Fueling and Airflow tables

[Blue02WS6]

Are the numbers in the MAF and VE tables the amount of "AIR" used to calculate the AFR at any given moment in the tune based upon the physical amount of fuel going in to the cylinders at that moment? If so does the higher numbers mean more air is being used to calculate the given AFR?

[jimmyblue]

Yes, those tables are used to derive cylinder air mass
(MAF is mass flow; VE table is a coefficient to the
MAP*RPM*displacement*{temp etc.} speed density
calculation used in the Dynamic Airflow number - a
lot of fudging and blending, stuff you can see and stuff
you can't, is in that. The air flow and air mass are used
directly and for things like calculating motor torque,
indexing the spark table and so on.

With commanded AFR and some injector flow & nonidealities
info, injector PW is figured from cylinder air mass.

[Blue02WS6]

Ok...then the amount of air needed is based upon?...how much actual fuel there is in the cylinder and
the amount of spark advance being the main factors?
And the amount of fuel is a product of the injector Flow rate and the cam as being the
main factors for that?

[68Camaro]

then the amount of air needed is based upon?...how much actual fuel there is in the cylinder and
the amount of spark advance being the main factors?

Engines are air pumps - we measure how much air the engine is taking in (maf) or calculate how much airflow (map sensor reading along with iat, engine displacement = speed density) and then we meter fuel accordingly to how much air the engine is actually ingesting. When we make changes to the engine for increased power (cylinder head porting, camshaft, headers, + intake) we are changing how much air the engine will pump and thus the need for a different calibration (tune) for the fueling required for said engine.

I hope this is what you were asking for?

[Blue02WS6]

Not sure how to ask what I want to know therefore I will go in steps and learn along the way

The engine is basically static, I like the analogy that it is an air pump...that helps, now with the
addition of a bigger cam, ported TB and intake, headers and duals we have increased how much
air the engine pumps and therefore how much fuel it will require to calculate the A/F ratio.
It appears to me that the air has much more ability to be changed in the tune and the fuel not so much,
Is the fuel amount the engine gets mainly a product of the hardware (cam, injectors, etc) or software
(IFR tables, spark? etc.) or a combo of these?

[68Camaro]

It appears to me that the air has much more ability to be changed in the tune and the fuel not so much

,

The "air" tables control fueling. The airflow through an engine is determined by cylinder head + intake + exhaust efficiency and camshaft selection. The VE table (volumetric efficiency) in any given cell (where the rpm and manifold absolute pressure meet) state how much air should be inside the cylinder (0% = empty, 100% = full) and the pcm will command x amount of fuel based on measured (maf) and/or calculated (SD) airflow. We don't actually change the airflow with the tune but calibrate it to what the airflow is in reality. When all of our hard parts change and the engines airflow characteristics change the stock calibration goes out the window.

Is the fuel amount the engine gets mainly a product of the hardware (cam, injectors, etc) or software
(IFR tables, spark? etc.) or a combo of these?

Fueling is controlled by measured and/or calculated airflow by the pcm. IFR tables along with other injector tables will change with different injectors. When going from stock injectors (say 28# to 110#) these tables are how the pcm knows how much fuel will flow at any given pulsewidth for said injector.

Hope this makes sense and doesn't come off as babble.

[Blue02WS6]

Thanks for the help...and no this is not babble to me, I need to know the small stuff to make my mind work.

for the VE, how can I have values of over 100 in my VE table? If 100% is full?
Even the HP help says this can happen if I remember correctly.

So is the amount of air or airflow a mechanical and fixed thing? Or can we get any table(s) out of whack
that makes the engine think it's getting x amount of air when it's really getting xxx amount and screw
up the AFR by then having to add xxx amount of fuel to bring it back to stoich?

[68Camaro]

for the VE, how can I have values of over 100 in my VE table? If 100% is full?

When all parts are matched well (intake runner size and efficiency, cylinder head size and efficiency, exhaust port and header, and camshaft selection) it is possible to achieve over 100% VE due to taking advantage of dynamic airflow. The scavenging of the exhaust rushing out helps to draw in the intake charge then the piston traveling down in bore continues to accelerate the intake charge in the cylinder head/intake runner - once the piston reaches the bottom and starts back up the inertia of the intake charge keeps airflow moving into the cylinder and then a properly timed camshaft will close the intake valve at just the precise moment to capture the maximum amount of air in the cylinder - dynamic airflow has just filled our cylinder to over 100% VE hopefully. When you understand this all things like camshaft selection, intake runner length and volume, header size and length all start to fit into the puzzle and why all parts need to match for the intended rpm range and cubic inch size of the engine being built. This has been for a naturally aspirated scenario - boosted is a little different.

So is the amount of air or airflow a mechanical and fixed thing? Or can we get any table(s) out of whack
that makes the engine think it's getting x amount of air when it's really getting xxx amount and screw
up the AFR by then having to add xxx amount of fuel to bring it back to stoich?

yes - thus requiring tuning to bring all back in line.

Hope this helps.

[Blue02WS6]

Yes this is helping...When I bought my HPT it was because two tuners had a crack at my tune
and after paying some major $$$ if you know what "tuners" charge the best I got was 30* of
spark with 900 rpm idle and the idle still sucked what I knew about tuning was throwing some
plugs in and turning the distributor So do I buy HPT, try to learn and do it myself or keep
throwing money away...

