Bandimere 4/20

[LittleBlueGT]

I find it hard to believe that heatsoak would be a problem on a dragstrip run like this. While I can fully believe that air flow into the hood scoop is affected by speeds above 100 (air flow is probably actually skipping over the scoop opening at that speed), I can't believe that heatsoak would be able to set in within 12 seconds of starting boost - it just doesn't seem plausible. I agree with Legend that timing seems like a bigger concern.

 

But the timing is run in 3rd no problem, and it is not just pulling a couple degrees, it is pulling a crap ton load!

 

Trust me, with no airflow all it takes is 2 or 3 seconds and the post TMIC air temps will go waaaay up.

[LittleBlueGT]

Did you ever log AFRs when this happens?

[Legend]

NSFW - I'll plug my tables into Timing Editor when I get a chance.. I know the timing maps in relevant cells are smooth, however, and the loads in the 4th are just about the same as the loads in 3rd.

 

LBGT - No, I wish I logged AFR's. I keep a bung in the DP and have the WB02 in the engine bay... it would have just taken 2 minutes to pull the bung and insert the WB02 and I really wish I would have done that. I am missing key information without that data and would be nice to know if fueling is playing any role.

 

From the one and only (above posted) log that I have of this phenomenon, I plotted MAFg/s vs. gear for the dragstrip run. Somewhat interesting. But first, I must say that the relationship b/w MAFg/s and whp is NOT directly proportional, at least in my car. As evidence of that assertion, from my dyno experience I did a high boost pull with MAF g/s peaking around 318g/s, then a lower boost pull with MAFg/s peaking around 312g/s and the lower g/s pull made 3-5whp more than the higher boost pull. Anyways, here is MAF g/s vs. gear...

 

http://beeez.com/lgt/mafgs.jpg

 

What's interesting is that 4th gear was theoretically benefiting from running my regular amount of timing while 2nd and 3rd were pretty handicapped from FBKC... yet 4th gear made less g/s than 2nd and 3rd... here is the timing data from the same run again... (sorry, the graph colors don't correspond)

 

http://beeez.com/lgt/timinghell.jpg

[rao]

But first, I must say that the relationship b/w MAFg/s and whp is NOT directly proportional, at least in my car. As evidence of that assertion, from my dyno experience I did a high boost pull with MAF g/s peaking around 318g/s, then a lower boost pull with MAFg/s peaking around 312g/s and the lower g/s pull made 3-5whp more than the higher boost pull.

 

HERESEY!11!!!!1111!!!

[mwiener2]

Whoa Whoa Whoa... The stock sensors can't be used to calculate power accurately? But then how does an Airboy work?

[LittleBlueGT]

Can you just briefly (I can to, but I am lazy today) plot out psi per gear to compare with the other plots?

 

FWIW once I get close to the max of a medium sized turbo I usually notice power fall a bit for the last few g/s (like the last 10).

 

I never really tune big stuff, but I am doing a GTX3076 next month, and I guess that is at least as big as an old GT35R, so I don't know what to say about bigger turbos, cept we won't be pushing it much, probably just 22 psi as it will only be on pump gas.

[LittleBlueGT]

I forgot that you are consuming a lot of oil. Maybe there is a chance that that oil is finding its way into your engine, can causing the det?

[Legend]

Can you just briefly (I can to, but I am lazy today) plot out psi per gear to compare with the other plots?

 

http://beeez.com/lgt/boost1243.jpg

 

Sure.. finally some real pretty data.

[Legend]

Time spent in each gear on this run:

 

2nd gear: 2.88s

3rd gear: 3.60s

4th gear: 4.46s (or 4.02s when chaos hits)

 

Wonder if that is a factor?

[LittleBlueGT]

http://beeez.com/lgt/boost1243.jpg

 

Sure.. finally some real pretty data.

 

nice boost control.

 

Would a hotter TMIC cause more of a restriction causing less airflow at the same psi? I think so, as the hotter air presents more of a restriction to the motor. If the TMIC is cooling the air, then it is more dense, and should likewise help with airflow, hotter air throughout the whole TMIC would do the opposite I think.

[mwiener2]

Hot air flows better than cold air. But the difference from 100 degree air to 300 degree is pretty negligible.

[LittleBlueGT]

Hot air flows better than cold air. But the difference from 100 degree air to 300 degree is pretty negligible.

 

That statement is true on its own, but in a restricted area under pressure I am not so sure.

 

Notice how tires will show higher pressure when they are warm? Well the higher pressure in the TMIC may have contributed to lower overall airflow, as (all things being equal) the boost may have been higher to achieve the same airflow, but of course the ECU still had the same target boost, hence the lower airflow.

 

Airflow @ 100F @ X psi = Y

Airflow @ 300F @ X psi = .95Y

 

Maybe....................

[Legend]

Hot air flows better than cold air. But the difference from 100 degree air to 300 degree is pretty negligible.

 

Bringing your HVAC background into play, I see.

