IAT % Variance

Steve 00RT/10

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I am having some trouble dialing in the IAT function for a one card fits all scenario. Does anyone have experience with this? What percent variances is anyone using? I'm finding that 10-15% each way may be end up being the target. I started at 4% each way.

The percent difference fuel pulse on my separately tuned temp cards from last year ranges from 19% to 48% across the RPM range from a outside temp of 50 to mid 90s. It is definitely not a one percentage fits all RPM segments.

thanks--Steve
 
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DAMN YANKEE

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Folks, Steve is raising a great question and one that all the VEC3 and newer model owners will have to contend with. But to bring everybody along, allow me to give a little background on Steve's question..

IAT = Intake Air Temperature, and as many of us know already, when the temperature of your intake goes up...the air inside expands. If your air expands and your fuel remains the same...you end up with an overly RICH mixture. That means too much fuel being added to too little air. As you might imagine...in cold temps, the air compresses and, therefor there is more of it...keep adding the same amount of fuel and, yep, too much air and not enough fuel...a LEAN mixture or one without enough fuel is created.

The VEC3 has a new software screen added to it. Its a new and important one and sue beats having no ability to account for temp changes. It looks like this.
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This new program allows us to potentially add one last adjustment before the final calculations that drive the fuel calc signal is sent to the injectors. Simply put, this is a temperature scale, one that allows for more or less injector seconds to be added based on the IAT (Intake Air Temperature).

Now Steve's logs show a real requirement to find a way to properly account for the differences in air temperature as his car is driven in everything from pretty much freezing temps to over 100 degrees. He knows that his car's wideband logs are showing and Air-To-Fuel (Lambda...in his supercharger is approximately 11.7-11.9) that is way too lean as he ran his car in colder temps.

The details are as follows:

On May 22, 2007, Steve took his car out when the outside temp was 76 and the intake was running at a pretty constant 96 degrees. In other words his IAT was...96 degrees.
He did his run and found that his A/F was running fairly flat at about 11.5..not too bad. But he wants the target 11.9, so he slightly reconfigured his VEC3 fuel tables.

On June 8th, 2007, out goes Steve again for some logs. The outside temps were cooler coming in around low 60s with his AIT reading a lower 68-82. His log showed that his air/fuel was now too LEAN...way too lean, just what one might expect. But his numbers required some real attention.

Excellent at 96 IAT....too lean at 80 IAT...So now the question being asked is have any of us worked with the IAT tables to see if we can get it to properly alter the fuel pulse to compensate for the temperature changes in the intake..

Steve,

1. The temperature range of the VEC3's sensor is very precise and encompasses a temperature range that the engine will never actually see. Sean told me this and when I realized this, I tried a number of different things. You have already mentioned that " I'm finding that 10-15% each way may be end up being the target. I started at 4% each way" "

So that everybody is with us, that would result in a VEC3 table that looks like this.

A 4% each way table would look like this

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A 12% each way table would look like this

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When I realized that the scale of temperature ranges was far greater than my car would see I decided to change the slope of the curve by bringing in the sides...

Now, I still working on this because here in CT we havent had great temperature changes yet. but this is what I am currently experimenting with...

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Have you tried changing the slope so it creates a much greater reaction? I need some really hot temps out here to be sure. I still havent got the table to 86 degrees yet because, so far, the A/F numbers (in my limited temp range) are still looking good with no peaks above 12.4 on a warmer day. Steve, it doesn't get colder here now!

I have not shared any of this with Sean yet, so take it with a grain of salt. IN OTHER WORDS, PROCEED WITH CAUTION AND DO LOW RPM LOGGING. I literally drive around with my best card and have some new IAT cards that I run just long enough to log at this point.

Hope that helps!!
 
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Steve 00RT/10

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Because it appears to have been bogus readings for the bad logs the other night......either a software glitch, or user error.....I will have to wait for a cool day to try again. I ran the same card again yesterday with excellent results at 80 degree outside temp. (IAT 90). Today, at 90 degrees outside (IAT from 110-119), I was running way too rich on the first log. I was set at +5.3 -6.3

I have tried various combos of +/-. You're exactly right above......all equal percents in and out will cross at 100 degrees IAT. The way it's supposed to work is that you get a set of numbers (AFR) you're happy with---take the mean IAT in your log from those runs......and use that as your crossing line.

I'm having a hard time dialing that in. The reason I would try 12 each way is that if my logs the other night at 66 degrees outside were running lean at all--which I'll never know.....I would want fuel going in faster below 100. My line was crossing around 90 degrees IAT. By going to a large amount, I ought to see some change if it's working properly

Dan, I believe you're using the same sensor I am......the car's IAT sensor at the airbox.

