now since water can cool faster, more humid air going in the engine will absorb heat faster. so waht the sensors are measuring arent close to actual conditions. which is my reasoning for taking most error out of the system as possible

 

hp tuners: This table is used to calibrate the MAF sensor. The MAF sensor works by outputting a frequency signal that is proportional to the airflow through the meter. This table is used to lookup the Airflow (g/sec) value for a given frequency and ultimately calculate the Airmass (g/cyl) used for fuelling calculations. If you modify your MAF meter you will likely have to modify this table.

The frequency is proportional to the amount of air entering but is not a direct measure of the air that is later extrapulated. So I would think that gm engineers measured the amount of air that can be taken into the stock engine at a certain frequecy and set it up accordingly. Of course mods mean more air and though a certain freq is being measured that freq is no longer correctly proportional to the amount of air entering this is the reason for needing calibration.

thats my take on it

 

Go to your kitchen and take a pot & lid from under the stove. Take that pot, put lid on it, light the burner. How long does it take for the air to reach 200*F ? Now, after the pot cools to ambient temp, take it and fill it with water. Put the lid on and light the burner. How long does it take to get the water to 200*F?

Don't confuse humidity with evaporation. Humidity is water that is already in the air. Evaporation is the process of getting water into the air.

The major benefit to WI is that you are evaporating water into air thus cooling the intake charge. At the same time you are making the air more humid thus causing the inake charge to be slightly less dense. A brilliant cure for detonation.


Humid air does not cool better. If you are from a dry climate, come visit Houston. If you are from a moderate to high humidity climate, go visit Phoenix.

Remember, the MAF does not measure air flow. It measures a voltage delta across the heating elements.

So, if you are at a steady flow rate (not the same as mass flow), say 50 L/s and we are flowing air at a constant 50*f with 0% humidity. The MAF will output a frequency that corresponds to the voltage delta across the heating elements. If the only variable you change is the humidity, increased to 100%, the MAF will output a lower frequency.

Looking at your MAF table, the lower the MAF frequency, the lower the respective mass airflow rate.

 

Exactly. That's why the carbeurator guys run rich in humid weather. Higher relative humidity, less air.

Yes. The MAF is not an airflow meter like an anemometer. It is only good at determining changes in mass airflow. So then I refer back to my question about latency. Since airflow characteristics can change drastically with a modified engine, does the MAF calibration needs modification to the slope of the curve (vs. actual pinpoint values) to more accurately reflect the sharper deltas?

 

I recently got a copy of How to Understand, Service and Modify Corvette Fuel Injection & Electronic Engine Management (Probst). It has a lot of neat Gen III engine info in it.

According to Probst, the MAF signal adapts to changes in air mass in 1-3 ms.

But maybe not a lot less air.

Relative humidity is the percentage of water vapor in the air vs. the amount the air could hold if it was totally saturated. Looking at this table, the saturated vapor density at 20° C is 23 gm/m^3. Pulling out an old physics text, I see the density for dry air (20° C and 1 atm) is 1.29kg/m^3.

The percentage of mass due to water vapor is when at 100% relative humidity (without correcting for dry vs. wet air) is approximately 0.023/1.29 or 1.8%.

So it seems like the effect of relative humidity on things should be small. But it wil have some effect and I don't see any obvious way for the PCM to find out about it.

 

Exactly!

I would believe the answer to be yes. If you use RHS's spreadsheet to tune the MAF, it should automagically create the new curve.

 

one time i calculated the diff with humidity and the effect on fuel and it was only about 2% from saturated to dry, which most of the time we are in the 50-100% RH range. all i know is after i did it, it was so small i didnt even care about it

 

But if 1-3ms reaction time is correct, then latency is not an issue. Granted you can still recalibrate the MAF, but I still haven't seen the real reason why you should have to. Unless the MAF isn't the real problem.

I still think that the VE must be off if the plugging the MAF back in causes the trims to go awry. Unless everyone is trying to make their tune do something that closed loop MAF operation won't allow with the stock MAF calibration. e.g. run too rich, which would conflict with setting target AFR to 14.7.

My head is getting foggy now...bear with me.

 

The MAF isn't the real problem.

