Is GAIR/MAT Correction factored into VEAL?

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Is GAIR/MAT Correction factored into VEAL?

Postby robd » Thu May 24, 2012 4:02 pm

Sorry if this has been covered already and I may have already missed the answer, but when using VEAL is the MAT Correction factored into how VEAL calculates the VE table? So if say I was tuning at 20C and GAIR was at 102%, then I was tuning at 40C and GAIR was at say 99%, would VEAL give me the same VE values at both temps or would they be different?

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Thu May 24, 2012 5:45 pm

It would if the 99% and 102% are correct for the temperature, if they are not, then you will get slightly different VE numbers. Which could be an indicator of that.
However, also watch for heat soak on the MAT sensor. Then for at least a period, your temp sensor will read higher than real and the Gair correction will not be accurate, and can not be.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby robd » Fri May 25, 2012 1:58 am

Thanks for the reply, so is it recommended to leave the MAT Correction at 0's then to be accurate? I was finding that with 100% MAT value and 0's in the table GAIR seemed to be too harsh and my fuelling was going super rich or super lean!

So if my MAT Correction was spot on, and the air at the sensor was the same as the air entering the engine(it should be with current location), then should it not matter what temps I use VEAL at, as the VE table will always end up the same as the MAT Correction will correct for the difference in temp? So at 20C my idle was say at 14.7 AFR, at 40C it should end up the same?

I've currently got the MAT value at 50% and this is my MAT Correction Table(pinched from GSLenders msq)..
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Fri May 25, 2012 5:27 am

Typically, should follow the standard ideal gas law and I would recommend leaving it to the default settings during initial tuning.
if you have a reason to believe your GAir needs special correction, then you are better off applying the improvements.

In VE Analyze GAir cancels out and it is assumed to be working correctly as there is no visibility into what factors might be making it inaccurate.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby Twistedmetal » Fri May 25, 2012 6:57 am

Is there going to be a Gair analyze feature in TS/MLV in the future to help minimize Gair movement in the future?
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Fri May 25, 2012 7:24 am

How would you see that working?
You would need to assume all other corrections and your VE table are correct, then capture data at various IAT's.
There would likely be a good deal of room for error.
And typically it seems when the default Gair correction doesn't work properly, I find that the deviation is not consistent. It is related to other conditions such as heat soak on the IAT sensor.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby robd » Fri May 25, 2012 8:40 am

LT401Vette wrote:How would you see that working?
You would need to assume all other corrections and your VE table are correct, then capture data at various IAT's.
There would likely be a good deal of room for error.
And typically it seems when the default Gair correction doesn't work properly, I find that the deviation is not consistent. It is related to other conditions such as heat soak on the IAT sensor.

I'm assuming this must be what's happening to me then, heat soak on the IAT sensor. I've tried tuning with VEAL with MAT Correction all left at 0's, but as soon as my temps are then different, VEAL then starts to adjust my VE table and I just end up going around in circles!

When you say "In VE Analyze GAir cancels out and it is assumed to be working correctly as there is no visibility into what factors might be making it inaccurate." Do you mean just the VE Analyse in Megalogviewer or VE Analyse Live within Tunerstudio? I've just been using VE Analyse Live, and either I've got another issue or it's adjusting my VE table on top of the MAT Correction, so if say GAIR is at 99% and it's leaning off, VEAL then makes it richer, but then when my temps are different and GAIR is say at 100%, my VE is then too rich so then it leans it out!

At the moment I'm just trying to get solid AFR's so I know where I'm starting from, then if MAT Correction needs adjusting I can adjust it. My understanding was that even with the MAT Correction my AFR should still end up the same?! Sorry if I'm going off topic, but this part of the tuning is spinning me around in circles at the moment and I'm not sure if it's VEAL that's just going wrong or the MAT Correction/IAT temps! :(
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby jsmcortina » Fri May 25, 2012 8:47 am

Try to tune at one temperature, then you can arrive at a good VE table. Then if things behave differently at a different temperature you can experiment changing the air density correction.

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby robd » Fri May 25, 2012 9:09 am

Thanks for the reply James, yeah I've tried that, like today went out for an hour in my lunch break, started tuning when temps had settled at about 46C, but then they still change a few C either way depending on speed and even this change seems to alter GAIR depending on where it is and then affect VEAL adjustments to my VE. Plus if say I stop at a set of lights, my temps were going up to say 50C, so again VEAL adjusts my idle VE etc etc.

So I'm finding it very difficult to tune at one set temp at the moment. :(
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Fri May 25, 2012 9:11 am

Both VE Analyze in MLV and TS.

Heat soak is something that I have run across quite a few times. it is largely driven by sensor placement and type. If you have a metal IAT sensor that is placed so doesn't get much flow through it especially at light loads, it is more susceptible.
As an example, my own car at some point of development, with cowl induction so a short path to fresh air. The MAT sensor was in the bottom of the air box.
If I hopped in cold and ran VE Analyze, drive for 10 minutes to the grocery store. By the time I'm there the VE table was pretty well dialed in, the AFR's were right near target and with the southern ambient temps the MAT was reading 95.
Leave it in the parking lot while I shop for 10-15 minutes with the sun and the under hood temperatures, by the time I came out of the grocery store and fire it up, the AFR would be 1-2 points higher and cracking 17 when I blip the throttle and ego enrich hasn't had time to react. Check the MAT and it would be reading 120+. As I would drive down the road, it would get back down to within about 5 degrees of the 95, but that would take several miles of driving. During this period if ego correction is active it will be richening to compensate for the Gair leaning, Naturally if you are running VE Analyze during this period it will richen the table.