Steve
 
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DAMN YANKEE

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Yes, that is correct...airbox.

Let us know what happens. Ill do the same when it heats up here...right now its 73....
 
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DAMN YANKEE

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Steve just sent me the new numbers using the "higher slope" effect and they are looking good! He will be making a full report soon. Looks like we are making good progress on utlizing this important new panel.
 

Joseph Dell

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So a few things you need to know.

1 - if you use the 'resistor' trick from your old VEC2, then the IAT won't ever read over ~98.

2 - if your IAT is HOT (say 150+), your car may need less fuel to run, but it could really use MORE fuel to cool down the motor. Fuel has a cooling effect. In fact, a rich mixture runs cooler than a leaner one. So taking fuel out when the car is getting hot may NOT be a great idea.

3 - the BEST thing to do is to datalog what your IATs are and THEN formulate your IAT strategy. A ROE w/ a 12psi pulley + a D. Weaver pulley will run HOT all the time, for example...

my .02... but i rarely find this forum. too many clicks to get here...

JD
 
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Steve 00RT/10

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Good point Joseph. I'm a mere 5 pounder. I was using the extreme limits of the IAT parameter (10F-185F). The slight slope had basically no reaction at all. Dan told me he had some limits set, so I tried it. I am using 35 to 136. I have yet to see temps over 119. My logs are pretty much mid 11s--pretty safe. At least now there is a noticable difference when the temp goes up. I could lower the upper limit a tad next week. I want to play around a little more.

Right now....off to Gingerman. I can run the whole track in 4th gear so won't be working the engine real hard. I have some richer cards with me if needed.

Steve
 

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Steve just sent me the new numbers using the "higher slope" effect and they are looking good! He will be making a full report soon. Looks like we are making good progress on utlizing this important new panel.


I am looking forward to the results. I haven't had time to play with this cool new feature in the VEC3's.
 
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Steve 00RT/10

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I thought I was going to get a 'cool' log IAT correction today as the outside was 62. not to be.......the IAT was 73-77 on the 2 logs I did......similar to what I already did last week. As posted above, initial results using temp borders are promising. I am set at +8.4 / -9.4 with a temp range of 35 to 135F. Prior to setting this range, correction results were too minimal to measure and basically ineffective.

Running at the track last Friday..............around 90F, my AFR in 3rd and 4th was right at 11.3 to 11.85 or so. Right on the money. The sessions were quite decent for length, so I'm pretty sure my IAT was up there, yet the AFR looked pretty consistent when I looked at the meter under WOT on the straights.

I'll need a very cool day to see how my plus range is set.

I would ask the question of those much more versed in AFR / fuel cooling /detonation:
Is there a rule of thumb for letting the AFR go rich when the IAT gets to a certain point?
I would think every situation a little different with boosted cars. A 5 pound car with conservative spark tables would not be as at risk as a finely tuned big boost car. Until someone chimes in to the contrary, I'm leaving my upper limit at 136F

As for a 5 pound Roe car on the track.........my 4th gear pulled mostly harder (never less than) than all the stock Vipers in 3rd I ran across. I ran Gingerman mostly in 4th last year too. Keeps the RPMs way down--around 5K tops. Plenty of grunt in 4th gear to break loose at any corner on the track when unwinding.

Steve
 

Joseph Dell

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Were you running an old VEC2 previously? What i'm getting at is that there used to be a 'resistor' that you would add to the VEC2 wiring. if you still have that, it impacts the IAT readings.

just curious...

JD
 
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Steve 00RT/10

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No, I had my VEC2 upgraded to VEC3 capabilities by Sean. Not a VEC3, but able to perform the added IAT feature by tweaking the sensor settings after installing the program. I have to use the General Dataset ID108. New VEC3s don't use this setting. I have seen IATs of 119F so far.

Still curious what the upper limit could be safely set at to allow for the fuel cooling effect to come into play. We know the stock PCM is programmed to run richer in hot weather. I wonder where the break point is for the stock PCM?

