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Discussion Starter · #1 ·
Hi guys, screwing around with tuner cat again...

I've got several different bin files stored on my computer, and looking at them, I see they all run incredibly rich.

Am I reading this right? There only seem to be 3 tables that affect A/F ratio:

--% change to AFR vs. RPM @ WOT
--% change to AFR vs. coolant temp @ WOT
--Open Loop AFR vs. coolant temp vs. MAP

Am I missing something here? Is there another table that trims these values back down?

Example: At 176* F, the open-loop AFR is 12.8

---Then: @ 5200 rpm: -6.6% and @ 176* F, +17.2%

So, the sum of percentages is +10.6%, which equates to an AFR of 11.5:1 @ WOT @ 5200rpm. cwm8




This is pretty much the same story with different tunes I've looked at, for different B-Bodies, at all RPMs.

I was under the impression that engines made best power around 12.9--13.1.

Am I overlooking something? At WOT we're only using open loop AFR table, right?

Maybe there is some more power on the table!


Thanks to anyone who can help!
 

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Discussion Starter · #3 ·
No, I'm poor right now:(.

But, what's got me wondering, is that the factory intends it to run that rich! Unless I'm missing something.

Looking at a couple of professional tunes, I see basically the same thing!

I'd love to have a wideband system, but I'm unemployed right now.
 

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The only table you should be looking at is % change to AFR vs. RPM @ WOT. This is the "power enrichement table" that is used once you're in closed loop.

You are incorrect about being in open loop at WOT. You are still in closed loop but the O2's are ignored. Therefore, the AFR in open loop table isn't used and your assumption about a 11.5 AFR is incorrect.

You really shouldn't be messing with the AFR unless you have a wide band to refer to. The stock O2's can be used with DataMaster but they aren't that accurate beyond stoich.
 

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...ok...lots of sketcy info in this thread and I'm sure I'm opening a BIG can of worms here...

You're right, thats what the tune is commanding...but if the ENTIRE SYSTEM isn't calibrated properly, then thats not the AFR that you're actually achieving.

In order to really tune the vehicle right (so that the AFR you command is the AFR you get, and so that the AFR you command is the AFR the engine wants), the entire PCM calibration needs to be re-touched. The LS1 tuning world has started catching on to this, but most of the LT1 world seems to be ignoring it.

Most LT1 tuners strap a car to a dyno, and just play with the + and - buttons in the % change to afr vs rpm at wot table until the wideband reads correctly...this works, but when the weather changes, the car isn't getting the same AFR at WOT anymore...it's usually close (thanks closed loop fuel injection) but it's not perfect...further calibration of everything (sensors, injectors, temperature correction tables and so on) prior to adjusting any of the full throttle tune, would make it not only mean the calculated "commanded AFR" would equal the actual AFR, but it would also make it able to do a better job achieving that actual AFR despite the day to day changes that an engine sees.
 

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Discussion Starter · #7 ·
Ok, I'm kinda with you here, I should've prefaced everything with : "I have the car set to run in open loop at all times."

Before I knew better, I installed a set of bosch O2 sensors, which are garbage, so I've set the tune so that it never reaches closed loop.(and therefore ignores the erroneous signal that makes the car run sh1tty.) I haven't gotten around to installing a set of GM O2s... I had planned to use a dual-channel wideband with simulated narrow-band output to supply the PCM.

Cupcake, I was under the assumption that the DIFFERENCE between closed and open loop was either the use or ignorance of the O2s. I mean, when the PCM isn't using O2 feedback to control the injector pulse-width, then what table is it using? Isn't that the Open-loop AFR table?

I'm working off of a BH tune here, and evidenced by the black soot that accumulated on the bumper, it was incredibly rich. I leaned it out a bit, which helped, but it still doesn't pull like an 845 cammed car should.

I'm going further down the rabbit-hole. What should I do to re-touch the PCM, as you said Mike, can the average dyno-junkie accomplish this?
 

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Particularly with a car this heavy the perfect dyno tune is NOT good on the track but rather dangerous on the track. A good tuner can still use a dyno as a tool but he has to make changes after max power is found to keep it safe on the track.
 

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This should get you close

14.7/(1+PECool/100+PERPM/100)


IN the PE coolant table there is a value of 15.6 or 16 depending on TC or LT1Edit software. Plug that number into the formula and the number in your rpm table to get the AFR So... for an AFR at 6000 rpm you'd have this as the formula:

14.7/(1+ % change to fuel/air ratio vs rpm at wot/100 + % change to fuel/air ratio vs coolant temp at wot/100)=afr

14.7/(1+15.6/100+10.6/100) and the AFR should calculate out to 11.65

14.7/(1+.156+.106)=11.65 afr

14.7/(1.156+.106)=11.65 afr

14.7/1.262= 11.65 afr

Hope this helps you understand how tuners come up with those percentage numbers in the PE table
 

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Ok, I'm kinda with you here, I should've prefaced everything with : "I have the car set to run in open loop at all times."

Before I knew better, I installed a set of bosch O2 sensors, which are garbage, so I've set the tune so that it never reaches closed loop.(and therefore ignores the erroneous signal that makes the car run sh1tty.) I haven't gotten around to installing a set of GM O2s... I had planned to use a dual-channel wideband with simulated narrow-band output to supply the PCM.

