Humidity spark tables

[ShaneB]

Anyone know the ratio of relative humidity to the humidity spark multiplier table? It only goes from 0 to 4.0%, which clearly isn't a 1 top 1 scale with relative humidity, and can take away up to 2.4* and add up to 1.3* with the current values in my tune. Is that much control necessary and needed, or is it okay to set that table to 0, or perhaps even just lower it so it only has a 1* effect plus or minus? Any help would be appreciated, trying to get my flex timing dialed in, doesn't help when 1 day it'll peak at 26*, and the next 28.5* with nothing else changing modifier wise and just a slight change in the weather

[tjd1991]

I zero it out and I think most people do. I don?t want anything adding advance for me

[HeavyChevy305]

I zero it out and I think most people do. I don?t want anything adding advance for me

+1

[ShaneB]

do you make any adjustments to the base table to compensate for the humidity modifier no longer pulling spark?

[ShaneB]

Anyone? It seems like usually these tables are pulling 2* or so all across the board, wouldn't you want to adjust the base table if you zeroed them out so you don't have timing before MBT?

[HeavyChevy305]

It's just one less table (multiplier) you have to worry about when you're trying to get what you want out of the main High Octane table.

[ShaneB]

Right, but i feel like from factory the base tables are made with having all modifiers in mind. Shouldn't I compensate in one direction or the other as a starting point since I'm removing one of them , or no?

[HeavyChevy305]

The High Octane base table more or less has the timing set where the car makes best power in ideal conditions. High IAT, ECT, humidity etc. pull timing for "safety".

What vehicle are you calibrating?

[ShaneB]

Fair enough. Im running E85 full time anyways so its already nice and safe. Tuning my 18 Camaro 1LE

[HeavyChevy305]

Fair enough. Im running E85 full time anyways so its already nice and safe. Tuning my 18 Camaro 1LE

Invest in a flex fuel sensor. What comes out of the pumps is never 85%. You probably have your Stoich set too rich for what's really in your tank.

[ShaneB]

Invest in a flex fuel sensor. What comes out of the pumps is never 85%. You probably have your Stoich set too rich for what's really in your tank.

If you re-read the first post, you'll see I said "flex"

[TriPinTaZ]

Sorry to drag up an old thread but this topic is not widely discussed on here.

I never zero the humidity tables but I do modify them. The humidity has a direct effect on combustion speed. More humid air needs more timing than less humid air. Essentially if you tune the car for maximum timing in humid air, you may be beyond MBT or Knock Resistance when the humidity drops and the air is cold during winter months. If you tune the car for maximum timing in cold weather and low humidity, you will be leaving power on the table when summer comes along and the air is humid again.


https://asmedigitalcollection.asme.o...nd-Humidity-on

[15ltz6.2]

So what’s your thoughts here gm has already figured it out so leave it stock? I’m curious to this as well.

[TriPinTaZ]

Depending on the car and mods, I either leave it stock or I modify it a little bit so that it wont pull as much timing in the peak torque area. I know many tuners zero it out because they want the car to always provide the timing that is demanded. This may make sense for a race car or track car that is constantly tweaked and monitored. But for a daily driver car where the owner doesn't look at anything it is the wrong move in my opinion.

If you're tuning in the cold and the air is dry, then you just need to know when it gets humid again the car is going to put more timing back in it with the humidity tables and vice versa if you're tuning when its humid. From what I can tell the humidity multiplier columns that go from 0.0 to 4.0 is actually just 0% to 400%. Obviously you will never see anything over 100% humidity so the first 4 rows (0.0-1.5) which is 0% to 150% would be the only cells ever used. The way I figured this out is say you are commanding 25 degrees of timing, but you're only getting 24. Humidity is 60% or so. Looking at the multiplier, that would land somewhere around a -0.50 on the interpolation area between the 3rd and 4th row. Then you look at the humidity table and you see that it has 2 degrees in that area. 0.50 x 2 = 1 degree. There is your missing degree of timing.