Steve
 
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Steve 00RT/10

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Here's where I'm at with the VEC 3 IAT tuning feature and the new 1.7 RR addition to the car. When I first started logging, I kept the IAT temp parameters at the limits (10F-185F) and used 4% each way (as recommended) for a starting point. My log results became more than a little puzzling as the the slope of the line at these settings was so slight that it basically had no effect at all on fuel correction. I was quite skeptical about the new feature and always carried my old cards with me when traveling. During some communication with Dan a couple weeks ago, he mentioned that he had set some temp limits for his. A light bulb went on. Condensing the temp parameters creates a much steeper slope for fuel correction. I have now ended up with the temp limits set to 35F-126.1F and am at +12.4 / -11.8%. My line on the graph crosses about 83F......but in actuality (logging) the zero point is about 88F. I have decided to keep the limit at 126 to kind of do what the factory does---stop taking any more fuel out when it's that damn hot. Fuel has a cooling effect and the factory richens it up a little when it gets real hot for a safe guard. When it was 95+ here a few weeks ago, I saw 124 IAT on the log for one of the runs......this was before the settings noted above. I have now pretty well nailed down the AFR tune from 53F to 73F outside temps and IAT temps of 67-87 with the above settings. I think this will remain close on the increasing outside temp to about 95F, however my gut feeling is that I will top out at +15-20% and -15-20% before I'm done. If this ends up to be the case, it would close to the variation in the 3 temp cards I ran last year. Roughly a 40% swing from the coldest to the hottest. Unless there is an aberrant log run from my current settings (and I'm back to ground zero), I think my actual fuel tuning is about done and I will only be playing with the IAT +/- fuel parameters from here on. I need hotter and colder weather to experiment more. I am tuned at roughly 11.5-11.8 AFR. I should also mention that I have not monkeyed with any spark values from Sean's original card.

On another note: For the first time, I tried some 2nd gear logs and found that the log showed a little lean through some of the range even though my 3rd gear log with the same card and IAT was spot on. Per Sean, the higher the gear, the quicker the revs, the more chance of a little aberration. He says to log in 3rd or 4th. I will stick with 3rd. 4th is easy enough to see on the inside meter as the revs are much slower. I also did a little research on line which stated the same as I just noted and the article also said to log in 3rd or 4th.

A final thought on the new IAT fuel correcting feature as I see it:

Unlike a Paxton, which is sensing supercharged air temps at the intake and the computer is adjusting fuel correction based on the actual intake air temp, we are using IAT temps from the airbox prior to entering the SC. This is not accurate enough for fuel correction without logging to see the AFR and plotting your corrections from the results. If you log and enter correction factors to support your desired AFR, then the IAT numbers we use for this calibration / correction become much more accurate because, although it is not the actual intake air charge temp..........it becomes a relative number (based on AFR log results) and has a definite correlation to the actual air charge temp coming out of our blowers into the engine. I don't think it can ever be as accurate as the Paxton IAT sensing /correction method being that we can only ever plot a linear line no matter the parameters inputted.......but it is much better than we had. I think and hope I have now found the sweet spot for my AFR and will now continue to play with the percent correction factor as weather permits.

Steve
 

dun4791

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I have a couple of questions.

Why is there not an IAT sensor after the S/C? The temp difference could be very great without an aftercooler.

Doesnt this VEC3 start to pull timing at a set IAT parameter? I wouldnt worry so much about richening it up at say temps over 150 as I would to start pulling timing progressively starting around 140 or so.

Isnt max timimg 32*?

Is the VEC3 just manipulating the global fuel tables? Or is there a tuning capability based on the MAF voltage readings?

I would log in 4th gear on these cars as the load will be greater and will require more fuel.

Sorry about the questions, I trying to get a handle on which S/C Im going to install on my car, and the tuning is a major part of my decision.
 
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Steve 00RT/10

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I have a couple of questions.

Why is there not an IAT sensor after the S/C? The temp difference could be very great without an aftercooler.

Doesnt this VEC3 start to pull timing at a set IAT parameter? I wouldnt worry so much about richening it up at say temps over 150 as I would to start pulling timing progressively starting around 140 or so.

Isnt max timimg 32*?

Is the VEC3 just manipulating the global fuel tables? Or is there a tuning capability based on the MAF voltage readings?

I would log in 4th gear on these cars as the load will be greater and will require more fuel.

Sorry about the questions, I trying to get a handle on which S/C Im going to install on my car, and the tuning is a major part of my decision.

I am not the guy to go into depth on the spark part. I have chosen to use the spark curves Sean sent me initially with the purchase. Basically 6 degree retard at 5 pounds of boost with 93 octane gas. I have no water **** for cooling and a cast piston car. I don't really care about squeezing a few extra HP out of it. My 5 pounder runs quite strong enough for me the way it is. ( I toasted another 'sport bike' Friday night from 60-125, after being provoked of course ;) I have done extensive AFR tuning with the VEC. My VEC is an upgraded VEC 2 -- not quite the same as the VEC 3. I have only the old VEC 2 instructions.