Cupcake, I was under the assumption that the DIFFERENCE between closed and open loop was either the use or ignorance of the O2s. I mean, when the PCM isn't using O2 feedback to control the injector pulse-width, then what table is it using? Isn't that the Open-loop AFR table?

I'm working off of a BH tune here, and evidenced by the black soot that accumulated on the bumper, it was incredibly rich. I leaned it out a bit, which helped, but it still doesn't pull like an 845 cammed car should.

I'm going further down the rabbit-hole. What should I do to re-touch the PCM, as you said Mike, can the average dyno-junkie accomplish this?
Using a widebands simulated narrowband output all the time...is less accurate than letting closed loop work properly off of good narrowband O2 sensors (GM...or I've had GREAT luck with NTK's also).

You need to properly calibrate your part throttle tune first, and then you might need to make changes to higher airflow calibration (airflow that occurs in power enrichment mode) in the MAF or VE tables (VE if you're running without the MAF) until your commanded AFR is equivalent to your actual measured AFR...it takes time, and a lot of math (it's not just the MAF tables, there's all sorts of injector calibration, coolant temp stuff, and so on) to get it right. When thats done, you should REALLY re-enable closed loop to allow the car to correct for differences in fuel, atmoshpere, temperature and so on.

I'm sorry I'm being kinda vague. This is an incredibly in depth topic, and it just takes me forever to try to explain it thoroughly...I've spent years researching tuning, teaching myself to tune, learning from other tuners...and I'm just recently beginning to really be able to calibrate most of whats there for us in the GM PCM's...it's not difficult, but it is tedious.
 

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This should get you close

14.7/(1+PECool/100+PERPM/100)


IN the PE coolant table there is a value of 15.6 or 16 depending on TC or LT1Edit software. Plug that number into the formula and the number in your rpm table to get the AFR So... for an AFR at 6000 rpm you'd have this as the formula:

14.7/(1+ % change to fuel/air ratio vs rpm at wot/100 + % change to fuel/air ratio vs coolant temp at wot/100)=afr

14.7/(1+15.6/100+10.6/100) and the AFR should calculate out to 11.65

14.7/(1+.156+.106)=11.65 afr

14.7/(1.156+.106)=11.65 afr

14.7/1.262= 11.65 afr

Hope this helps you understand how tuners come up with those percentage numbers in the PE table
but my point is, like I said...yes that absolutely IS how you get the commanded AFR...but is it actually the measured AFR in the tailpipe? usually it's not, calibration of the injectors and MAF sensor and so on really really come into play for that
 

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Particularly with a car this heavy the perfect dyno tune is NOT good on the track but rather dangerous on the track. A good tuner can still use a dyno as a tool but he has to make changes after max power is found to keep it safe on the track.
on a ****ty dyno with lightweight drums yes...on a nice dyno that allows a real load on the engine (such as a mustang dyno, or dyno dynamics) the dyno tune will be pretty dam good...it really has nothing to do with the weight of the car so much as making sure a pull on a dyno is realistic...an engine makes heat while it pulls (5th gear results in more heat than 3rd because aerodynamic drag makes it take longer to pull through at full throttle)...so if the cooling system isn't taking away enough of that heat from the chambers, a longer pull will require the tuner to run a little less spark, or a little more fuel or something of that nature due to heat soak
 

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On an eddycurrent dyno you still need an operator to set it up right to load the engine enough.
The more I learn the less trusting I am of most others.
 

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Dispell Myth

and

Look for Truth

!!Rate of acceleration at the track
!!Rate of acceleration on the dyno
Match them and you will have a valid dyno session.

!!Duration of 1/4 mile
!!Duration of dyno run
Match them and you will have a valid dyno session.
If duration of the run has an effect on the AFR the fuel system/delivery is sub par
 

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Come on guys,

WideBand in the car!
 

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Tad, you're absolutely right...the only benefit I see to a lengthy dyno pull (ie equal to how the car really accelerates) is to know wether or not the car is going to knock as the chambers heat up...the AFR should be correct anyways, or else again, you're right, the fuel system is to blame.

As for a wideband in the car...yes and no. Mine goes in when I'm tuning, and it comes out when I'm not tuning. I DO NOT run off simulated narrowband from a wideband...think of the tremendous resolution a narrowband sensor has right around lambda 1 versus the lower resolution that a wideband has around lambda 1. Closed loop targets lambda 1...difference in gas from day to day, pump to pump, as well as the atmosphere you're driving the car in...are corrected for MUCH BETTER in that range that the narrowband can measure and fuel trims can correct for...and 99 times out of 100, that fuel trim correction with the narrowband, is perfect for all the resulting offset fueling that PE and other open loop fueling see's...meanwhile when it's 1-2% difference, the wideband thats simulating narrowband, probably won't register a difference, and thus closed loop won't correct for it...1-2% at full throttle in a street car...probably no big deal at all...but 1-2% in my MPG and thus wallet...is important to me.
 

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Discussion Starter · #20 ·
That's a good piece of reasoning, right there. Is the output range of a wideband still only 0-1 volt? If so, the resolution is indeed much lower.

I've heard that recently, the industry has been working on running even leaner than stoich at the very low load areas with some of the new cars, like in the neighborhood of 16:1!
 
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