[mwiener2]

Pressure in tires goes up because the air is heated. The compressed air is hot because it was compressed. When you move outside a compressor efficiency range, more energy goes into heating the air rather than compressing it.

 

100 degree air at 10 psi has more oxygen molecules in it then 300 degree air at 10psi. That's why colder air = more power.

[LittleBlueGT]

Pressure in tires goes up because the air is heated. The compressed air is hot because it was compressed. When you move outside a compressor efficiency range, more energy goes into heating the air rather than compressing it.

 

100 degree air at 10 psi has more oxygen molecules in it then 300 degree air at 10psi. That's why colder air = more power.

 

 

And your point is? How does this data support your thought process? Why is there less air going in at the same psi in 4th gear? Why do you say things that we all know we both know?

 

 

If the turbo is pumping X amount of pressure into the intact tract, but less actual air is entering, to me that supports the theory I proposed above.

 

to re-cap:

 

-TMIC is getting too hot above a certain speed due to lack of airflow (due to hood-scoop not working at triple digit speeds)

-this now hot TMIC is not cooling very well at all

-turbo is pumping in less air then before, but at the same psi (this is due to lack of cooling in TMIC)

 

 

Sure hot air flows better, but that is because there are less actual molecules moving. That is not the case here. This is not an HVAC system in a house, this is a turbo moving a certain amount of air into a pressurized system. So the air flowing through the TMIC now contains the same amount of molecules, but at a hotter temp, this would cause the pressure to increase, but since turbo is being controlled to a set psi, the actual airflow goes down, while the pressure stays the same.

 

Bingo.

[rapture]

damn, little blue gets +2 internet's .

[mwiener2]

And your point is? How does this data support your thought process? Why is there less air going in at the same psi in 4th gear? Why do you say things that we all know we both know?

 

 

There is less air in 4th because EVERYTHING is now HOT. The Intercooler is hot, the engine is hot, the turbo is hot. Because everything is so hot, it doesn't work as efficiently and creates MORE heat. All this hot air causes an increase in flow but not power.

 

This is not a theory. This isn't something car engineers have been stumped on for years.

 

 

If the turbo is pumping X amount of pressure into the intact tract, but less actual air is entering, to me that supports the theory I proposed above.

 

to re-cap:

 

-TMIC is getting too hot above a certain speed due to lack of airflow (due to hood-scoop not working at triple digit speeds)

-this now hot TMIC is not cooling very well at all

-turbo is pumping in less air then before, but at the same psi (this is due to lack of cooling in TMIC)

 

 

Sure hot air flows better, but that is because there are less actual molecules moving. That is not the case here. This is not an HVAC system in a house, this is a turbo moving a certain amount of air into a pressurized system. So the air flowing through the TMIC now contains the same amount of molecules, but at a hotter temp, this would cause the pressure to increase, but since turbo is being controlled to a set psi, the actual airflow goes down, while the pressure stays the same.

 

 

Regardless if it's a house or a turbine, it's the same air.

 

The temperature would not cause the pressure to rise because the increase in pressure is what is causing the increase in temperature. The action of compressing the air is generating heat.

 

The airflow goes UP as the pressure stays the same because you have to move more hot air to acquire the same amount of oxygen as colder air.

 

The real problem here is that you are using G/S to try and measure overall performance.

 

 

 

edit:

 

 

 

Sure hot air flows better, but that is because there are less actual molecules moving. That is not the case here.

 

 

I don't think that is the reason hot air flows better, but regardless, if that were a fact it would be consistent throughout physics. That's like saying, "water doesn't normally burn, but in my car it does."

[NSFW]

I can't figure out what it is that you guys are disagreeing about.

[mwiener2]

I'm basically saying that his understanding of thermodynamics is wrong and it's complicated enough that there isn't a good way to explain it in one post on a internet forum.

 

A closed system means that no air can be added or removed. Our cars are very open systems. Because of this, the basic principals become not so basic anymore.

[mwiener2]

nice boost control.

 

Would a hotter TMIC cause more of a restriction causing less airflow at the same psi? I think so, as the hotter air presents more of a restriction to the motor. If the TMIC is cooling the air, then it is more dense, and should likewise help with airflow, hotter air throughout the whole TMIC would do the opposite I think.

 

Ok, that's what started me off. The internal passages of the intercooler are a restriction to flow. Hotter air will be less restricted than cooler air, but this difference is very minimal in the temp range that we operate in. So as far as we are concerned, the pressure drop due to friction as a result of the interior passages of the intercooler is constant throughout our operating temperature range.

 

One down.

 

That statement is true on its own, but in a restricted area under pressure I am not so sure.

 

Notice how tires will show higher pressure when they are warm? Well the higher pressure in the TMIC may have contributed to lower overall airflow, as (all things being equal) the boost may have been higher to achieve the same airflow, but of course the ECU still had the same target boost, hence the lower airflow.

 

Airflow @ 100F @ X psi = Y

Airflow @ 300F @ X psi = .95Y

 

Maybe....................