That being said---as I understand it: the stock PCM controls the car in all closed loop operation with all factory programming, with the exception that the VEC sends a 65-70% fuel signal to the stock PCM because of the much larger injectors with the SC. The VEC takes over at 80%+ throttle. You can input fuel add/subtract in 250 RPM increments (based on your log results AFR) and you can also alter the timing based on engine load (MAP) and RPM on the ignition load page of the software.(+/-25 degrees of factory settings) I believe on SC engines, the VEC also intercepts the MAP signal to fool the PCM for increased voltage under boost.

The IAT sensor used is the OEM in the airbox, Prior to this new feature, the VEC 2 had no temp input, relying on the factory PCM offsets -- which was not really taking inducted temps into account. That's why I had 3 temperature tuned cards last yr. ranging from 40-100F. I still maintain till some one shows me the error of my thinking, that using the airbox temp and logging the results to an acceptable AFR, is a somewhat accurate number relative to the higher air charge temp at the intake manifold itself.

I believe max timing is 31 degrees for a GEN II car.
I think most log in 3rd gear.

You should ask these question to Sean himself. He has always been responsive to me. There are other, much more extensive, engine management systems out there, but they are much more money and not for the DIY guy....like me

Good luck

Steve
 

dun4791

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I am not the guy to go into depth on the spark part. I have chosen to use the spark curves Sean sent me initially with the purchase. Basically 6 degree retard at 5 pounds of boost with 93 octane gas. I have no water **** for cooling and a cast piston car. I don't really care about squeezing a few extra HP out of it. My 5 pounder runs quite strong enough for me the way it is. ( I toasted another 'sport bike' Friday night from 60-125, after being provoked of course ;) I have done extensive AFR tuning with the VEC. My VEC is an upgraded VEC 2 -- not quite the same as the VEC 3. I have only the old VEC 2 instructions.

That being said---as I understand it: the stock PCM controls the car in all closed loop operation with all factory programming, with the exception that the VEC sends a 65-70% fuel signal to the stock PCM because of the much larger injectors with the SC. The VEC takes over at 80%+ throttle. You can input fuel add/subtract in 250 RPM increments (based on your log results AFR) and you can also alter the timing based on engine load (MAP) and RPM on the ignition load page of the software.(+/-25 degrees of factory settings) I believe on SC engines, the VEC also intercepts the MAP signal to fool the PCM for increased voltage under boost.

The IAT sensor used is the OEM in the airbox, Prior to this new feature, the VEC 2 had no temp input, relying on the factory PCM offsets -- which was not really taking inducted temps into account. That's why I had 3 temperature tuned cards last yr. ranging from 40-100F. I still maintain till some one shows me the error of my thinking, that using the airbox temp and logging the results to an acceptable AFR, is a somewhat accurate number relative to the higher air charge temp at the intake manifold itself.

I believe max timing is 31 degrees for a GEN II car.
I think most log in 3rd gear.

You should ask these question to Sean himself. He has always been responsive to me. There are other, much more extensive, engine management systems out there, but they are much more money and not for the DIY guy....like me

Good luck

Steve
One thing to think about with logging the A/F based on the inlet temp, not the intake air temp, is that on a non aftercooled autorotor twin screw also without a heat exchanger, the temperature difference will not be on a constant differential between the two. This would also not take into effect the increased temperature differential created by heat soak which in my opinion would be very great on an unintercooled autorotor.

What size are the OE injectors, and the upgraded size?

It seems to me that the timing could be increased based on what octane you are running and the amount of air measured by the mass air flow sensor.

Next time you are out, I wonder what the A/F ratios would be compared from a 3rd to a 4th gear pull.

Isnt there a maf function, or is map just used?

Sorry dont know who Sean is?

What is the VEC3 price wise? Is anyone here on the board using a big stuff engine management system?
 
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Steve 00RT/10

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One thing to think about with logging the A/F based on the inlet temp, not the intake air temp, is that on a non aftercooled autorotor twin screw also without a heat exchanger, the temperature difference will not be on a constant differential between the two. This would also not take into effect the increased temperature differential created by heat soak which in my opinion would be very great on an unintercooled autorotor.

I understand what you're saying and agree........but If I set an upper temp limit of 126 for taking fuel out....and log /tune below that to 11.6 to 11.8...and am running the smallest pulley made...aren't I pretty safe?

What size are the OE injectors, and the upgraded size?

I believe 29s are stock and the SC injectors I got with the kit were either 50s or 55s.

It seems to me that the timing could be increased based on what octane you are running and the amount of air measured by the mass air flow sensor.

Again, you're probably right -- good tuners do remove some timing from Sean's stock cards. I am over 400 miles from the nearest dyno and/or tuner. I just did it myself and left the spark alone. Driveability was the guiding issue for me. Our car travels the country. I wanted keep it simple. With a cast piston car and no cooling.......I didn't want to take chances with any detonation

Next time you are out, I wonder what the A/F ratios would be compared from a 3rd to a 4th gear pull.

