[Mike@N54Tuning.com]

Originally Posted by Ilma

But I know the point you are trying to illustrate....that throttle
closure can be directly correlated to boost targets being exceeded.

Really the DME boost target and DME boost are critical in any analysis. They should always be included in every log. Much more relevant than throttle position when talking about boost targeting effectiveness, IMO. Also, by studying them, you can learn a lot about how the factory DME behaves. A DME boost too far below the DME target indicates the piggyback is leaving too much slack in the system and is unsafe. They should be very close together as much as possible.

Mike

[Mike@N54Tuning.com]

Originally Posted by jpsimon

*my latest logs were at ~80f, 70% humidity

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

[Sniz]

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

seriously?

[Mike@N54Tuning.com]

Originally Posted by Sniz

seriously?

It is a trick of the trade.

Mike

[jpsimon]

Michael, the logs I posted were a work in progress (not optimal yet, have more logging to do), I was simply demonstrating that timing can be changed and not "learned out" as Terry/you claim.

I'll post more logs demonstrating this as soon as I get my car back.

[hotrod182]

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

Ha, I knew these guys in Florida with high humidity and 90F had an advantage over our dry 100F temps at California drag strips right now.

[OpenFlash]

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

[hotrod182]

How does humidity affect knock? I would assume that higher humidity content has different thermal absorption properties than dry air. Not talking about oxygen content and horsepower potential, just knock resistance properties.

[scalbert]

Originally Posted by hotrod182

How does humidity affect knock? I would assume that higher humidity content has different thermal absorption properties that dry air. Not talking about oxygen content and horsepower potential, just knock resistance properties.

Higher humidity does lower the octane requirements. However, the displacement of O2 and the fact of the higher heat retention often means the lower octane requirement is lost to the offset of the heat retention and less O2 density.

The best air is cool and dry. The worst air is hot and humid. As humidity increases, the effective air pressure decreases.

[scalbert]

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

Shouldn't that be a wink as that is so far from the truth.

H2O injection is primarily beneficial due to the heat absorption from the quick evaporation of the water. High RH is already a vapor and does not provide a cooling effect. If anything, it increases heat retention.

[jpsimon]

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.

Mike

That has "truthiness" written all over it

[Mike@N54Tuning.com]

Originally Posted by shiv@vishnu

http://www.repairfaq.org/filipg/AUTO/F_Gasoline8.html

Mike

[scalbert]

Originally Posted by Mike@N54Tuning.com

http://www.repairfaq.org/filipg/AUTO/F_Gasoline8.html

Mike

Don't just link, expand and provide information. As I stated, yes, higher humidity does reduce the octane requirements. But that article does not suggest high humidity and water injection do the same thing. There are far too many negatives, which generally outweigh the octane requirement reduction, in high humidity; for instance, the greater heat abortion and retention, etc.

Water injection’s greatest benefit is that process of conversion to a vapor. This takes quite a bit of energy and that energy comes from the air. That reduces the air temperature. High humidity has already undergone that process and quite often, has absorbed additional heat in the movement across the earth.

[hotrod182]

Originally Posted by scalbert

Shouldn't that be a wink as that is so far from the truth.

H2O injection is primarily beneficial due to the heat absorption from the quick evaporation of the water. High RH is already a vapor and does not provide a cooling effect. If anything, it increases heat retention.

That is correct, heat of evaporation is what brings benefits with H20. What you are saying is true if air is saturated with high RH at 95F ambient, and discussed engine operating temps remain at those temps. But what happens to that saturation level when temps are raised considerably? (such as in your intake tract at temps approaching 170F after the intercooler!). The air at those temps is no longer saturated with water vapor, and there would be benefit from the evaporation effect. Warmer temps will support more evaporation.

[brianhn1]

Originally Posted by hotrod182

That is correct, heat of evaporation is what brings benefits with H20. What you are saying is true if air is saturated with high RH at 95F ambient, and discussed engine operating temps remain at those temps. But what happens to that saturation level when temps are raised considerably? (such as in your intake tract at temps approaching 170F after the intercooler!). The air at those temps is no longer saturated with water vapor, and there would be benefit from the evaporation effect. Warmer temps will support more evaporation.

