AFR?'s when to deviate from 14.7

[DSMmonster123]

Based on rpm and load factor how far can i take a 14.7 afr? I'm using the table with dsmlink to tune. As a matter of opinion when would you deviate from 14.7? Its 2g DD, stock internals with a big 16g. But with a 6cm hotside so it boosts lile a 14b, seeing about 5psi by the end of each gear in traffic about 3000 rpm shift point. I would like to stay stioc for as long as posible for both fuel savings and power.
Also why is the afr at idle so rich? I had to lean it out to pass emissons. Is it rich for a reason?

 

[Calan]

You'll always be targeting 14.7:1 while in closed loop when the car is warmed up. You only need to worry about a richer AFR while at WOT; everything else is a transition between the two for the most part.

You can download the stock or mod1 Evo maps from the ECMLink site, which are good maps to start with.

 

[DSMmonster123]

I understand that part but i'm talking about extending the threshold. Either by extending closed loop operation or setting open loop to stioch. The reason im curious is i just installed a wideband and running a NO2 sim. Its super responsive and keeps the mix tight around 14.7 unlike the stock o2 which was all over the place. Car runs better than ever now. Let me revise the question: at what point does it become necessary to richen the fuel mix?

 

[Calan]

...at what point does it become necessary to richen the fuel mix?

Depending on the type of fuel and other factors, you'll normally want an AFR between 10.8:1 and 12.5:1 while under full load, which means WOT at full boost... where ever that falls on your car. Every other operating point that the engine can hit should be somewhere around 14.7:1, or transitioning towards that full load AFR. You also want to richen things up a bit as RPM increases past 4k-5k or so, even at low loads.

The best approach is to just use the stock AFR map and to lean out the WOT areas somewhat, since it is very conservative. You may also want to modify the turbo's spool area of the map to change spool-up characteristics.

If you are just wanting to improve gas mileage a little during highway cruising, you can raise the switch-over voltage of the NB sim so that it switches over at higher AFR. You won't gain much though, and it can throw off your fuel trims. Or you could lock it in open loop and raise the low-load areas of the map to something like 15.5:1 or so up to about 4k RPMs...but again, you won't gain much and you might actually get worse gas mileage if the torque output drops with the higher AFR.

IMO, better gas mileage and performance comes from ideal timing advance, based on whatever AFR you are running at any given point.

 

[zman8023]

Stoichiometric should only be maintained while under about 100kPa (atmospheric), meaning 14.7 is okay as long as you are out of boost. It also depends on how much torque you are trying to make at lower rpm's, as maximum torque numbers usually occur at ratio's lower than 14.7. So if you aren't trying to make power before you are in positive intake mani pressure, keep it at 14.7, but add more fuel when under boost.

 

[DSMmonster123]

I really disagree with that rule unless your running a huge turbo like a holset or high compression pistons like an n/a. think about the stock turbo, a t-25 is definitely in boost and closed loop at the same time.

What I ended up doing was I took a log while I drove to work. I drove like a sane person meaning no hard acceleration, throttle below 30%, etc. then based on the log I raised the closed loop thresholds so that it began to kick out just before i hit the shift point. i figured i can actually set the load factor thresholds pretty high but keep the throttle position low. that way when i do hit the throttle it kicks out and dosen't blow up the motor. loadfactor is set to 1.4 all the way up till 3500 rpm. but the throttle position is no higher than 35%. i'll probably have to tweek it after i install my cyclone and n/a throttlebody.

 

[jtmcinder]

I, also, disagree with the idea that when to switch out of closed-loop should be set by boost; it should be set by air-flow. In fact, I'd go so far as to say that boost is irrelevant. What matters are how much air is flowing and the temp of said air. Yes, boost plays a huge role in determining both air-flow and IAT, but the level of boost, itself, is irrelevant.

 

[Bohrn]

if you are trying to save fuel, I suggest you go even leaner in your low load maps. Off idle, and low to mid range rpm low throttle areas, I use up to 15.5:1. You can even go a tad leaner, but it gets fussy around there, so you can experiment, but for my altitude and fuel, this seems to work best on the cars I have tuned.

I do the idle cells at 14.7:1 so it idles nicer. With totally stock cams and a 5spd, you can go a bit leaner, but if you have upgrade cams, again, the idle starts to suffer with leaner mixtures. Tho it can sound badass if you like that.

with the cruise areas I start at that 15.5:1 afr then gradually richen it up so that where it transitions to boost, its about 13.5:1 at around 0 boost. obviously it richens up fairly quickly after that. With a quick spooling turbo, you will have to play with it to see where it gives you best throttle response etc.

you also want to work with your timing table(s) to make sure you have enough advance for the rpm/load. Again tho not too much or other things start to suffer.

Each car is different as you know, so no one is going to be able to give you exact numbers, but you should be able to get close with some help then fine tune it as you learn more of how its working.

bit of a disclaimer, I have never used DSMLink, but at the end of the day, adding/subtracting fuel and timing should give the same results no matter what software does it, providing everything is in good working order.

 

[milby43]

I have a question pertaining to this.

If I'm daily driving, maybe 30% throttle, and i start to slighty go into boost. Like maybe 4-5psi vs my max of 15. What should my AFR look like or be close to at that point (low boost, low throttle, maybe 3500rpm..kinda like down shifting and passing someone on the highway. But not going hard on the throttle)

 

[Bohrn]

without knowing your car, your conditions etc, I can only tell you what works for my car but I am thinking roughly around 13.2 down to about 12.8 or so.

at 30% throttle tho, it will easily and quickly go to more boost, and so it will need to richen up. even with my fairly large turbo by 3900 rpm even with only 40% throttle I will still see 25psi or even more.