I've not actually logged in 4th, but the meter shows slightly richer in 4th --not much. If I'm
running 11.6-11.8 in 3rd at WOT.....4th will show about 11.3 - 11.5

Isnt there a maf function, or is map just used?

I believe it's all done with MAP

Sorry dont know who Sean is?

Sean Roe. He is the originator of the VECs (1,2,3) and Roe blower package

http://roeracing.com/

What is the VEC3 price wise? Is anyone here on the board using a big stuff engine management system?

I think it's about $1K. AEM seems the system of choice for the big boys

Steve
 
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Steve 00RT/10

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I now have one card which consistently gives me the AFR I want from 50F-95F. The trick is setting temp parameters and then balancing out the fuel add/subtract. It took a little monkeying around to find the balance point bewtween fuel add/subtract and IAT % correction........and may never be perfect, but it's working just fine right now. I'll run some 30F degree logs when I can in the next few weeks

My settings: +16.1 / -11% and temp parameters of 35F to 126.1F. Here is a screen shot of my settings.

iat-plain.jpg


Steve
 
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dun4791

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I now have one card which consistently gives me the AFR I want from 50F-95F. The trick is setting temp parameters and then balancing out the fuel add/subtract. It took a little monkeying around to find the balance point bewtween fuel add/subtract and IAT % correction........and may never be perfect, but it's working just fine right now. I'll run some 30F degree logs when I can in the next few weeks

My settings: +16.1 / -11% and temp parameters of 35F to 126.1F

Steve
Glad to see you worked it out. Its been a few months, and Ive been trying to learn as much of the tech specifically related to these cars. Im learning, but there is a shortage of Viper tech boards.
Im hoping the SCT tuner will help with the abilities of temperature compensating. Im considering doing a tt build, but Im going to see how the results from the SCT tuner stack up first. Well that and probably finding a 96-99 GTS to do it to.
 

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Steve's comment about not having the actual inlet air temp to use like the Paxton is a great point. For each pound of compression, the air temp increases by 10 degrees...so at 5lb boost, add 50 degrees to IAT (plus heat soak). So with a 90 degree IAT, plus probably 10-15 degree heat soak (gross IAT now around 105) at 5 lbs boost (+50 degrees), your inlet air temp is now 155 degrees. You can see the value of W/M injection and the role it plays in the 8-12 lb ROE cars. I wonder what the actual inlet air temp is at 5 lb boost with W/M...?? Folks say the inlet tubes are "cold" but that is still before the blower. Need a IAT sensor in the baseplate under the blower. That actually would be a pretty easy thing to do. Nonetheless, pretty significant inlet charge temps when you think you are driving around in a comfy 90 degrees.
 

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You know... if it helps you guys out, here is the IAT fuel correction numbers from the PCM itself:

Celsius : Multiplier
---------------------
-40 : 1.2382
-20 : 1.1757
0 : 1.1171
20 : 1.0372
33 : 1.0372
40 : 1.0372
191 : 1.9960

As you can see, the result is a parabola- which might explain some of your results. The PCM adds quite a bit of fuel when very cold, and as it approaches room temp, does next to nothing. The once it surpasses 40C, it climbs quickly.

Also, we can update your PCM's to whatever IAT settings you want -at the source- with the SCT-Flash software. Contact us for more information, or check out www.ViperSpecialtyPerformance.com/catalog
 
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Steve 00RT/10

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Daniel,

Interesting to know the actual OEM correction factors. Thanks for the info, but as you can see from my graph, the +/- % across the board is quite a bit different for my car. The other problem with the Roe system is that the IAT temp is not what's going into the engine. It may be somewhat relative for setting AFR add/subtracts, but even then it won't be quite right as it is not a linear equation -- as GR8 ASP tells me.

In order to use the SCT system, it would then follow that real world logging with the VEC would be needed to set the IAT parameters and fuel add/subtract. How else would you know what to input your SCT-Flash software? Inputting IAT parameters into the stock PCM would seem redundant if the VEC is already doing the same.

I guess my question would then be: If I have tuned my car to my satisfaction with the VEC....what other advantages would the SCT system afford me?.....and if one were to use this program---would the VEC then go away?

Thanks -- Steve
 

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Daniel,

Interesting to know the actual OEM correction factors. Thanks for the info, but as you can see from my graph, the +/- % across the board is quite a bit different for my car. The other problem with the Roe system is that the IAT temp is not what's going into the engine. It may be somewhat relative for setting AFR add/subtracts, but even then it won't be quite right as it is not a linear equation -- as GR8 ASP tells me.