You're right. But it is more obvious than that. As you increase the pressure of water vapor very quickly as in does in the engine, it turns into superheated liquid water. Refer to the phase diagram of water. As the ignition occurs, the liquid water turns back into vapor thereby decreasing the overall combustion temperature, exhaust gas temperature, reduce tendency to knock, etc. However, humidity/water generally reduces power because it does decreases the temperature away from which optimal combustion (most efficient) occurs and does not have a cooling effect to reduce the temperature of air coming into the engine (unable to increase density of air).

[lawdude]

Originally Posted by Mike@N54Tuning.com

JP, please don't take offense to this, but we're trying to keep this as a technical thread.

No offense, but technical lasts until credibility vanishes.

[nj1266]

Mike,

Are the timing traces of the first two charts logged from the OBDII port?

[Mike@N54Tuning.com]

Originally Posted by brianhn1

You're right. But it is more obvious than that. As you increase the pressure of water vapor very quickly as in does in the engine, it turns into superheated liquid water. Refer to the phase diagram of water. As the ignition occurs, the liquid water turns back into vapor thereby decreasing the overall combustion temperature, exhaust gas temperature, reduce tendency to knock, etc. However, humidity/water generally reduces power because it does decreases the temperature away from which optimal combustion (most efficient) occurs and does not have a cooling effect to reduce the temperature of air coming into the engine (unable to increase density of air).

This is a bit of a departure from the thread, but funny that Shiv and Steve want to dig their heels in to the ground and fight about what was essentially a funny comment. The water reduces combustion temps and thus lowers the octane requirements. At the same time it reduces power, due to those lower combustion temperatures, and that oxygen has been displaced by the water. A small amount of water can make a big difference though as evidenced by water injection systems. All tuners know this and setup dyno testing with it to their advantage. Dry air on race gas, higher humidity on pump gas.

Mike

[Mike@N54Tuning.com]

Originally Posted by scalbert

Don't just link, expand and provide information. As I stated, yes, higher humidity does reduce the octane requirements. But that article does not suggest high humidity and water injection do the same thing. There are far too many negatives, which generally outweigh the octane requirement reduction, in high humidity; for instance, the greater heat abortion and retention, etc.

Water injection’s greatest benefit is that process of conversion to a vapor. This takes quite a bit of energy and that energy comes from the air. That reduces the air temperature. High humidity has already undergone that process and quite often, has absorbed additional heat in the movement across the earth.

From the article..

7.12) What is the effect of humidity?
An increase of absolute humidity of 1.0 g water/kg of dry air lowers the octane requirement of an engine by 0.25 - 0.32 MON [27,28,38]."

-------

It is simply common knowledge that high humidity stabilizes timing values and reduces the octane requirement to a degree. I don't think anyone suggested driving around in 70% humidity is like strapping on a 10 GPH water injection kit

Mike

[brianhn1]

Originally Posted by Mike@N54Tuning.com

This is a bit of a departure from the thread, but funny that Shiv and Steve want to dig their heels in to the ground and fight about what was essentially a funny comment. The water reduces combustion temps and thus lowers the octane requirements. At the same time it reduces power, due to those lower combustion temperatures, and that oxygen has been displaced by the water. A small amount of water can make a big difference though as evidenced by water injection systems. All tuners know this and setup dyno testing with it to their advantage. Dry air on race gas, higher humidity on pump gas.

Mike

More fuel to defeat, the issue of high humidity recently has been a highly studied issue in engine management. With the EPA mandating lower CO2 emission requirements these coming years, manufacturers are developing more powerful catalyst converters that require EGT to be above a certain threshold for optimal effectiveness. Under high humidity conditions, the engine will either lean the fuel mixture or retard the timing further under low load conditions to compensate for the reduced EGTs. Obviously our N54s don't have a humidity sensor so this sort of logic is not implemented. We will definitely see it in newer cars.

[Mike@N54Tuning.com]

Originally Posted by nj1266

Mike,

Are the timing traces of the first two charts logged from the OBDII port?

Using a BT cable..

Mike

[scalbert]

Originally Posted by Mike@N54Tuning.com

This is a bit of a departure from the thread, but funny that Shiv and Steve want to dig their heels in to the ground and fight about what was essentially a funny comment.

No digging but the below was a stretch.

Originally Posted by Mike@N54Tuning.com

That makes sense, high humidity stabilizes timing values. It is like a mini built in water injection.