Why I have been asking these questions is I want to understand how this works on a precise level,
maybe I can get some ideas what I need to do...the car runs real good and the two dyno kings had
the top end in pretty good shape as my 224 cam with an A4 put down almost 400 HP and TQ to the
rears but a 900 rpm idle that still wants to stall. I think I have read every thread on idle tuning and
followed most of the suggestions, some seemed to help, others not. I have messed with almost every
table associated with the idle just to see what happens, but not knowing what I am really doing to the
engine, I am kinda shooting in the dark...I have fine tuned the VE, MAF and RAF and have them closer
than they were and it has let me lower the idle to about 750 and that's not to bad, still seems like it wants
to stall sometimes so I am still trying to learn what is happening so maybe I can figure out where to go.
The engine likes over 40* at idle to achieve a map of about 41 kpa or so, and you hear less lope but the
idle seems more stable, but I have to get over 40* of spark so I thought with that much spark, could it
be because it is getting to much fuel? And if so, has that happened in the tune or is it just a product of
the setup, the cam, ported intake, and LT's and 2.5" duals?

[HartRod]

Very good discussion here! What injectors are you running and do you have all the correct data entered for them? (flow rate vs. press delta, offset vs pressure delta vs IGNV, short pulse adder, and min pulse) If not, I would work on that. If those aren't correct, you will be chasing your tail....I found this out the hard way, LOL.

[68Camaro]

larger camshafts, ported heads and intakes (read larger runners), and bigger exhaust causes the airflow to be slower at low rpm and therefore less inertia in the airmass flowing into the cylinders and less cylinder filling at low rpms - this is a trade off we are willing to make for upper rpm horsepower and torque gains! Now since we are not moving as much air into the cylinder at lower rpms the VE table will need to be tuned accordingly (leaned out at low rpm's and more fuel at high rpm's provided all of our mods are truly working together for increased airflow up top!). The only way to do all this tuning accurately is with a good quality wideband O2 sensor (I hope you have one). When tuning idle I will force the idle just as low as I possibly can (using the bi-directional controls in the scanner) can so I can tune the VE cells good. Idle timing of 40* is too high - 22* to 24* usually works well. If the idle timing is too high already and idle rpm starts to drop the pcm will command more timing with the underspeed spark table (hopefully if it is setup properly) but if the engine is already at MBT timing (mean best torque) adding more timing will not help to catch the falling rpm.

once again I hope this is helpful.

p.s. - probably the most useful idle tuning advice I have read on here is a writeup done by soundengineer. it is stickied along with some other write-ups on idle tuning or just check some of my threads because I re-posted it awhile back thanking him for it.

p.s.s - as HartRod stated your injector data needs to be correct also

[Blue02WS6]

Very good discussion here! What injectors are you running and do you have all the correct data entered for them? (flow rate vs. press delta, offset vs pressure delta vs IGNV, short pulse adder, and min pulse) If not, I would work on that. If those aren't correct, you will be chasing your tail....I found this out the hard way, LOL.

I have not messed with the intake manifold (LS6) or injectors and have left the injector flow rate, etc in the tune stock, I assumed those items connected with the injectors did not need to be tuned, is this correct?

[68Camaro]

I have not messed with the intake manifold (LS6) or injectors and have left the injector flow rate, etc in the tune stock, I assumed those items connected with the injectors did not need to be tuned, is this correct?

that is correct. you will only need to change that data if you change your injectors.

[Blue02WS6]

68Camero
At idle, I have CL commanded at 140*, I can lean up the VE for the idle cells and I appreciate that idea
and bring my spark in line to the mid 20's but do I need to artificially do the same with the MAF table?
a red flag is waving in my mind thinking about the MAF table, but the two or three cells I will mess with
are only used for idle when the car is at a stop, are these few cells all I need to mess with to help solve this?

And yes I think I have read every thread by soundengineer and know the thread you referred to, I found it
helpful but if I recall one very good thread about idle from one of the big guys and maybe it was this one
we are discussing talked about drilling the TB blade hole...I don't know if this is really a good idea and you
can't undo it once it is done and I have not, actually on my first non-ported TB I followed that advise and it
did not seem to help much and have read that it can actually hurt trying to scan and tune it correctly.

[68Camaro]

I force it OLSD and tune the VE table first with a wideband for reference - forcing the idle up and down as high and low as I can get it so more cells are covered and then hand blend cells that you are unable to hit (you will be able to see the trend as you are tuning). Getting the fueling in line first makes a huge difference in idle quality. Tune the MAF last after all is well in OLSD.

I almost always drill the throttle blade on cammed DBC setups. The reason for this is to keep the IAC counts in a good responsive range (50-80 counts) so it can do its job. If you just try to open the throttle blade for more idle air (bigger cams need more idle air because of their increased overlap vacuum is lost and the engine is just unable to draw as much air through the same opening as before - so therefore we need to increase the idle air opening) the TPS volts gets to high and goes outside the pcm's window for acceptable idle TPS voltage and causes problems. You can open the throttle blade some as long as TPS voltage doesn't go above .67 volts at idle (I think this is the correct voltage) - if you still can't get enough idle air then you need to drill the throttle blade (just take small steps here - timing and fueling need to be very close before final tweaking to hole in the throttle blade).

[Blue02WS6]

I see I still have some tuning to do

After I force the idle up and down as far as I can, how many cells in each direction do I blend to my existing VE values?
And what AFR do I want to command for the areas I can actually hit, say 15:0-15:4 or is that to lean?