In order to use the SCT system, it would then follow that real world logging with the VEC would be needed to set the IAT parameters and fuel add/subtract. How else would you know what to input your SCT-Flash software? Inputting IAT parameters into the stock PCM would seem redundant if the VEC is already doing the same.

I guess my question would then be: If I have tuned my car to my satisfaction with the VEC....what other advantages would the SCT system afford me?.....and if one were to use this program---would the VEC then go away?

Thanks -- Steve

Hi Steve,

We have found that the IAT settings for the stock PCM arent really that bad, for about 80 degrees ambient and below. The real problem occurs when the temp starts climbing. to keep AFR correct, fuel needs to be removed, not added. The reason they did this was to try and pull more heat out of the system. What we have done here is make the scale much more gradual so that it still will add a little cooling fuel in an emergency "extremely high IAT situation" but not so much, so fast, that it sends the AFR literally out to lunch. We also have the IAT increasing exponentially (to a much smaller limit) so that in normal IAT's, it wont be adding much fuel at all.

While it is redundant trying to get the IAT settings correct, you have to remember that all the VEC s doing is "fooling" the PCM into thinking it is colder/warmer than it really is. This does not take into account that the Spark is also based upon the ACT, effectively throwing it off as well. If changed at the source you change one thing, and one thing only.

To answer your question directly, for an NA car- YES, the VEC would go away. A car with a VEC will not be NEARLY as smooth as a car with a flash at the PCM level. The PCM can be scaled for injectors- correctly. The VEC cannot. All the VEC will scale is the "runnng" Pulsewidths, and do it too slowly for large injectors at that. There are about a dozen other settings that the VEC is not capable of scaling- and thats just for the injectors! The VEC cannot change your idle, how it idles, open/closed loop transitions, fan temps, OBD-2 System changes...... the list goes on and on. We are literally talking about AEM type adjustability, short of Boost Control. I have a H/C/Blower car here running 96lb P&H injectors 100% off the stock PCM for everything but boost. 2 months ago, that would not have been possible without an AEM- a VEC cannot handle injectors that big. I am even going to be giving 160lb injectors a stab soon, I think it can do them.

Depending on the car, the VEC may still be needed just for boost (adding fuel, pulling timing), but other than that, it will be doing zero- and the transitions will be much smoother.
 
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KenH

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Steve, thanks for posting your final settings. I was beginning to think the VEC3 was a bust based on lack of any info coming out of the tuning over the summer.

I am still running the VEC2 and upgrading to a VEC3 was going to be a high priority for me this summer based on the fact that my car would go from running so lean that it had detonation in the cool morning to running so rich that it would actually start stumbling until I pulled some fuel out in the hot afternoon last summer.

As it turns out, my AIT problems were very minor this summer compared to last. It finally dawned on me that the only change I made over the winter was to install the PBJ intake with the AIT mounted right in the intake airflow path. With the stock location, the AIT would climb up to 120F just idling in my garage. With the PBJ intake, the AIT would stay at just about room temperature doing the same thing. I think there may be some fairly significant improvement in this problem just by relocating the AIT. Now if someone can just figure out how to put it on the output side of the SC, we would be golden.

Daniel, I agree that moving some of the functionality changes back to the PCM, even with a VEC still in the system is likely to give a better overall result. The trick would be coming up with an optimized way for the two to play nicely.

--- Ken
 
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Steve 00RT/10

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Thanks Daniel,

Bear with me while I comment in between your explanation

Hi Steve,

We have found that the IAT settings for the stock PCM arent really that bad, for about 80 degrees ambient and below. The real problem occurs when the temp starts climbing. to keep AFR correct, fuel needs to be removed, not added. The reason they did this was to try and pull more heat out of the system. What we have done here is make the scale much more gradual so that it still will add a little cooling fuel in an emergency "extremely high IAT situation" but not so much, so fast, that it sends the AFR literally out to lunch. We also have the IAT increasing exponentially (to a much smaller limit) so that in normal IAT's, it wont be adding much fuel at all.

Please correct me if i'm wrong, but it is my understanding that the only influence the VEC has on the operation during closed loop is the base % injector set and individual cylinder trim. I have upped my base set from the factory 65% to 70% (to zero out LTFT) and some cylinder variance as well. My plugs are burning quite well the last 20,000 SC miles. I understand the fuel removal part as it gets hotter. In fact, the reason the stock PCM adds fuel is for cooling........liability, if you will. If you look at my graph, you'll see that I have opted to stop pulling fuel at 124F IAT at the airbox. That's around a 100F ambient day. If I'm not at the target AFR after that, it's OK with me. The boosted SC air will be much hotter.