 

This is where the confusion really begins. Our systems are not restricted areas, or "closed" systems. They are open. A closed system has a known volume and a known amount of substance in that volume. While we have a known volume (the intake tract) our given substance (air) is free to change it's amount quite easily.

 

This sentence also doesn't make sense, "Well the higher pressure...hence the lower airflow." Pressure and temperature are directly related. Flow is not directly related to either. Which comes to the tire thing..

 

Pressure in tires goes up with temperature because that is a closed system and pressure is directly related to temperature.

 

Which comes back to flow. You can change the pressure and temperature of the intake charge, while having very little effect on flow. This is why a large turbo can make 150 more HP at 15psi than a smaller turbo can at 25psi.

 

 

 

So I guess to sum it all up. The problem is that by 4th gear the air charge is too hot to make good power. A larger intercooler will help alleviate some of the problem, but a larger turbo is a real solution.

[LittleBlueGT]

Mweiner you bring up some good points (all of which I am well aware of) and yes, much is too complex to bring up here.

 

 

No it is not a closed system, but it is not an open one either (like an HVAC in a home, which technically isn't completely open either).

 

There is less air in 4th because EVERYTHING is now HOT. The Intercooler is hot, the engine is hot, the turbo is hot. Because everything is so hot, it doesn't work as efficiently and creates MORE heat. All this hot air causes an increase in flow but not power.

 

You don't get it. I am waaay beyond the normal turbo, heat, efficiency, size thing. I am dealing with a specific issue, and you are not even addressing it, or addressing it all wrong.

 

In 4th gear he flows LESS air, same pressure, but less air.

 

It can't just be as simple as, "EVERYTHING is now HOT. The Intercooler is hot, the engine is hot, the turbo is hot", there is an abrupt change! If it was as simple as you say, it would be a more gradual change as he goes through the gears, but it is not, all gears are pretty normal, then in 4th it suddenly changes. It doesn't just "get hot" in 4th gear, and not in the others.

[NSFW]

I'm basically saying that his understanding of thermodynamics is wrong and it's complicated enough that there isn't a good way to explain it in one post on a internet forum.

 

A closed system means that no air can be added or removed. Our cars are very open systems. Because of this, the basic principals become not so basic anymore.

 

Whatever. I have yet to see either of you post something incorrect or non-obvious so I don't understand the problem here.

[mwiener2]

It's an open system. Refrigerant in a refrigerator or an air conditioner, that's a closed system. The refrigerant never gets used up, it just circulates.

 

We take air from the atmosphere, compress it, then use it in the engine. The air in our system is constantly replenished, it's open.

 

 

The odd readings Legend got tat say he's flowing less in 4th might not be accurate

 

It's possible that something causes the car to calculate it incorrectly. If he has the stock air intake, the frontal pressure on the car might be causing turbulence in the intake. The odd timing he got might have cause flow differences. The fueling might be off and causing flow problems.

 

There's a lot of variables and with my experience with E85, it would take a really hot intercooler to cause a drop in output.

 

Something definitely happened in 4th, but I don't think it was a hot intercooler that caused the knock sensor to go nuts.

[Legend]

A few random thoughts:

 

- When I was at the dyno I had Harvey (The Boost Creep) do 2 pulls from 2nd gear to around 120mph. (I can't believe I forgot about this until now). I had finished my fine tuning/tweaks on his dyno and since I had previously had issues with the car falling on it's face at ~110mph at the dragstrip I wanted to see if my subsequent tuning had cleared that issue up.

 

So we did 2 pulls. The first pull was clean with no issues in 4th gear at 110mph but my logger got locked so we did a 2nd pull. See below. I've also got a log for this pull from 15mph to 120mph. Both the dyno plot and the logs (at home, I can post later) were perfectly fine for both pulls.

 

This was in the shop, on the dyno, with the hood open. Harvey doesn't put fans on TMIC's, unfortunately, so forceful air directed at the TMIC on any of my pulls. Just the standard big fan a few feet in front of the bumper. I'll post that log later. Here is the dyno of a 2-3-4 pull (only 3rd-4th were WOT 30-120mph).

 

http://beeez.com/lgt/dynogears.jpg

 

 

- Surely someone has has a TMIC'd LGT that has trapped greater than 110-112mph. (Hell, I'm racing at 5800'). Anyone know if anyone else has had this issue?

 

- Another thought that I don't think anyone has brought up.. what about air pressure changing underneath the car with increasing speeds? If air pressure underneath the car is increasing, could it be enough to cause backflow or resistance to air entering through the hood scoop... disprupting the regular pressure differential?

[LittleBlueGT]

- Another thought that I don't think anyone has brought up.. what about air pressure changing underneath the car with increasing speeds? If air pressure underneath the car is increasing, could it be enough to cause backflow or resistance to air entering through the hood scoop... disprupting the regular pressure differential?

 

That is exactly what I was thinking.

 

Do you have access, or do you want to buy or borrow some simple pressure sensors? It would take more then about an hr of messing around to see which way the air is flowing at 110+ mph.