I thought UTEC uses the factory knock sensor? Or at least I thought they don't use headphones...

 

53 degrees today and my car ran perfect

No misfiring or stuttering... hmm wonder what the culprit is.

 

could it be crappy winter gas? i know that sounds like a lame excuse but didn't someone post a big thread about that?

 

I hope it is only the winter gas.

But in fact, my A/F ratio does change and it is not perfectly constant

 

This doesn't make any sense. Dense air isn't compressed more. Density is Mass/volume.

A spring opens with 9lbs of pressure, which means that in the cold it will take less volume to open the spring, and in the hot, more air to open it. But the spring rate isn't rated on volume it's opened on weight, and therefore if the cold air weighs more (AGAIN it does not, only in weight per CM3) it would open the WG before it would in warm air.

 

Like I said. I've never heard an answer to this question from someone with a fluid dynamics background. I already stated this is just what I have been told. I already know it may not be true and stipulated that.

 

Ok, I'm ruling out the gasoline theory.

It did it again with a new tank of gas but it only happens

when the temperature is around 40F degrees according to my car.

 

Also, it only happens when the A/F ratio is above 11.5~ish

Is that not enough information to come to a conclusion?

 

It's not fluid dynamics, it's simple physics. If you put 9lbs of hot dogs, and 9lbs of cotten on a scale they still equal 9lbs, which is done by a spring in the scale. Over complication of things, leads people to think you have to have a degree in fluid dynamics, lol.

 

While your analogy works for a standard wieght of an object forcing action on a tensioned load it does explain nor quanitfy the reaction of a fluid (air) to a change in temperature or other environmental factors. For example when exhaust gas cools it expands. If there is no where for it to go (backpressure) the pressure inside the cylinder will increase. While I am not making an assumption as to the cause of this or that a compressed intake charge will expand in cold weather I'm merely stating that you cannot explain away the laws of fluid dynamics with hot dogs and cotton *****. I'm interested in getting a Mechanical Engineers persepctive on this as most if nto all of them have some knowledge of fluid dynamics. Tony (Hydrazine) where you at? And if you honestly think that a fluid acts like a solid when compressed and altered by a environmental source then theres no point in discussing this with you any further.

 

What you're trying to understand is what I said in a more round about way. It's NOT a problem with air, it's a problem in the design of the TK Flow is going through the least place of resistance, which in a bad design isn't always where it should go.

Again, cold air doesn't cause problems, it's a bad design.

 

Thats funny, someone with an APS turbo kit posted a similar experience a while back. Is that a bad design as well? I'm not saying its a "problem" with air either. And since you obviously know more about turbocharger and turbo system design then me please enlighten me on how the design could be altered to correct this specific problem. Thats WITH the update piping of course. If you know its a bad design please point out the specific area of the design which needs to be addressed for this problem to be corrected. If you have a better design in mind please share the merits of the design change and what goal/performance targets it would achieve over the current design. Any research data you have would be helpful. Test cases, flow improvement diagrams, back pressure test results, etc.

 

For the record I do have a background in fluid dynamics, compressors, turbines, etc.

Boost is not equal to weight.

It's PSI, pounds per square inch. The "pounds" people usually think of are pounds of WEIGHT. But in terms of PSI you have pounds of FORCE acting on a given area...hence pounds per square inch.

nevertheless, if the spring actuator opens at 9 PSI, then there's no logical explanation why it should open at 10 PSI in cold weather.

I'm trying to work on an explanation:

You start with colder air. You compress it in the turbines. Since it's colder than usual, you have put a larger MASS of air through the turbines due to the fact that you started with colder air. With colder air, you will have more air molecules, even though the pressure is the same.

Now, the intercooler is going to be more efficient at lower ambient temperatures. That means you will have more cooling, at a given pressure. All this equates to having a higher MASS of air compared to normal, even if the pressure is the same, you will have more MASS (due to higher density).

The engine itself does not run significantly cooler in colder air. The reason for this is the thermostat.

So, you have a nice dense (and colder than usual) charge of air coming out of the intercooler. All of the sudden it hits your engine (same temperature as usual), intake manifold, whatever. It suddenly heats up, which increases pressure.

All of this is true.

(Now, the part I'm not sure about...) Perhaps the wastegate cannot keep up with relieving all the excess pressure from the SUDDEN expansion fast enough, and you read a slightly higher pressure than normal.

 

Actually your explanation makes perfect sense and to be honest I think you are just about there. In most (if not all) 350Z turbo systems the wastegate signal used for opening the wastegate is sourced from the compressor outlet. This is true of almost every turbo kit on the market. As such the wastegate is opening when it sees 9 PSI of compressor outlet pressure. It does not ever see or reference the pressure measured at the intake manifold after the intercooler, etc. However most if not all people tap the pressure source for their boost gauge at the intake plenum port. This would explain the variance. The wastegate continues to open as it always has when it sees 9 PSI of compressor outlet pressure while the colder air in charge piping increases pressure at the manifold giving a higher pressure reading on the gauge as that is where it is referencing the pressure. So the system is in fact working correctly. And just for reference ANY turbo system that is running on wastegate tension and compressor outlet pressure alone could do this given the right conditions. That means Greddy, PE, SFR, etc.