While it is redundant trying to get the IAT settings correct, you have to remember that all the VEC s doing is "fooling" the PCM into thinking it is colder/warmer than it really is. This does not take into account that the Spark is also based upon the ACT, effectively throwing it off as well. If changed at the source you change one thing, and one thing only.

Again....I didn't think the VEC had anything to do with closed loop operation. Without this correction, you need more than one card for varying temps. I had 3 last year (50/70/90). At WOT, I'm using Sean's spark curves regardless of the fuel input and the IAT feature to help correct the AFR to my desired ratio. With a Roe, you would need a sensor where the boosted air goes into the engine, then it would seem the reflash would be more effective, regulating not just fuel, but spark as well.


Am I not thinking correctly?

To answer your question directly, for an NA car- YES, the VEC would go away. A car with a VEC will not be NEARLY as smooth as a car with a flash at the PCM level. The PCM can be scaled for injectors- correctly. The VEC cannot. All the VEC will scale is the "runnng" Pulsewidths, and do it too slowly for large injectors at that. There are about a dozen other settings that the VEC is not capable of scaling- and thats just for the injectors! The VEC cannot change your idle, how it idles, open/closed loop transitions, fan temps, OBD-2 System changes...... the list goes on and on. We are literally talking about AEM type adjustability, short of Boost Control. I have a H/C/Blower car here running 96lb P&H injectors 100% off the stock PCM for everything but boost. 2 months ago, that would not have been possible without an AEM- a VEC cannot handle injectors that big. I am even going to be giving 160lb injectors a stab soon, I think it can do them.

I'm not sure why I would want to change my idle?
I'm running the cooler t-stat. Even before installing it, I never ran hot -- even on track days ... so don't really need to turn the fan on sooner.

I have no intention of adding anything else to the car. I'm done. I'm quite happy where it's at. 5 pound Roe, No W/M, HS roller rockers, light flywheel, tubes, filters, 3:45s, Belanger headers, 3" Belanger exhaust, 96 PCM on the 2000 car. I have carefully added these bolt on things over the years always keeping drivability in the forefront. The SC was big step because it is getting into some other areas. The 5 pounder was the first kit out and probably the easiest, most reliable for a novice. 75,000 miles later with no mechanical problems and some hard running to boot, it seems to have worked out well (knock on wood)

Closed to open loop transition is a slight problem, but I think I am in safe where I'm at.

Depending on the car, the VEC may still be needed just for boost (adding fuel, pulling timing), but other than that, it will be doing zero- and the transitions will be much smoother.

My car doesn't miss a beat on transition. It literally explodes when you hit it. 3rd gear logs have me accelerating from 45-92 MPH in 3.6 to 4 seconds depending on outside temp. That's pretty darn quick considering that's way down around 2600 RPM in 3rd at the start.

I'm not adverse to trying something new, I'm just not sure that for me --where I'm at -- it would gain me anything?

Steve
 

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Hi Steve,

Oh Boy... this is going to take a minute.

I am not going to re-quote, I am just going to answer the paragraphs in Blue, 1-4 respectively.

1. The VEC most certainly can influence SOME closed loop activity. You did hit on two of then, scaling and trims- it can also change spark under closed loop. While it is true the PCM will adapt around the VEC with regards to base fuel tables, the IAT sensor is always being used for Spark, in Open and Closed loop. There are no Spark Adaptives- thus when you influence what the PCM "sees" by way of the VEC influencing the IAT signal, you are indeed influencing the spark tables as well, in both open and closed loop. You are correct in your thinking about the fuel/temp relationship.

2. Yes, you most certainly are thinking correctly. The benefit is two sided however. There is the "fixing the problem" side, then there is the "taking it as far as you can go with it" side. When you change one variable which inadvertantly changes another, you can quickly find yourself in a tail chasing game. Not to mention, you are trying to tune out en equation which isnt linear........ not easy.

3. Whether you need it or not is entirely your call, and whether or not you want to make other changes to the car beyond the what the VEC can do is also your call. There are inherent flaws in systems like the VEC that bring out instability in the system. For instance, when the VEC scales injectors back, it also effectively moves the pulsewidth. Move it far enough, and you are going to have all kinds of issues as you start spraying the back of a closed valve...literally. Hesitation issues, transient fuel becomes a mess, etc. It also does not scale below a certain RPM, making starting problems appear with very large injectors. Adding fuel on the other hand, works just fine- but only if you start from a zero base point, which requires scaling at the PCM level.

4. Lastly, the addition of a Roe SC is going to result in changes to the base fuel tables. These can ONLY be edited in the PCM, and if correct, will certainly net a better running car.
 
