How to get good AFR targets?

[turbogrill]

Hi

I have a MS2 converted stockish  L28 that I very much enjoy tunung. I run a mix of autotune and manual tune. But currently building a new engine. 

My problem is how do i know what my AFR targets should be for my  L28 build? 

As of now I have tunerstudio calculate it for me based on some generic formula. Works OK but probably not optimal for our engines. 

So how do I find the best afr targets? 

1. Trial and error at Dyno? 

2. Find a rebello engine with similar specs and copy theirs? 

Currently stock but planning on 200whp target.  N47 with Flattops, decent port, mild street) M455 cam (280 advanced duration). 

Thanks 

[spiff]

There's tons of info on this topic around the web, but in short: most engines develop the best performance slightly richer than stoic,  na's around 12-13:1 and turbos around 12, maybe 11, some even richer as a safety measure. 

Idling, most batch fire engines like a slightly rich idle, sequential injection engines can often idle closer to stoic but the important thing is to get a smooth idle, not to chase numbers. 

Cruising can see leaner afrs 15-16 maybe higher as long as it runs smoothly 

[turbogrill]

Hi

I guess what I am wondering is how people find their AFR targets? 

Start with guidelines and then trial and error? 

 

[seattlejester]

Guidelines really. Unless you have access to a good tuner with experience or a dyno to really dial it in. You could ask a local performance shop that has experience what they like to see, although some do treat that stuff as trade secrets. 

[madkaw]

Like said- guidelines . I would stay fat in key areas if heavier loading and go lean as you want cruising . I feel comfortable with 15 at cruise and 13:1 at WOT . 

Timing might be where the tuning might be critical or more critical than the fuel. 

I can post up my tune when I get on my laptop , but I'm pretty aggressive on my semi closed e88 head . I've had no detonation issues so far. 

[Chickenman]

On 10/11/2017 at 8:29 AM, turbogrill said:

Hi

I have a MS2 converted stockish  L28 that I very much enjoy tunung. I run a mix of autotune and manual tune. But currently building a new engine. 

My problem is how do i know what my AFR targets should be for my  L28 build? 

As of now I have tunerstudio calculate it for me based on some generic formula. Works OK but probably not optimal for our engines. 

So how do I find the best afr targets? 

1. Trial and error at Dyno? 

2. Find a rebello engine with similar specs and copy theirs? 

Currently stock but planning on 200whp target.  N47 with Flattops, decent port, mild street) M455 cam (280 advanced duration). 

Thanks 

M455 Cam in Texas. man those Shadbolt cams get around. Still one of the best grinds to this day.. I think Steve is running a Baseline Table that I sent him. He may have tweaked it to further enhance. I'll let him respond, but I have some tables that should work pretty good.

 

[Chickenman]

One thing that will really affect your fueling Tables is if you are using the stock Low-Z injectors and PW Current limiting instead of the factory dropping resistors. The Default TS  values ( 30, 1.0,66 ) do not seem to work well with the stock Nissan 188cc and 260cc injectors. These settings seem to be fine on other injectors though. Unfortunately it's not a " one size fits all " situation and finding the sweet spot for our injectors is tricky.

MS1 and MS-2 can be problematic using PWCL and stock Nissan injectors. The MS-3 units seem to be OK. Mind you MS-3 uses a completely revised Firmware model over MS-2and MS-1. Seems to be a lot better in many aspects.

For MS-1 and MS-2  I would highly suggest using the factory dropping resistors ( or something similar ) or using HI-Z injectors. The difference in the Fueling curve can be quite dramatic. with no dropping resistors. The same  Tune that runs perfect on dropping resistors ( stock injectors ) will turn Pig Rich on a vehicle with out dropping resistor. Using the recommended TS settings for PWCL. 

There is little information on how to properly tune PWCL.  Nothing on the MSextra and TS sites worthwhile that I can find. And of course it's all about finding that sweet spot for the PWCL settings. However, I did find an older article in the Mega Manul archives that explains how to  actually adjust the settings and what should happen. I'll post up this up a little  later. Right now I'm up to my neck in Alligators.

 

One of the interesting things in the article is how DT settings are affected by PWCL. I always knew this was probably affected and PWCL requires less DT than dropping resistors. This article explains how much you have to change ( decrease ) the DT settings. compared to using resistors. 

 

 

Edited October 12, 2017 by Chickenman

[Chickenman]

Here is one of the articles I found In Mega Manual to Tune PWCL :

http://www.megamanual.com/ms2/tune.htm

 

Quote

Setting the PWM Criteria

To tune the PWM [pulse width modulation] values for your engine, you need to know what kind of injectors you have: low impedance or high impedance.

