make no other changes, so the same mass (amount) of different fuels are being mixed with the same amount of air, it will indeed change the lambda. NOTE, a common point of confusion is when a gauge reading AFR, calibrated for petrol/gasoline is used with a different fuel - it DOESN'T read the true AFR, but what the petrol AFR would be for the lambda value it's receiving.

Getting back to the 0.88 lambda you mentioned earlier, if you look at the chart linked below, that corresponds to different AFRs - 12.94:1 for petrol, but if you look at the E85 that would be a true 8.59:1 - a gasoline AFR gauge would still read 12.94, though.

Or did you mean something else?

I'm changing the stoic afr to 15.5 ( 1.05 lambda ) for better fuel economy.

and there for i would like to know if it effecting my wot target which is 0.88 ( stoic before adjustment 14.76 * 0.88 = 12.90 )

I wouldn't think so, as it's good practice to run a little lean under light/cruising throttle and progressively enrichen as maximum torque is approached - but I'm far from an expert. For those that are, what vehicle and ECU are you working with - they may be able to offer exactly the help you may need setting the parameters?

My question for general tuning.

i reflash stock ecu as Toyota & Lexus and some Chevy cars.

i hope someone could confirm if the stoic afr will effect the wot afr.

There is no such thing as adjusting the "stoich AFR to 1.05 Lambda". Stoich is ALWAYS 1.00 Lambda.

I think what you mean is that you will adjust your cruise AFR by leaning it out to 1.05 Lambda so you get better fuel economy while driving at a constant speed on the road. Am I right?

Of course, there's a multitude of OEM ECUs that do their calculation differently, but generally speaking your ECU will not be accessing the same areas in your fuel (or MAF calibration) tables when you are cruising and when you are WOT. So no, if you lean out your cruise AFR to 1.05 without touching the area that the ECU is accessing when you are in WOT, it shouldn't affect the WOT AFR.

Thank you Frank,

I actually having this option for Toyota cars.

i did manage to change the stoich to 15.5 and i got a good fuel economy and the Narrow band reading the same as commended afr 15.5 at idle and cruise and light throttle.

at wot im targeting .88 Lambda.

Yes you are right the ecu will not accessing the same areas in fueling at wot but i got confused because of the below formal.

stock stoic 14.6 * 0.88 = 12.85

Tuned stoic 15.5 * 0.88 = 13.64

The same option the GM ECU, but their stoic never goes leaner than 1.00

Yes, you can adjust the stoich value in AFR, but not in Lambda. Right now you are telling the ECU that you will be using pure gasoline.

This table seems to be for ethanol percentage, is it? Around 85% the cell value it’s 9.7?

Yes that's for ethanol percentage, but this pic only for example.

Around 85% the cell value it’s 9.7? Yes

I think I understand what you're trying to do Abu...

Screenshot looks like HP tuners, which I am not extremely familiar with their software. I think frank is correct and that table is for ethanol percentage.

Leaning out the entire map(s) by 5% will remove fuel from areas where it actually needs it (WOT, high load areas, etc), not actually sure what that would do for cold starts. While and AFR of 13.64 isn't likely dangerous for inducing knock on its own, the benefit of the richer AFR the factory was using (12.9) aids in cooling.

Obviously this will require real world validation to determine if it will work for the short or long term.

I personally would not go about changing that particular table and instead re-tune the base target table in the cruise and maybe idle area's of the tables. Not sure which cars or ECU's but I can guess its a MAF based calibration. The way you've suggested feels like a shortcut that will result in various other comprises, but without trying it I really can't say that with certainty. You're altering a fundamental piece of the fuel model.

Mixing AFR and Lambda in this way is confusing. You not changing stoich of the fuel, you are changing the ECU's lambda target. Lambda 1.0 now becomes 15.5:1 AFR. I believe this would affect the entire calibration, but HP tuners would probably be best to answer that.

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