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Steve 00RT/10

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Steve, thanks for posting your final settings. I was beginning to think the VEC3 was a bust based on lack of any info coming out of the tuning over the summer.

I am still running the VEC2 and upgrading to a VEC3 was going to be a high priority for me this summer based on the fact that my car would go from running so lean that it had detonation in the cool morning to running so rich that it would actually start stumbling until I pulled some fuel out in the hot afternoon last summer.

As it turns out, my AIT problems were very minor this summer compared to last. It finally dawned on me that the only change I made over the winter was to install the PBJ intake with the AIT mounted right in the intake airflow path. With the stock location, the AIT would climb up to 120F just idling in my garage. With the PBJ intake, the AIT would stay at just about room temperature doing the same thing. I think there may be some fairly significant improvement in this problem just by relocating the AIT. Now if someone can just figure out how to put it on the output side of the SC, we would be golden.

Daniel, I agree that moving some of the functionality changes back to the PCM, even with a VEC still in the system is likely to give a better overall result. The trick would be coming up with an optimized way for the two to play nicely.

--- Ken

Ken,

In theory, you should be able to do a log -- no matter the temp -- and then dial in the IAT % from there, regardless of where the AFR is. The reality for me was to get a good AFR at a certain temp and then monkey with the % IAT. I tried the other way first, but didn't make much headway. The biggest thing to getting me off and running was to set temp parameters, which then made the curve much steeper in and out. At the stock settings of 10F-185F....the slope is too slight. I guess you could use really big numbers to offset the small slope. I chose to dial in a card and then start playing with the IAT. Took a while to arrive where I did, but I'm at the sweet spot for my car. 16% may be just a tad rich(11.3-11.6) right now, but I'll tweak that down a notch, if necessary, after running a 35F-40F log. I believe I can do whatever else with just the IAT input now. I also found, don't know why, that the 3 cards I had last year -- pretty well dialed in -- were too rich on the upgraded VEC 2. If the cold log holds true, this will have been very well worth the effort.
Heck, it was still worth the effort because I've covered 90% of the miles I drive already with the setting I've arrived at.

I hate to raise the Vipair spectre again, but our car with it runs a cooler IAT in all circumstances than the car without it. Log runs for example: Vipair car 86F ambient, 102 IAT. Non Vipair car 87F ambient, 128F IAT. Some runs were not that far apart, but the difference was significant nonetheless

Steve
 

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Question for you guys: Does the VEC3 IAT feature only kick in during open look operation? The reason I ask is that I experimented with the IAT feature over the summer and accidentally set the low range temp below 70 degrees. When I started the car it idled horribly lean. When I reset the IAT feature the car idled normal again. After a few experiments like this I came to the conclusion that the Vec3 IAT feature works during both Closed and Open loop. Is this correct?
 
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Steve 00RT/10

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I thought it only functioned in open loop, but it seems some think it applies to closed loop as well.

I don't see how just setting the low temp could impact the car. It comes defaulted to 10F-185F. Mine is at 35F now. What percent fuel add / subtract did you have in there? You should be on the plus side as the temp goes down.

Steve
 

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Steve, I don't remember the settings that caused this but I do know that I subtracted too much fuel in the lower temp range and it idled very lean and ran like a wet noodle accelerating from 1st to 2nd. My AFR was in the 16's. When I changed my IAT settings and/or turned it off completely, idle and AFR was fine. I repeated this experiment in closed loop operation a few times. This leads me to believe that the Vec3 IAT works full-time or I have a defective unit. My Vec3 arrived with the IAT turned off (low/hi air temp correction set to 0%). I'll ask Sean about this as well. Just thought I'd put it out there since we're on the subject of IAT.
 

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Steve's comment about not having the actual inlet air temp to use like the Paxton is a great point. For each pound of compression, the air temp increases by 10 degrees...so at 5lb boost, add 50 degrees to IAT (plus heat soak). So with a 90 degree IAT, plus probably 10-15 degree heat soak (gross IAT now around 105) at 5 lbs boost (+50 degrees), your inlet air temp is now 155 degrees. You can see the value of W/M injection and the role it plays in the 8-12 lb ROE cars. I wonder what the actual inlet air temp is at 5 lb boost with W/M...?? Folks say the inlet tubes are "cold" but that is still before the blower. Need a IAT sensor in the baseplate under the blower. That actually would be a pretty easy thing to do. Nonetheless, pretty significant inlet charge temps when you think you are driving around in a comfy 90 degrees.


Agreed an IAT2 sensor in the manifold would be the best place to temperature sample for the most correct fuel corrections.
 
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