The harmonic (for lack of a better term) properties of the motor change when you swap the cam, heads, manifolds, headers, etc...

 

I can believe that the MAF on a flow bench would be very accurate vs. on an engine.

I will say this. My car was running on the original dyno tune (trims disabled) and it ran ok. I turned on the trims and tweaked the VE and driveability is much better on idle and off. WOT is still great too. Maybe my approach just fools the computer from the other end..?

 

you can have just about everything mistuned, as long as you got MAF and IFR right, your WOT can be pretty damn solid. and the fact that it will run like *** drivabiltywise is apparently of no concern to most 'oldschool' tuners.

 

What kind of beer do you like?

 

haha, couldnt have put it better myself

 

I can't imagine tuning for a living. I spend hours tweaking every last detail so that the car drives like perfect. I'd lose money.

 

not to hijack anything but...
do you charge people when you do stuff for them? i don't, simply because
a) i don't feel like i know too much, i'm still learning/experimenting on their hardware
b) how could i charge them? by the hour? then i'd probably need close to 15-20hrs on a car to do it right (initial settings are like an hour, VE is usually 3-4 rides, MAF is another 2-3, timing/PE can take forever to do right too, then you need cold idle adjustments, do it twice for automatics) so by then i'd have to charge them probably a cool grand, which noone is gonna pay in the world of 250dollar 'mail tunes' and 500dollar 'dyno tunes'.
the problem is i know my **** runs better/smoother/easier/more efficient/less abrasive, but good luck explaining it to someone that doesn't know why mail and psuedo dyno tunes are complete bogus. and on the inverse, if they do know it, then they're probably already tuning themselves, at which point you end up with no clientele.

the only way to make any money off this is to offer 'basic tune', stuff like PE that doesn't smell like bacon, more than 19degs of timing for 01-02 cars, nicer shiftpoints for auto trans, deleting some codes and maybe a speedo/gears calibration. the moment you get into riding around scanning stuff, it becomes long hours, and some people don't feel comfortable beating on their car (ie. high rpm VE tuning) for extensive periods of time, others just are afraid of tickets (ie. high frequency MAF tuning).

sorry, but this been just bugging me for a while, as i spent another 2 days tuning one car and i still don't consider it done, even though it's in much better shape than before.

 

If you tune enough cars, you can acquire enough files to get a car 95-98% dialed in within 5-10 minutes (basic tune). Then spend an hour or two to tweak the rest.

I don't charge, because no one has ever asked me to tune their car.
If someone did, I'd have to at least charge $100 for the extra license.

 

RHS - interesting twist of topic.

when it comes to other peoples vehicles, i'm not for hire. I'll help out a friend when ever I can, but when you start charging, it's no longer a hobby - it's an endless commitment.

 

Okocim Porter

seriously though, haven't you 'taken apart' a 'pro/dyno' tune yourself? messed up IFR, untouched MAF/VE/RAF, timing jacked up like a toddler on jolt cola, knock everywhere, trims so out of wack that computer refuses to learn, etc.

i wish i had a picture of IceT doing the Playaz Haterz Ball from the Chapelle Show, it would be perfect: hate, hate, hate...

 

Why yes I have. I had a sponsor do my first tune. Put down good numbers, but it wouldn't idle or drive on the street worth a ****. I was told the only way to get my cam to idle would be at 1100 rpm... And the explaination for all the bucking, surging, and hopping "Welcome to Big Cams"

I picked up a copy of Live, started searching this forum, and almost **** when I saw what the "pro" did for a tune. MAF table arbitrarily scaled 5%, IFR not even close, basic scale down on the VE to try and get the 1100 rpm idle, displacement param off by ~30 CI, etc...

I don't have new dyno numbers to view the results of my tuning efforts (will have them in the next month or so), but the SOTP dyno doesn't lie Part throttle is neck snaping and WOT will flatten your stomach against your spine. And Idle, 825 RPM with stock manners (ignore the lope).

Knowing what I know now, I can't see why anyone would want to $400-$500 on a pro tune when you can get HPT or EFILive for a few bucks more...

Next time you're in Houston, or I'm in Naperville, I'll get you that beer

 

Just curious, what size cam?