Boost Compensation tuning explained (again) MicroSecBit too!

[BLKMGK]

Okay, I'm home sick as a dog with the SO and have just typed up for someone how to tune Boost Comp via a PM. Since everyone keeps asking about this I'm going to also post what I've typed here to help others understand. Here goes:

Well, you need to get the car running and driving first before you can do this.

Lemme' briefly explain the concept behind Boost Compensation tuning - If at say 4K RPM and 100KPA you need X amount of fuel to get Y A/F then at 4K RPM and 200KPA you will need 2X fuel to get the same Y A/F. Make sense? Yes, in extreme cases the VE of the motor will change at some point due to restrictions somewhere but for the most part this concept holds true.

If you look at a Full Boost Comp'd mapping you will see that all fuel columns are the same vertically. The way that fuel is taken care of is there's a Fuel Modifier table called Boost Fuel Correction. This is setup usually so that say 100KPA is a "zero point" - no change (the zero point can be anywhere you choose). But 200KPA effects a +100% change in fuel and 0KPA is a -100% change in fueling. Points in between are linear. Making sense so far?

Now - you can Boost Comp a mapping that's done cell by cell just by applying those % changes to the existing map. The effect is greater granularity in fueling although you MAY need to modify something called the MicrosecBit. MicroSecBit defines the number "1" in the RAW view of the fuel map - more on that later Okay, so you now have a mapping that is Boost Comp'd but numbers up and down are not the same - should drive as fine as the original map. You can stop at this point or go further. IF you stop here, as I did once upon a time, and tune multiple load rows for the same A/F you'll get a surprise as they all become the same number

Okay, go do a WOT pull at the lowest load value your W/G will allow - easy if it's a N/A motor! Tune that load row to whatever A/F you need WOT and make the cells above and below that load the same so there's no interpolation. If you take those numbers you get and apply them anywhere you go WOT you should find that you maintain the same A/F in those load areas that you tuned for. You now have what I call a "Hybrid" Boost Comp map because the vac areas are cell by cell. You can leave that if you want.

To get the vac area done for a "full" Boost Comp map continue copying those same numbers down vertically - the car will now run pig rich. Go into a table called the Throttle Inj Modifier. Adjust the table so that at idle you have a decent A/F and then go for a drive. At cruising speed\throttle adjust the table so that you get a decent cruise A/F and then calculate between the two points to get a linear table. Play with this some but in the end you'll have a table that removes more fuel as the throttle is closed (mine is -26%) and less at say 50% throttle (mine is -3%) in a linear table. Ta Da - "full" Boost Comp.

Another way to do those vac areas is to do a little math. Say you want 12:1 in one row but the vertical numbers give you 11.5:1 - calculate the percentage of difference between the two and either apply that to the Boost Fuel Correction table for that load range or to the fuel table load area. Do this for every area you want something other than whatever your WOT fueling was. In this case there's NO Throttle Mod table filled in. So, why do it this way? Because some small turbos will spool at part throttle - say on hills and things. With Full Boost Comp it's also possible to get into a situation where say the car is lugging on a hill and more throttle just makes it go pig rich but load doesn't go up quickly. I'm actually about to convert to this method to try it out.

Make sense? Lot's of ways to skin this cat!

[BLKMGK]

Bummer - can't attach files here or I'd add examples to this post. AEM can ya' help me out here?

First this setting can only be found if you look at the Options, Full List. It's called MicroSec/bit.

Okay - so what's MicroSecBit? Pull up the Fuel Map, Right Click, View RAW. The numbers in those cells can be between 0-255. Look at peak torque at peak load - are you close to 255? Now look at idle - are you close to 0? You can actually have 255 in one of those cells and NOT have full fueling! You can also have very small numbers in the idle area and find that making changes as small as one increment will swing A/F by a LARGE amount. Neither of these situations is one that you want. LEts say the idle range has a number of 10 in it - moving to 11 you swing fueling by 1/10th - that's alot! My idle numbers are over 100 - now THAT is granularity. MicroSecBit or MSecBit is what defines the value of "1" in the fuel table. You CAN modify it!

So, before yuo go playing with that number realize it will have BIG impacts on your fueling. Here's how you change it "safely". Open the fuel map, right click, View Duty Cycle. Highlight the ENTIRE map, right click, Copy to clipboard. Now modify MSecBit up or down and then Paste the fuel mapping back while still looking at Duty Cycle. Right Click, View RAW. Any numbers over 255? IF yes then MSecBit is too small, switch back to Duty Cycle view, make it bigger, Paste the previously saved table, and check the RAW view again until the numbers are big but not huge. Note that if you use Boost Comp as explained above you'll also gain granularity. Doen CORRECTLY fueling shouldn't change much and the car shouldn't need too much retuning when you now upload this mapping to the ECU.

Make sense?

[WadZii]

when you change microbit/sec you will also have to modify the crank time table ( the main table in the startup template).  i devised this forumula to correctly change that table.  we will assume the crank time table is all set to one number

CT1=orignal number in the crank time table
MBS1= orignal micro bit/sec
MBS2= new microbit/sec
CT2= new value for the crank time table

(CT1*MBS1)/(MBS2)=CT2

changin microbit sec will also get you alot more resolution for cranking so you can dial that in better.

the key to getting boost comp tuned right is to make sure afr at WOT is flat first.  dont worry with fine tuning the throttle inj corr table untill WOT is right.

a formula i use to setup the boost comt table is as follows. (i use PSIg, you can modify this for kpa..but i never use kpa )

min=map min value (ex.. -13.9psi)
max = map max value (ex.. 60psi in the case of hte 5bar sensor)

min/14.7*100= %correction at min
max/14.7*100= %correction at max

enter those 2 points and use the calculate function to create a straight line betwen those 2 points.


more tips for tuning the throttle inj corr table.
set that table up on the highway cruising in a high gear.  if the car dosnt idle or drive well at low rpms, modify the fuel map (making sure to change the whole column).  It's ok for the fuel map to be leaner in the lower rpms.. usually you will make more power that way anyhow.

