Tuning FAQ

[warmonger]

We're going to start this forum off by putting in some excerpts from previous posts related to tuning with this setup.
I also want to point out that most any comprehensive tuning solution will use similar methods so this isn't just XCAL and SCT specific.

Lets get it rolling. :cool:

[warmonger]

Okay, here is a recent post from CEG with a question about MAF tuning and I tried to explain a reasonable method for figuring out the MAF transfer function from sensor data that you have available in the car.

I'll put it in Italics and this way it'll be easy to read the questions and answers:
__________________________________________________ _________________
Ok. Thay is what i wanted to know. I have the PRP, but i wasn't sure if the MAF HAD TO BE programmed for your injectors. So i can just use Advantage to setup a Pro-M 75mm MAF to run on some 24# Accel's i have??? I kinda have another car to drive that gets about 40mpg so i wanted to start seriously messing with this software i spent 600 bucks on lol.

I am getting pretty familiar with the software now...but i really do not know how to come up with a MAF Transfer Function. Isn't there a "manual" that SCT makes that explains how to tune using their software?

And just to get this straight...if i buy a Pro-M 75mm MAF i will not have to get it reprogrammed for injectors...i can tune it in using the software i already have correct?



Yes and yes.

Demon SVT tuned in his ProM maf very nicely and still uses it. As long as it is working fine and consistently then there is no problem using the ProM.

If you don't have the sheet on the pro-m then you have to use a little reasoning to get into the ballpark so you can figure out the transfer function.

Here is how you do it:
1. determine what car/engine the pro-m was designed for
2. determine what injector size it was altered to meet
3. Grab the stock MAF transfer function for the car in step 1 and load the values of airflow (in kg/hr or cfm or whatever) versus voltage into an excel spreadsheet in two columns.
4. Ask yourself: Is the ProM sized for injectors that are different than the car in step one originally came with?
5. Calculate percent difference in injector size then multiply the airflow values in your spreadsheet by this percent difference and create a new row of values.

This is a ballpark figure for the ProM transfer function that you can load into your PRP software. You need something like 30 datapoints for loading into the software, AND you will need to convert to mass/tic measurements.
This is really just another multiplier so you can make another column next to your computed PRoM data and multiply it by the correct scalar.

I'm feeling nice so I'll look it up for you
Divide by 15,000,000 or 15x10^-7 if you prefer scientific notation.
So you you take all cells with the computed ProM function (corrected for injector size) and then divide each number by 15E-7 and you will have a value in mass/tic that you can load directly into the PRP software.
This just gets you into the ballpark now and you will have to pay attention to your long-term fuel trims to see how far off the this will be.
Lets say for example after one day of driving on this new computed Maf function you observe most of the fuel trims to be -8% to -15% at various rpms when you datalog. Well take that as about an average of 10% too rich, then go to your spreadsheet and multiply all values by about 0.90 or 90% and reload the function into your PRP. The drive and retest.

Lets say that at idle your Longterm fuel trims are showing small values of +3 left bank and -5 right bank. Within +/- 5% you should leave the Maf function alone at idle, assuming your idle quality is good. However, when you are driving around at 50mph cruise, the fuel trims are +10% and +13% on each bank. The plus values show that at that driving range you are too lean. The cruise portion is going to be in the 1.5-2.5 volts range (normally) and you will have to correct that. THe idle portion of the MAF flow usually runs from about 0.6volts to about 1.0volts. In this example your idle is good but your cruise is not. So you will have to multiply the 1.5-2.5% range by 1.10 or add and extra 10% to the curve.

At this point you will be manipulating pieces of the function and the function will no longer be smooth. Graph the function in excel. Look at the general trend of the graph and see what the shape of the curve should look like if it were smooth. They usually look like a weak exponential or a wierd 3rd order polynomial (if you know anything about basic math). Whatever, thats just bonus info but all you've got to do is smooth the transition from Idle to Cruise voltages to finish the job.
Yes this means going value by value from around 1.0volts to 1.5 or higher and "tapering" the multiplier from nothing at idle up to 10% more fuel at cruise, then you may as well pull that 10% all the way to 5Volts.

right?
If you play with these curves in excel a couple of times you'll get a feel for how to dial this in. If you have a wideband you then test your WOT values, or get on a dyno. Then you can finish your MAF function because it usually takes WOT test with a wideband to truly determine what the MAF function is above say 3volts. Once you do that, re-smooth out the function so that it is a nice curve and load it into your car, clear the memory and drive it. Viola, you have a perfectly tuned-in MAF. The beauty of this is that you can boost all day long and the changes in fuel will automatically be calculated for as long as you are drawing in air within the MAF's range and the PCM will keep the A/F right in a safe range the whole time!

You see, this is the kind of Post that I wanted to have a ProRacer pack tuning forum for.

[warmonger]

Much of the tuning problems that I and others encountered came from people trying to be too clever and changing things that didn't need changing, or using advice of guys experienced on OBDI and earlier systems, or just changing too much stuff at one time and unable to isolate a problem.

To start off, make sure the PCV and crankcase ventilation system is set up correctly on a FI car. Here is a drawing Stazi made for CEG after we hammered out all the why/what-for questions that is pretty much the only Correct Way if you want to eliminate unknown influences while tuning.
See this image in the link below:
http://www.gtxr.net/turbo-vacuum-schematic.pdf

This is a schematic of the lines and how they should be hooked up. It's quick but accurate and easy enough to follow like a vacuum schematic.

