Load tuning/temp relationship

[laxplayermjd]

So ive been spending alot of time reading all the tune threads on MSF. There is alot of boost tuning threads now, but i keep seeing one thing mentioned. they all plan to have two maps one for cold and one for warm weather. Seems like alot of effort and room for error. They claim this is still better than load tuning but i dont understand why they say this. Something about targeting load in different weather keeps power down. I think many think its too hard to tune smooth boost curves using load tuning.

From my understanding with stock ecu logic of targeting load. It doesnt matter what temperature it is, for ex targeting a load of 2.0 when its 90 degrees vs say 40 degrees. The main difference would be higher boost in the 90s and less in the 40s. But since the loads are the same the "power" should still be the same. The calculated load is pretty much direct correlation to torque of the motor correct?

As far as the temp changes the ecu still uses the same logic to calculate the load, and the only changes would be something like a table to reduce wgdc with temps?
Or due the ecu possibly change load values with temp changes.

Then again you could say power is more related to maf g/s or volts which you would see higher values due to the colder temps, but then again you be at a lower boost level so youll have less again.

Just trying to wrap my head around all this tuning stuff. I could be completely wrong or still missing some understanding and info.

[fez]

And that is why I don't try to tune myself! hahaha

Definitely interested in what you guys have to say about this. MSF fanboys are definitely into boost tuning and most believe that load tuning is useless.

[06Speed6]

You boost tune because its simpler to tune because it doesnt take into account alot of environmental factors that load tuning does account for. Thats why they need to retune every time the temp or elevation changes.

[Ugnius @ VersaTune]

People are often confused by what exactly absolute load is and how it is measured. It is not some kind of mystical property of "how hard the engine is working", since "hardness" is not directly measureable by the ECU.
ISO standards give a unified standardized definition of absolute load value that is the same across all spark ignition cars. I'm going to post it below and hopefully it clarifies things a little:
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LOAD_ABS is the normalized value of air mass per intake stroke displayed as a percent:
LOAD_ABS = [air mass (g/intake stroke)] / [1.184 (g/litre) * cylinder displacement (litres / intake stroke)]

NOTE: At engine off and ingition on the LOAD_ABS = 0%

Derivation:
- air mass (g/intake stroke) = [total engine air mass (g/sec)] / [rpm (revs/min) * (1 min/60 sec) * (1/2 # of cylinders (intake strokes / rev)];
- LOAD_ABS = [air mass (g/intake stroke)] / [maximum air mass (g/intake stroke) at WOT@STP at 100% volumetric efficiency] * 100 %

Where:
- STP = Standard Temperature and Pressure = 25 degrees C, 29.92 in Hg (101.3 kPa) BARO, WOT = wide open throttle
- The quantity (maximum air mass (g/intake stroke) at WOT@STP at 100% volumetric efficiency) is a constant for a given cylinder swept volume. The constant is 1.184 (g/litre) * cylinder displacement (litres/intake stroke) based on air density at STP.

Characteristics of LOAD_ABS:
- ranges from 0% to approximately 95% for naturally aspirated engines, 0% to 400% for boosted engines;
- linearly correlated with engine indicated and brake torque;
- often used to schedule spark and EGR rates;
- peak value of LOAD_ABS correlates with volumetric efficiency at WOT;
- indicates the pumping efficiency of the engine for diagnostic purposes;

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So basically absolute load is nothing more but the ratio of air mass actually entering the cylinder in comparison to the air mass of a static cylinder at standard temperature and pressure.
Naturally aspirated engines work at atmospheric pressure, so the mass of air that the cylinder can suck in is limited by volumetric efficiency of the engine, that's why load never exceeds 1.0 there. Turbocharged engines have turbos to help squeeze in more air. When you see a load of 2.0, it means that your engine is pumping twice as much air as it would pump being a NA engine working at 100% volumetric efficiency.
It is correlated to torque, hence the notion of "how hard the engine is working".

When you target specific absolute load, you're basically requesting specific air mass per intake stroke. Since load is targeted in a closed loop fashion (don't confuse with engine operating mode - it can be both open loop and closed loop), ECU will keep adjusting throttle and boost until it hits the target load, i.e. airflow, regardless of environmental conditions.
There are tables in the ECU that limit the desired/maximum load under different conditions, such as current gear, barometric pressure, knock/no knock, overload etc. So the desired load may be lower depending on the weather. But ECU will always do all it can to match actual load to desired load.

[fez]

Whoa. This is interesting. Thank you for the post!

So Load based tuning is safer and smarter as you essentially let ECU do what it was made to do. HA! But it's harder to make high power this way, correct?

[laxplayermjd]

now in sratching my head haha. So since its basically air mass, the same load values at different temps are pretty much equal then?

I guess say you dyno at 40 degrees and one at 90 degrees with the same map. Are they going to be similar numbers?

[Ugnius @ VersaTune]

Same load values mean same mass air flow at given RPMs. Dynoing at 40 and 90 degrees and hitting similar loads should produce similar power numbers, but there are other factors that determine power apart from airflow.
Firstly, the ECU is not always able to achieve desired load (it can't raise boost, if it's already running 100% BCS DC, if the BATs go high, it will pull timing, etc.). So dynoing with the same tune in different conditions can show different absolute loads. It has compensation tables that will make it proactively target lower load in dangerous conditions.
And even if loads (and airflow values) are similar, power also depends on other factors like AFR, fuel atomization quality, ignition timing, cylinder temps and so on.

[laxplayermjd]

yea after i posted i realized it would still depend on boost temps, since timing will be most affected by that.

The best thing would be load tune in summer months and you should be pretty similar year round. Like my map now is about 90%wgdc in the heat. I think that would be optimum to develop you tune in summer months , then log and monitor in the winter when you may see my spiking and may need to make minor changes to the load error table.

But generally in still not getting how boost tuning is better than load. Besides that some may just find it easier and then make summer and winter map

[Ugnius @ VersaTune]

I guess it's easier to keep the turbo in its max efficiency range with boost tuning. With load based tuning you don't have any guarantees as to what the boost pressure will be. On the other hand, you get consistent performance all year round and in all elevations.
Maybe Steve can chime in, he has experience in both areas.

[Steve @ VersaTune]

Load target tuning done right will give more consistent power. That's why OEMs use it.

With boost target tuning, if you tune for x kPa, then you will make more power when it's cold and less when it's hot.

What you need to do is decide up front how much cylinder pressure (torque) your engine can handle and how much torque your driveline can handle. Then tune for that load target in all conditions. Just because it's cold out and you could make more power doesn't necessarily mean that you want to if it will break parts.


I think the main problem is that people directly associate boost pressure with power. Without taking temperature and exhaust back pressure into account, boost pressure alone can not tell you how much power you are making or will make.