A/F Tuning...

[CDX_NSX]

My S/C setup is currently assisted by a S-AFC to control the A/F ratio. As it is right now, it is setup at around 14.5 at cruise, and ~11.5-12.5 at WOT.

I'm considering moving up to an AEM EMS, but was wondering about the proper A/F ratio tuning.

In this thread, a similar idea regarding the handling of the A/F ratio is mentioned in the first post by torquefreaks.com.

However, looking at this thread which has results from a tuning by Autowave, the A/F ratio is pretty much a constant high 11 to low 12 across the RPM range.

I'm in Southern California, and was considering having Autowave tune the AEM unit for me, but seeing the A/F plot in the second linked thread, I'm not sure if it is the ideal setting for my street driven car.

I'd appreciate any relevant input that you can provide. Thanks!

 

[kouasupra]

11.5 to 12.0 A/F for the street is what I recommend it's better to be running a little richer then leaner. I also recommend you buy a wideband to monitor your A/F reading because during the nights the car will tend to run a little leaner, because of the air density. While the A/F will be richer during the days. Just my .02 cent!


Koua

 

[CDX_NSX]

Thanks! I do actually have a wideband. Wouldn't a 11.5 to 12 constant A/F basically be just burning fuel at RPMs that don't see boost?

 

[CDX_NSX]

OK. I did a little more reading. Is it true that an Dynoed A/F chart only represents the A/F reading at WOT and not in stages between?

 

[KGP]

Dynos typically show AF under WOT load.

 

[CDX_NSX]

OK. Thanks!

 

[true]

Is it true that an Dynoed A/F chart only represents the A/F reading at WOT and not in stages between?

It depends on what kind of dyno you are using. An Inertial dyno(your typical DynoJet) is really only useful for an A/F at wide open throttle, like KGP said. It is unfortunate as, in my opinion, the absolute most important thing about any properly tuned FI vehicle is cruise condition. You will simply never get an 'OEM' feeling/running car that has a dead-nuts A/F off boost tuning specifically with a Dynojet. It's REALLY easy to get a good A/F under WOT, but much more of a challenge to get the OEM feel at any throttle angle. There are boatloads of FI cars running around with decent A/F curves under boost/WOT -- but also running rich/smelling of gas/running lean/sputtering at low throttle conditions.

 

[DDozier]

It depends on what kind of dyno you are using. An Inertial dyno(your typical DynoJet) is really only useful for an A/F at wide open throttle,

I do not understand this statement, if you want to tune for partial throttle conditions, then strap the car on the dyno and do not push the throttle wide open, with the use of the variable load brake on the dyno you should be able to tune for almost any load, RPM, and throttle possition. Then fine tune your map on the street. If I am missing something please explain, but I sure hope we made the right choice when picking dyno for the shop.

Dave

 

[kouasupra]

14.6 A/F is cruising speed. The A/F is at that because of emission laws, not to mention it's good for the gas. 14.6 A/F is fine because your not at full throttle or at least 80% throttle. Once you give about 80% or more throttle the fuel piggyback as such; super afc, or etc will take effect to bring your A/F to whatever A/F you have it set to. I don't know about the nsx ecu, it might have a open and close loop. Open loop, meaning you can tune the A/F at certain rpm up, and close loop means you can't tune it at certain rpm. If you try to tune it at close loop the ecu will override the piggyback system and cause it to run leaner or richer depending on what the ecu see done to the map ecu. I hope this makes sense..LOL..my .02 cent


Koua

 

[DDozier]

OK. I did a little more reading. Is it true that an Dynoed A/F chart only represents the A/F reading at WOT and not in stages between?

A dyno is simply another tool for a tuner to use, some see it only as a way to measure HP & TQ and AFR, under this application you are looking at peak information only, peak HP,TQ & AFR charted over a engines RPM range, but a dyno can be used for much more than just peak information, you can log all the above information and more over time, meaning you can put the car on the dyno and simulate several stop and go runs or diving condition that are causing problems with your real world tune (partial throttle conditions), then review the data charted over time. You can change the load using the variable brake on the dyno and then simulate different load conditions like going up hill, by simply unloading the drum brake and going to zero throttle input you can simulate down hill as the drum continues to push the tires due to its mass. There are a few things you cannot simulate with a dyno and one of them is aerodynamics and the effect it has on the car, as well as chassis dynamics and traction issues, as these are altered when the car is strapped into position

I have only just started playing with this tool and fortunately I have a very good teacher to learn from, but a dyno like any other tool in a tuner’s tool box is only as good as the tuner’s knowledge of how to use that tool.

I am getting off the soap box now.

Dave

 

[KGP]

First, I need to clarify my earlier statement. When I said Dyno's typicaly reflect AF under WOT, I should have been more specific. My meaning was that the dyno sheets you find posted on this, or most any other forum, are almost always of WOT conditions.

Dave, as it might relate to True's statement - When I was making a dyno appointment with the local guys last summer, who have both a Dynojet and a Dynapak, he asked if we would be doing any constant state tuning. If "yes," he reccomended the Dynapak for that purpose. Don't ask me why, because I really don't remember, other than him saying the Dynapak was better for constant state, i.e., crusie conditions, tuning.