So if you tune based on knowing where the humidity multiplier will be operating than you can still tune the car to safely have the most timing it can use when its humid/warm and the same for when its dry/cold. It really only deviates a little bit. When its humid out the multiplier is usually around -.40 to -.50. When it gets cold and dry out the multiplier changes to about -.70 to -.80. When you are looking at 1,2 or maybe 3 degrees max in the humidity tables that isn't a large deviation. Often I will lower any values over 2 in the humidity table to 2 in the WOT area. That way I can still tune the spark curve and know that I could have -0.75 to -1.5 degrees depending on weather for the WOT operation. The part throttle stuff I don't worry about.

Now if you're tuning a race car then it probably isn't worth messing with any of this because you will be adjusting the tune for weather every time you go to the track anyhow.

[eficalibrator]

The people who just zero out tables like this don't understand how combustion works.

There, I said it.

GM engineers understand the physics behind combustion in their engines. Among the many things going on, flame speed and knock resistance are affected by the (small) amount of water (vapor) present in the combustion chamber. The effect is not huge, but it's there. As engine controls have gotten more and more precise, small effects like this are now possible to account for in the control system, so they added the function and populated it based on measured data in their development dyno cells.

Zeroing out the table does not change the physics of what's going on under the hood, it just ignores it.

Even on the supercharged GenV applications I've worked on (that had to pass emissions and meet warranty standards in addition to making power), I've always kept these tables in there. There are plenty of other tables to add/remove spark advance if you wish without undoing the good work in this one. At most, we'd just run a SLIGHTLY lower multiplier against it, but I don't recommend throwing it away completely if you want an engine that is truly optimized.

[sevinn]

I wish we had access to the reference values to tell the car the condition the car was calibrated in.

[TriPinTaZ]

The best you can do is log the humidity PID's but I don't know how accurate they are. I THINK specific humidity is the value that is used for the humidity spark multiplier. The values are not exact but they are close. So I feel like there is something else at play here that we can't see such as a temp multiplier too which would affect relative humidity vs specific humidity.

[eficalibrator]

Relative and Specific Humidity Explained

If you look at the Humidity Spark Multiplier table in a stock truck calibration, you can see that have a dead zone where the multiplier is zero. Below that, the multiplier gets progressively negative (less total spark delivered to engine) in drier air or progressively positive (more spark added) in humid conditions. This follows the physics of what happens as more or less water is introduced into the combustion chamber during the burn. It's just physics, and the burn rate moves whether you zero out the Humidity spark tables or not. I would suggest leaving this alone and concentrating your tuning efforts elsewhere.

[sevinn]

Relative and Specific Humidity Explained

If you look at the Humidity Spark Multiplier table in a stock truck calibration, you can see that have a dead zone where the multiplier is zero. Below that, the multiplier gets progressively negative (less total spark delivered to engine) in drier air or progressively positive (more spark added) in humid conditions. This follows the physics of what happens as more or less water is introduced into the combustion chamber during the burn. It's just physics, and the burn rate moves whether you zero out the Humidity spark tables or not. I would suggest leaving this alone and concentrating your tuning efforts elsewhere.

I guess I don't know what I was worried about with the reference values. If you tune it on a humid day and you're happy with your final timing sobeit, the table will do the work when it dries out and vice versa.

[TriPinTaZ]

Relative and Specific Humidity Explained

If you look at the Humidity Spark Multiplier table in a stock truck calibration, you can see that have a dead zone where the multiplier is zero. Below that, the multiplier gets progressively negative (less total spark delivered to engine) in drier air or progressively positive (more spark added) in humid conditions. This follows the physics of what happens as more or less water is introduced into the combustion chamber during the burn. It's just physics, and the burn rate moves whether you zero out the Humidity spark tables or not. I would suggest leaving this alone and concentrating your tuning efforts elsewhere.

I think the concern some of us has is that the multiplier values don't seem to correlate to reality. On most Gen V LT4's I tune, the multiplier column axis goes from 0.0-4.0 %. On these cars I have NEVER seen the the car ADD humidity spark, rather it just subtracts less in humid weather and more in dry weather. It would be nice to know for sure what the 0.0-4.0 column axis actually references. I am assuming it is 0-400% humidity.