• If you are running high-impedance injectors (greater than 10 Ohms), then set the:
  • PWM Time Threshold to 25.4 msec, and the
  • PWM Current Limit (%) to 100%.
  In essence you are disabling the PWM mode. This allows full voltage to the injectors throughout the pulse widths.
• For low-impedance injectors (less than 3 Ohms), you need to limit the current to avoid over heating the injectors. To do this, there is a period of time that you apply full battery voltage [peak] current, then switch over to a lower current-averaged [hold] current, i.e. peak and hold. Alternatively, you can add resistors in series with the injectors. See the Injectors and Fuel Supply section of this manual for more details.

  To run low-impedance injectors with the PWM current limit mode, you need to set two parameters - the "PWM Current Limit (%)" and the "PWM Time Threshold (ms)" - both are on the “Constants” page. The current limit % is the percent duty cycle when the current limit is invoked. The time threshold is the amount of time from when the injector is first opened until the current limit is activated.

  1. Start with:
     • PWM Time Threshold = 1.0 millisecond, and
     • PWM Current Limit (%) =
       • 30% on a V3 or V3.57 main board (if you have the active flyback circuit installed), or any MicroSquirt®.
       • 30% on a V2.2 main board (if you have the separate flyback board installed).
       • 75% on a V2.2 main board (if you do not have the separate flyback board installed).
  2. Once you get your engine idling, then first adjust the PWM duty cycle down in 1% increments until you notice a change in idle quality (be sure to hit the "send to ECU" button each time you change the value). This is the point where the current limit is too much and the injectors are not being held fully open.
  3. Then move the value back up 3 - 5% (for example, if the idle falters at 45%, then put in a number of 48% to 50%).
  4. Move on to adjusting the time threshold. Lower the time threshold by 0.1 milliseconds at a time until the idle quality deteriorates.
  5. Then increase it 0.3 ms.
  6. Now, repeat these steps (starting at #2). Adjust the duty cycle and time threshold alternately to get the optimum values for your set-up. You will converge on a set of numbers that work well for your set-up.

The injector opening time and PWM time threshold should be set to approximately the same value. So adjust the PWM time threshold, and the opening time together. However, once you start to tune the 'fine tune' the idle, if you have to revisit the PWM parameters, change only the PWM time threshold, but do not change the opening time.

The reason for this is that changing the opening time also changes the AFR, especially at low rpms, so it forces you to also retune the VE table. So unless they get to be different by more than about 0.5 milliseconds, leave the opening time alone after tuning the idle and cruise VEs (unless your are willing to retune those areas).

On the car, setting the PWM parameters is very easy to do and only takes a few minutes. At idle the overall injector pulse widths are small compared to their close time, so this will allow you to adjust the values. In other words, adjust the PWM current limit before taking the car out on the street where injector pulse widths become high, increasing the possibility of overheating your injectors (and blowing fuses).

You may find that you can idle at a very low PWM%, but the engine will stumble or cough if given any throttle. This can be due to a too low PWM% especially if your injectors are large and the idle pulse width is approximately equal to the PWM Time Threshold. In that case you may be idling almost entirely on the PWM Time Threshold. So rev the engine occasionally as you are tuning the PWM parameters, to ensure that you haven't gone too low.

Also, for some setups, an initial PWM Current Limit of 30% may be too low on a V3 main board (75% on a V2.2 main board without the flyback board), so they will need to increase this value - same for the time threshold. Use PWM time threshold values greater than about 1.5 to 1.7 milliseconds only with great caution – it is possible to burn out your injectors!

Note that if you are running the active flyback circuit and need PWM% of 40% or more to run properly (or 80% on a V2.2 with the standard flyback circuit but without the flyback board), your flyback circuit isn't working properly! Troubleshoot that circuit carefully to find out why.

 

Edited October 12, 2017 by Chickenman

[Chickenman]

Still have to find the article that shows the changes in DT between using Resistors and using PWCL. It's about .1ms to .2ms less than resistors if I recall correctly.

[turbogrill]

Hi,

I am using Supra 7GME hi-z injectors that I drive directly from microsquirt, seems to work well.

I bought the M445 cam from a Canadian

I haven't seen any dyno plots from the cam on a L28 (only on l20) so I cam curious about it.

 

 

[Chickenman]

If you can find a Dyno Plot on a Colt Cams C542S, that is  the exact same grind as the M445.  Very good grind, easy on the valve train.. 

When Shadbolt was sold years ago to an off shore company that was only interested in doing Industrial grinds, Geoff Bardahl ( who worked at ShadBolt ) stated his own company  Colt Cams and and continued with the performance grinds. 

Datsun L-series C542  =   224 degrees at .050", 280 advertised duration, .510" valve lift and 108 LSA.

http://www.coltcams.com/html/camshaft/index.cfm