RomRaider

Just wanted to create a new thread for further discussion of Speed Density and IAT comps on the CarBerry rom.

I finished the Intake air temp load compensation excel spreadsheet based off your post in the other thread that contained the picture below.





The Url is https://docs.google.com/spreadsheet/ccc?key=0ArVsTZNIbIEtdFpmdV80cVNFQ2dXeU1nYUR3emFRS0E&hl=en_US#gid=0

Everything has been calculated by using the dry air density calculation P = R /T
Where
P=Air Density
R=Partial Dry Air Pressure
T=Temp in Kelvin

Please do not change anything other than what is in white, I worked hard on this.

Note: The values have been corrected for this rom.

If the math is that straightforward, why not make tables for the "white" parameters, and let the ECU calculate the rest?

Or do that plus keep the table, but fill the table with 0s by default. Then you could use the table if there's something going on with a particular setup that can't be tuned any other way.

I suppose you could make the ecu calculate this, but you may as well leave these values on default and adjust if need be instead of zeroing them out while keeping the values in memory.

Im going to whip up a quick experimental ROM with the 3D IAT table. Anybody that wants to test it out shoot me a PM and ill send it to you

If it works well I can look into having the ECU do the calculations. But the values do look a little extreme in some areas, remember that the min/max compensation is 0.0000/2.0000. I cant imagine that 100% or more fuel would need to be added as the chart suggests in some areas.

I really should have said "leave them at 1.0" rather than "leave them at 0."

I'm guessing it will only take a couple of CPU instructions to have the ECU account for IAT in the same way that the ideal gas law describes. The table could then be filled with 1.0, so that when working with this table you'd only need to think about how much you're deviating from the gas law, rather than having to do the gas law math plus figuring out how much to deviate from it.

I understand the need to take temperature into account, since it affects density, I'm just suspicious of the need to deviate from the ideal gas law with a 3D table. I'd like to think that the ideal gas law doesn't depend on manifold pressure or engine speed. Creating an IAT compensation table like this one is basically equivalent to saying that one of the fundamental the laws of physics doesn't hold true in a uniform way at all manifold pressures and engine speeds. If that turns out to be the case, we should really figure out what's going on.

If the table's default state is 1.0 in every cell, with the ECU doing the basic gas-law compensation, then:

a) People will be less tempted to tweak this table. If the gas law math works (and I think that it mostly will), then VE table should be sufficient for almost everything, so it would be better to steer peoples' attention to the VE table.

b) When people do tweak this table, it will be obvious where they've deviated from the normal values, and by how much. That will make it easier to recognize patterns in the changes people are making, and that will make it easier to figure out what's necessitating the changes.

I'm a big believer in physics. If the universe won't obey the laws of physics, then I want to understand why.

Besides "static gas law" do not forget dynamics.
IAT corrections needed may follow the Gas Law at full throttle\low RPM but at low load OR high RPM they are much less.

Just compare a pair of VE summer\winter or underhood\cold air intake calibrated.

Have you read the last couple of pages of the SD thread that kind of started all of this? viewtopic.php?f=26&t=7594&start=810
Maybe you can take a look and give your opinion on what the multiplier and offset are. IMO, the multliplier is air density, I thought you needed air density to calculate airflow. And the offset is some correction, maybe for the Group N restrictor plate...
Carbibbles thinks it is the slope of the map and load.
I think mrf582 just likes to argue, but he proofed the IAT comp table in the ROM, he just screwed up the percent difference calculation and got some wrong numbers. Fix the formula (new/old) and you get the same comps as the ROM.

^^^ The multiplier and offset are a linear equation to get engine load from manifold pressure. I can prove this in any way you would like, just let me know what evidence you would like to see.

As further proof, I run a multiplier of .09 and my car runs fantastic. I doubt the air is almost 30% more dense in my area.

would you mind posting a log of cruise at some temp and another at 20+ or 20- degrees.
Need st trim, lt trim, fuel final base, injector pulsewidth, injector deadtime, stock afr sensor, rpm, map absolute, cl/ol, engine load, IAT.
also post your iat comp table and injector scalar. Thanks Carbibbles.

Carbibbles, did you put .09 in all the cells?

@bcheck - My car is down at the moment, I blew 3rd gear. I can get some logs when I get the new trans in. you could see if Lukesky could post some logs, I believe he runs a multiplier of 0.1




.09 for the SD multiplier, not the iat comps. I run the standard iat comps

Ouch sorry man, that sucks.

If anyone can post logs with requirements posted a few posts up, I'd appreciate it. Thanks.

That's very true but how often do you think you'll be hitting most of those? If my car was running I would gladly test out this 3d IAT compensation map, however that's hard to do with the engine out of the car.

I agree with you also though about possibly having to add 100% fuel in some spots, just wouldn't make sense. I think it would affect it more at low load and cruising than at high rpms or high boost.

Did some logging today 10 degrees difference, is this even possible?