In a case like this, you can not really compensate for the Gair correction because it wasn't the Gair correction that was wrong, it was the temperature sensor reading Gair is basing it's correction on. You can adjust the MAT correction to try to compensate, BUT what would you do, set it to not lean any more over 100 degrees, so what happens on a cool day with the same scenario but 30 degree lower temps? Now adjust it to not lean any more over 70 degrees? But what happens when that 95 degree day comes back.

The real fix is to make sure your sensor is giving proper input. The easiest way is to look at a log after you "leave the grocery store", see if your MAT is reading significantly higher than when you arrived and taking too long to come down. If so, try to come up with a better location for your MAT sensor.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby HidRo » Fri May 25, 2012 4:02 pm

Phill, isn't the out of the box MAT correction values all 0's??
I've just opened the MSQ that comes with 3.2.1 firmware, and it's all set to 0's.
Should we just leave it at that?

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby M30guy » Fri May 25, 2012 4:37 pm

I feel that almost everybody using MS has some sort of heat soak making it too lean. :lol:
Sometimes, if the wait is long, my afr goes from 13afr to 15afr just idling at a drive-thru.

Re-starts is ok though you can just use afterstart enrichment.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Fri May 25, 2012 5:25 pm

HidRo wrote:Phill, isn't the out of the box MAT correction values all 0's??
I've just opened the MSQ that comes with 3.2.1 firmware, and it's all set to 0's.
Should we just leave it at that?

Thanks
Gonçalo


That is really for one of the firmware guys to answer really, but my understanding is that it is all 0's. This curve is to apply additional corrextion to the built in one base on the ideal gas law.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby pit_celica » Fri May 25, 2012 6:57 pm

You could add a custom filter in VEAL to stop modifying the VE table if the MAT is under a certain value or over a certain value. By example, create a custom filter by pressing "Custom Filter : OFF" button in the VEAL page. Enter a filter like this : (mat>46) && (mat<50)

Phil can correct my filter spelling if it's wrong, but you get the idea.

You can set VEAL to do not tune the cell under a certain RPM value, so your idle cell could stay untouched.

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby LT401Vette » Fri May 25, 2012 8:59 pm

Sam, that is a good idea.

But I think the formula should be the other way around.

(mat<46) || (mat>50)

It often feels like if the expression is true, the data is used, but if the expression is true, the data gets filtered.
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby pit_celica » Sat May 26, 2012 5:40 am

Ha ok, I get it now, thanks for the clarification.

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby robd » Sat May 26, 2012 12:30 pm

Thanks very much for the replies, I think I'll try the filters and check my logs before and after and see what's going on with the IAT sensor.

One quick question, with GAIR at 100%, that means MAT Correction isn't doing anything yeah? But does it also mean the ideal gas law isn't doing anything either, as the MAT Correction is a correction on top of this law does the law still apply even with GAIR at 100%?

Knowing the answer to that would help me understand further what's going on with my VE table and VEAL, as for a lot of those temps with my current MAT Correction GAIR is at 100% for quite a lot of the tuning. So if that means neither the law or MAT Correction is altering my VE, then maybe my issue is elsewhere!

Thanks in advance. :)
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby pit_celica » Sat May 26, 2012 1:28 pm

In MS, the temperature of reference for the MAT correction function is 70°F. At this temp, Gair will be at 100%. If at any other air intake temp Gair is still at 100% (because you are using a non-linear MAT correction curve by example), this means that the air density factor is disabled from the fuel equation.

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Re: Is GAIR/MAT Correction factored into VEAL?

Postby robd » Sat May 26, 2012 4:19 pm

pit_celica wrote:In MS, the temperature of reference for the MAT correction function is 70°F. At this temp, Gair will be at 100%. If at any other air intake temp Gair is still at 100% (because you are using a non-linear MAT correction curve by example), this means that the air density factor is disabled from the fuel equation.

Sam

Thanks very much, that clears that up then. Could I add a filter for GAIR in VEAL and VE Analyse? So filter it so anything below 100% and over 100% would be ignored and it wouldn't modify the VE table at that time? Maybe that way on a longer drive where temps were changing a lot, I could then try and minimise the effect and just tune it where temps are similar and GAIR is at 100%.

Cheers :)

Oh and I went out in the car earlier to pick up some grub and logged my runs. It's been a hot day here today with temps of about 27C in the day, I went out earlier tonight and MAT temp before I started the car was 23C, MAT temps when I stopped after about 10 mins driving around town were 42.7C, spent about 5 mins in shop, came out and MAT temp was 46.7C, after 5 mins driving temps dropped back down to 42.7C. Would you say that sounds like heat soak or ok?
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Re: Is GAIR/MAT Correction factored into VEAL?

Postby pit_celica » Sat May 26, 2012 4:33 pm

The problem with adding a filter for Gair is that you need your MAT to be at around 70°F to get something to log. According to the number you are giving me, you are in the 40-45°C while running (104-113°F).

Instead, I suggest adding a filter to MAT as specified above. The goal with all of this is tuning the VE table. To do it, you need to remove the more variable you can. Keeping MAT constant will remove at least a variable. If MAT is constant, Gair won't vary. Then, you will have a VE table perfectly tuned for this MAT temp. After, if your AFR vary with MAT, do not touch your VE table, only the MAT correction curve.

Remember what a VE table is, it's the shape of the Volumetric Efficiency of your engine relative to RPM and MAP. So, when tuning VE table, only RPM and MAP should vary, nothing else (in a perfect world). This is why you should only tune your VE table when your CLT is constant (warmed-up), when your MAT is relatively constant, when your TP isn't moving too fast between load change (this will be tuned after with accel enrichment).


For reference, my MAT temp are about 95-105°F on a 75°F day. My MAT is mounted in the plenum of the intake manifold.

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