[TurboTeg92GSR]

My MicroSec/bit is 40, running a fully boost comp'ed map, and all my RAW numbers are between about 100 and 120. Is there any reason I shouldn't just lower the MicroSec/bit to the point that all my RAW numbers are about double what they are now?

[GTRSentra]

BLKMGK
Great Info.
Keep in mind that there are some of us here that really appreciate this kind of help (tutorial) even when it is not publicly expressed.  
Pito

[WadZii]

turboteg... numbers around 100 work pretty well.  the only reason i would make any changes is if you needed finer control of the fueling.

[Alstare]

Thanks again guys for yet another well written thread on setting up boost comp.

One quick qeuestion on the throttle mod table setup, just to clarify.  You suggest driving in top gear on the highway to do it...

I assume you would want to turn off o2FB<obviously> and then drive at each tuning point TPS% wise on the throttle mod 2D table and adjust accordingly to achieve your target AFR for that RPM.

Also will you be able to see when on our particular setup where to stop trimming fuel via the throttle mod table?  I know we mostly all use around 50%-60% range to return normal 0% trim, but with this method described above shouldn't it show where your setup will begin requiring 0% fuel trim via the throttle mod table?

Thanks again, I'm sure this thread will help alot of people starting out with a BC Map, I knwo the previous one helped me alot.

[WadZii]

to tune the 0 to about 20 or 25% throttle areas of the throttle mod table use top gear, past that you will need to use lower gears driving around town.. you will be able to see when throttle mod needs to go back to 0.. usually around 50 or 60% throttle.

[BLKMGK]

Good additions Wadzii! I've been using a spreadhseet to do the Comp table itself but I like your way of doing it - sounds easier! I also appreciate you pointing out the Crank Fueling stuff - I'd forgotten about that completely 8O Might explain why I've had to diddle those numbers so much in the past

Honestly - I've explained this stuff here at least a few times and the short version of it via PM a TON This one I'm adding to my sig!

Now - since after reading the above folks are probably realizing that what we're talking about is "just math" let me throw this one at ya'. If I'm at 10:1 but want 14:1 WOT then do the math to find the [percentage of difference and Bingo! you're in the ballpark. This is how folks can dial in fuel quickly on a dyno or in my case on the street with my left foot on the brake!

Note that this is WOT, I believe that throttle changes VE with a restriction so it might not be so easy - not tried it for part throttle yet. The calc method I mentioned above to figure A/F without Throttle Mod contradicts this though so that's part of the reason I want to try that method out! My turbo spools slowly enough that hills aren't an issue but under boost letting off the gas I do see a brief lean moment occasionally - nothing I deem worthy of sweating but I want to see how this method works. Just need to find some time!

P.S. On high output motors you may find that in the high load areas this method of tuning might not hold 100% true. IMO this is where restrictions begin to show up - TB, intercooler, out of the compressor effeciency island, exhaust backpressure - you get the idea. I woudl tune this in the Boost Comp table not the fuel table but YMMV. I've yet to see this myself - not making enough power!

[WadZii]

good point blk.. really high boost and/or really low boost will require some changes due to compressor/turbine efficency.. this can be done in the boost comp table.  i have had this problem with running alot of boost on a garret gt28rs at 20psi.

[blown1]

Right Click, View RAW. Any numbers over 255? IF yes then MSecBit is too small,

So ideally, what do we want to see for numbers in Raw ? Is the goal to get near 255 without going over ? I have 4 cells with 255 near peak tq and at idle they are 19 to 25.  I still have a lot to figure out to do this, but I'm working on it.

Thanks for the post BLKMGK.

[WadZii]

if the numbers are near 255 and the tune is pretty much done then you are fine.. but keep in mind when you make a change to the car you may run out of room. 255 is the max raw number.

personally when i tune a car with full boost comp mapping i like to see the numbers average around 200 when im done.  that leaves about 25% more headroom for future changes and really good resolution.

[blown1]

if the numbers are near 255 and the tune is pretty much done then you are fine.. but keep in mind when you make a change to the car you may run out of room. 255 is the max raw number.

personally when i tune a car with full boost comp mapping i like to see the numbers average around 200 when im done.  that leaves about 25% more headroom for future changes and really good resolution.

Thanks, I will need a little room to grow. I am at 80 msecbit......looks like I need to change to 90 or a touch more. I figured the msecbit should be correct before I start getting my a$$ kicked again  

[blown1]

Where/how do I change my boost fuel correct table ? Looking at the other boost comp thread I think I need something above and below the "zero" line. I would love to see some other folks boost fuel table and throttle inj corr tables.
BLKMGK, if you want me to post the attachments for you just e-mail them to me. tarmour@catt.com

[BLKMGK]

Where/how do I change my boost fuel correct table ? Looking at the other boost comp thread I think I need something above and below the "zero" line. I would love to see some other folks boost fuel table and throttle inj corr tables.
BLKMGK, if you want me to post the attachments for you just e-mail them to me. tarmour@catt.com

Will send you one of my maps in a moment. It'll make much more sense to you then I think