[warmonger]

Okay, here is a response to questions about injector sizing and calculating airflow. Some decent stuff in it:

What about going from 17# to 19#? How much must be adjusted there? Will the upgrade in engine size compensate for the 2# increase?ou have to think in percentage of increase because that is the only way to get correct perspective.
The 3L is 20% larger than the 2.5L
The 19# injectors are 11% larger than the 17# injectors and on average will flow ~10% more fuel if swapped out. So just by doing this you have increased fuel flow by 10% but remember you may not need the full 10% increase at idle.
19#'s will work and can probably by compensated for by an eManage or SAFC if you just add about 8-10% fuel AFTER you install the injectors (again, Idle is a different story).
This won't be perfect, but it will work until you get to a dyno with A/F to tune it.
However, this brings another problem up. The top end of your airflow through the stock MAF will be maxed out at about 4.5 volts. This is because the emanage will add 0.45 volts on top of the 4.5 volts from the MAF to compensate for the additional 10% fuel you are asking for. The output voltage of the emanage going to your PCM will then be 4.95 volts even though the MAF is still only putting out 4.5v.
All you have to do now is figure out what airflow voltage the 4.5 volts is equivalent to and then see if that is enough peak airflow for the new 3.0L at max RPM.

Figure out your max airflow at max RPM = 7000:
3L has an 89mm bore x 79.5mm stroke.

44.5^2*PI= 6221 mm^2
6221x79.5 = 494580 mm^3 per cylinder
Convert from cubic mm to cubic feet:

494580 / 25.4^3 (in^3/mm^3) = 30.18 in^3
30.18 per cylinder x 6 cylinders = 181.1 cubic inches and is the way you calculate engine displacement.

30.18 / 12^3 (ft^3/in^3) = 1.747x10^-2 ft^3 of air per cylinder.
0.1048 ft^3 is the engine displacement in ft^3.

How many cylinders draw air at any given rpm:
7000 rpm / 2 = 3500 (because two revolutions per firing cycle)

# cylinders x vol. per cylinder:
3500 intake cycles/minute x 0.1048 ft^3/intake cycle = 366.8 CFM (cubic feet/minute)

OK. ~367 CFM at 7000 rpm. This can help you size your MAF correctly or see if your current MAF can actually go this high. Honestly this is right around the top range of the SVT MAF calibration so I don't know if your stock duratech MAF goes this high. However if you find out that it's close then you will be able to use it because you are almost never at 100% volumetric efficiency...which is what this math calculation assumes to be true. More likely at 7000 rpm you are 80% of that.

80% of 367 = 293 CFM
Now, does the 4.5 volts on your stock MAF correspond to 300 CFM or more? If it is more than say 10% less (i.e. 270 cfm) then you will not be able to safely use your stock MAF even with the 19# injectors, and DEFINITELY not with 24# injectors.

If you change the MAF then you are now in the other category where you must get a chip because you have changed TWO VARIABLES from the engine mangagement system (MAF and INJ) and now you cannot control it very easily with a simple MAF scaling device. It is possible with lots of tuning time to use something like the emanage with rpm and throttle position and 256 data points to get a close approximation, but it is never perfect. The best I ever got was with the stock MAF and 24# injectors. When I tried a non-stock maf and 24# injectors I had CEL's popping on at random engine speeds during cruise. Not the best way.

[TrackCat]

Go check out
www.EFI101.com theres a forum on EFI tuning

[scrupul0us]

this is definately a far cry from being a FAQ... basic questions like:
-what is a tune
-when do i need a tune
-what do i need to tune
-what are the expected costs
-do you need a chip
-various chip options
-pros
-cons
-mod alternations -> chip alterations
-etc

should be addressed here and from the point of the total newb... think, tuning for dummies, not, tuning recap for tuners

cant really expect anyone to learn a thing from staring at injector constants and cfm flows when they dont even know why they are here to begin with

theres definately some learned people here on the subject... so get on it ;)

just my .02

[warmonger]

this is definately a far cry from being a FAQ... basic questions like:
-what is a tune
-when do i need a tune
-what do i need to tune
-what are the expected costs
-do you need a chip
-various chip options
-pros
-cons
-mod alternations -> chip alterations
-etc

should be addressed here and from the point of the total newb... think, tuning for dummies, not, tuning recap for tuners

cant really expect anyone to learn a thing from staring at injector constants and cfm flows when they dont even know why they are here to begin with

theres definately some learned people here on the subject... so get on it ;)

just my .02


Cool. Nice input.
Now I'm appointing you my FAQ guru so I want you to answer those questions you posed and we'll pin them when you're done. :biggrin:

Remember, your work will speak for itself so do a good job.

[Bigoudi]

May want to throw in a "where to buy" question to that list, since that is frequently asked. I've seen other places pop up aside from ADC lately.

Greg

[warmonger]

True.

The best thing to do is go to http://www.sctflash.com and look for the nearest dealer. If you have none near then go with your favorite recommeded dealer.
such as ADC or Brenspeed.

[CheeseEater88]

any piggy back ECUs for the I4 Cougars?