 

[CDX_NSX]

Thanks for the info, fellas. Indeed, the value of the dyno is measured by the competence of the tuner. I'll give autowave a call to discuss further their method of tuning. I understand that many speak highly of their capabilities, and now better understand the values of the posted A/F plots.

If anyone has had experience with Autowave's AEM tuning, it would be great if you could let me know the A/F ratio parameters that were set.

Thanks again.

 

[true]

Dave, a standard Inertial dyno does NOT have a variable load brake. It is near impossible to properly tune a partial throttle vehicle on the likes of a DynoJet Dyno, without one of their custom accessories. DynoJet has recently released a LoadPack, but I have not yet heard any feedback, and do not know any DynoJet owners that are interested in getting one. If I remember correctly, the DynoJet load pack uses air-pressure for its braking, vs. the standard water or electronic type eddy-current standard loading type dynos. I am not sure if you may have or be familiar with this option, (would love to hear feedback if you have used it) but is only available for one of their Dyno models. If you are not familiar, an Inertial DynoJet without accessory does _not_ have a variable load brake, and cannot 'hold' an RPM point for tuning specific cells. Another tuning tool that I have never seen an Inertial dyno possess is a 5 exhaust gas analyzer. I know that both Mustang and Dynapack both have the ability to use a 5 exhaust gas analyzer, which is useful for tuning ignition timing. (Cannot use a 4 wire standard wideband o2 for this).

In my opinion, it doesn't make much sense to convert an Inertial Dyno in this way. The very experienced tuners I know who want a tried and true method of fully loadable tuning are using DynaPack or Mustang dynamometers.

As far as business goes, everyone and their brother know about the 'Dynojet 248c' and customers are generally interested in seeing the most horsepower. This dyno is right up their alley is it will graph 'more' HP than a comparable eddy-current type loading dyno, for example. What might be best for getting a perfect tune, may not be in the best interest for a business who is targetting high use of non-tune dynos. (people wanting to see how much peak HP an intake or exhaust gives at 7K rpm.. ) For most of the shops with DynoJet dynos, the best use will be to view HP and tune A/F at WOT. It can't really be used for tuning much else. Hope this helps.

By the way, what dyno did you choose, and assuming it was a DynoJet, did you also go with the Loadpack conversion option?

EDIT: To reference KGP's last post, braking type dyno's in fact do allow pure steady state tuning. For example, dyno brake is applied that will 'keep' the car at 1250 RPM.

On an intertial Dyno, this is impossible. Can you imagine trying to target a fuel cell located at 200mBar @ 1250 RPM? The car passes that cell so quickly even with barely any throttle a standard Dynojet will never be able to reliably give the operator a valid result when taking less than a second to spin up to 1500 RPM. Do it 10 times and you'll likely glimpse 10 different readings. Trying to apply a correction would just be guessing. That is the key of loading type dynos, the dyno itself can hold 1250 RPM until you have nailed down specifically whatever A/F you want to run.

I do not understand this statement, if you want to tune for partial throttle conditions, then strap the car on the dyno and do not push the throttle wide open, with the use of the variable load brake on the dyno you should be able to tune for almost any load, RPM, and throttle possition. Then fine tune your map on the street. If I am missing something please explain, but I sure hope we made the right choice when picking dyno for the shop.

Dave

 

[DDozier]

By the way, what dyno did you choose, and assuming it was a DynoJet, did you also go with the Loadpack conversion option?

Dynajet 248X with Dynotrac Load Control and WinPep7 software, yes the brake is actuated by air.

I have not tried to hold RPM's at anything under 2000 RPM but I will have to give it a try.

Dave

 

[sjs]

14.6 A/F is cruising speed. The A/F is at that because of emission laws, not to mention it's good for the gas. 14.6 A/F is fine because your not at full throttle or at least 80% throttle. Once you give about 80% or more throttle the fuel piggyback as such; super afc, or etc will take effect to bring your A/F to whatever A/F you have it set to. I don't know about the nsx ecu, it might have a open and close loop. Open loop, meaning you can tune the A/F at certain rpm up, and close loop means you can't tune it at certain rpm. If you try to tune it at close loop the ecu will override the piggyback system and cause it to run leaner or richer depending on what the ecu see done to the map ecu. I hope this makes sense..LOL..my .02 cent


Koua

Throttle position is not the critical factor, nor is RPM alone. You can blow the engine to smithereens at way under 80% throttle and low RPM when running boost, especially on a turbo car. Yes of course the NSX uses closed-loop like every other modern car, which is why they have O2 sensors. It operates through a certain portion of the load vs. RPM map before switching to fixed maps + trims, again like all recent cars.

 

[sjs]

It sounds like Dave has access to the latest offerings from Dynajet. I’ll be interested to hear more about it. But let’s not give the impression that dynos without a variable load brake are useless other than at WOT. Although you can’t hold it at a specific load & RPM to tune a particular cell, you can do a variety of part-throttle pulls to record a broader range of the maps than you get with the typical WOT pull. That’s especially important on turbos that use far more of the map than do NA and SC engines.