 

I don't see any increase in boost from 100 degrees ambient all the way down to 30 degrees ambient. Always sits right on 9psi.

 

I agree, unless someone invents a way for the wastegate to relieve pressure instantaneously...

you're right, the variance probably has something to do with where the pressure sensor is located.

 

Actually if the APS system, and it does have a huge problem without External waste gates, is a bad design and why they are trying to figure out a design that doesn't increase in boost.

Wired 24/7 said basically the same things as I did, and has a background you're looking for....fyi, I went to college and have a BS in Natural Resources and Engineering if that makes you feel like I know what I'm talking about, but the stuff I'm telling you is learned in HS physics.

The bad design is when something in the system changes beyond what they tested for.

The TN kit was designed around stock exhaust (no real idea why since you'd expect somebody upgrading to a TK to have upgraded the exhaust) But anyway, before the stock exhaust was the pressure spot, and when the boost need somewhere to go the WG was the past of least resistance. When changing the exhaust to near Zero back pressure that made it the least resistance and therefore made the WG the restriction and resulting in boost creep.

APS has something similar, and actually one guy has changed several things and cannot stop the boost spiking. It's not because of COLD air, but the design of the system

You can try to spin, or ask a rocket scientist to come here an explain it but the extra boost is NOT from cold air, it's from a system that has a fault. Could it be the pressure sensor is in a bad spot, sure but that still bad data and again poor design.


There are lots of car with examples that don't have this issue, and the air changes with them too

 

So you are telling me with a stock exhaust (since you clearly know more about the Turbonetics design and testing then me) this would not happen? I know that it does from personal experience. I don't care what degree you have or where you got it. Unless you have experience in this particular subject your explanation is just conjecture on your part. Again since you know so much more about turbo system design tell me exactly what change could be made to the Turbonetics to correct this issue. You have now claimed that both the APS and Turbonetics systems are flawed by default. Since you must be qualified to make those statements can you please back them up with what you would do to correct the design flaws that you clearly see in the design. From an engineering perspective would be great since you have a degree in it and are clearly more versed in turbo system design then engineers at both Turbonetics and APS.

 

Don't be angry at me because they have a design flaw. Try to make me look bad, but both TN and APS have had problems and redesigned their systems in ST to try and fix it.

So unless GOD changed the air, a system that has these issue has a problem in design, NOT A PROBLEM with cold air which I repeatedly said is NOT the cause of this problem. Even you said above it was a problem with the system and the magical "fluid dynamics." So instead of trying to insult my intelligence and everybody here that understands air temp isn't reponsible of the above problem, just soak it in and realize your TK, APS, and maybe others aren't perfect.

Never did I say your system sucked, just that the problem is not a change in air, but a system that is flawed and in certain conditions the problem is more pronounced than others.

I didn't post my degree to be smart, but if these companies want the opinion of a fluid dynamics engineer....hire one when you design it.

 

My point is that you have continuously pointed out in this thread how you believe the systems are flawed yet you clearly have neither the credentials or epxerience to be making those claims. Someone WITH a fluid dynamics background has already posted his take on the situation. I'm not saying I am right nor am I saying you are right. I'm saying that since I don't have the sufficient education in this subject to provide the answer I would like someone who does to weigh in on this discussion. Just because you think its a system design flaw doesn't mean it is. And if you are going stand by your claim that you KNOW the system design flaw is the reason this occurs in cold weather on this kit you should be able to back up your statements. I still have yet to see you post YOUR explanation of exactly what flaw you believe the system has the creates a variation of pressure ratios in the cold. SO honestly tell me, what part of the system is causing the boost pressure measured at the manifold to increas ONLY WHEN ITS COLD. That would be a very unique design flaw indeed and I think we all would like to know your thoughts as to the cause since you must have one to say that said flaw is the reason for this. The ONLY arugment/explanation I have seen in this thread that makes any form of sense regarding the CAUSE of this is the post made by Wired who surprise surprise DOES have a fluid dynamics background. But if you stand by your statement of the design of this turbo system being the flaw PLEASE tell me what flaw that is. What system design flaw causes the measured pressure at the manifold to increase ONLY in cold weather? I'm not trying to make you look stupid you are doing a good job of it on your own. You are telling me that a design flaw will cause a turbo system to produce dead on repeatable pressure ratios in warmer temperatures (never seen above 8.5 PSI in temps above ~40) but somehow causes that pressure ratio to increase ONLY when its cold although temperature is not referenced to boost control anywhere on either system?