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Old 03-14-2015, 07:23 PM   #41
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Quote:
Originally Posted by Braineack View Post
you're ignoring a lot more than i am. and yes, you really lost track of your units, conversions, and relevance there.

here, this one factors in most:

Not2Fast: Turbo Calculator

it agrees that the change from 26.6*C to 82*C intake temps doesn't change the HP significantly once you input the rest.
I said I was ignoring everything, and did an example to show flow and pressure drop on the inlet side of a compressor.

What where did I loose track of units, conversions or relevance? I didn't check my math, but since you say it's wrong, what is wrong?
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Old 03-14-2015, 07:29 PM   #42
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Quote:
Originally Posted by Braineack View Post
...
you're forgetting how much a good IC equalizes the density ratio of the air that the motor ingests on each gulp. Yes, the turbo will have to work a little bit harder to compress that air, but I don't you're going about determining that correctly.
A lot harder, it now has to flow 27% MORE in my example to produce the same mass flow of air.

Quote:
Originally Posted by Braineack View Post
...but I don't you're going about determining that correctly.
If I'm wrong, and I may very well be wrong, please explain/demonstrate. I am not perfect! All I did was lookup the density online and work some maths with a calculator. Do you think I did it wrong, or do you know I did it wrong? If you know, what did I miss?
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Old 03-14-2015, 07:36 PM   #43
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Leafy, does my math look ok, or is there a units error or something else off?
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Old 03-14-2015, 07:41 PM   #44
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Maybe tomorrow am I'll reread everything and think about it more. but I really don't think you're looking at it correctly.

its time to cook dinner and get drunk on margaritas.
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Old 03-14-2015, 09:30 PM   #45
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Sounds like fun, I'm dissecting the factory wiring harness as needed, which surprisingly isn't going as bad as I thought it would. Keep having to look up connectors/wire colors which is always fun.
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Old 03-14-2015, 10:45 PM   #46
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Pat I think you're math is good. But I really really ******* hate doing fluids or thermodynamics work in imperial units. My step 1 when doing it with them on paper is to convert to metric because I've been burned by a weird unit conversion before. Its why I like mathcad so much, you can give your inputs units and it'll handle all the units conversion for you and tell you if theres a units mismatch.
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Old 03-15-2015, 12:35 PM   #47
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The losses at the engine are fairly low in my scenario--you're ignoring the DR completely and focusing at airspeed at the intake.

remove the intake altogether.

I'm suggesting on same day, with just different intake temps you might only lose 3% power from doubling the intake temps. You're still taking all that less dense air, then packing it back together after the intercooler, just not QUITE as well [3% less effective] because it's slightly warmer and more energized.





Losses of turbo efficiency might skew the numbers slightly, but that's going to be seen as slower boost threshold. Like how you can overboost on a cold day and underboost on a warm one, if using a MBC. Sure, you'll make more power on that colder day because the temps are lower and you're packing more air per volume. But the DR represents how effective your PR is. In a perfect world PR = DR.

To make up for the loses when it's hot, you spin the turbo a little more. The airflow on the turbo compressor map doesn't change but the speed/PR at the compressor outlet will increase to make up for it. Basically it just takes a little longer to make the boost pressure.



I may be oversimplifying it, but I think you're over-complicating it.

the intake temps may have doubled, but the IC being so effective brings the gains of 38% more oxygen to burn per volume down to 34%.

If it was a 40F day, and still 180F intake temps, then yeah the loss will be more significant for sure, would be nice to know what intake temps on an n/a miata typically reach using a WAI. But even here that's 63F intake temps from a WAI after IC vs. 49F on the CAI--that's still 1.385DR vs. 1.348DR--so it doesn't really appear so.
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Is cold air intake necessary on a turboed car?-180_degree.jpg   Is cold air intake necessary on a turboed car?-90_degree.jpg   Is cold air intake necessary on a turboed car?-boost_time.jpg  

Last edited by Braineack; 03-15-2015 at 02:33 PM.
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Old 03-15-2015, 03:36 PM   #48
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You are only looking at temps and PR's after the compressor, I was only looking at temps and PR's before the compressor. We're both "right" on those numbers. Your numbers show that the intercooler works to fix the density ratio, my numbers show that a restriction upstream of the turbo is very bad.

The point I was trying to make was that only looking at one number (temp, pressure, doesn't matter) doesn't give you the whole picture.

So making a statement that inlet temps are trivial, intercooler is key is wrong. There is more to it than that. We both know boost is a measure of restriction, that is important here! Your statement about "Losses of turbo efficiency might skew the numbers slightly" should be "will skew the numbers". It will. Anyone wanting to test this, go put a restrictor on the inlet of your turbo, or in the intercooler pipe, or in the downpipe, and report back. Air flows through the entire system, changing anything in the system will affect HP.

We're actually both oversimplifying it to be honest. We have not touched on what's happening at the turbine.

The whole point of my post was to show
1. As a system, changing one thing does change several things.
2. Some of the things that change are more important regarding HP than others.

I believe my post explains these two points, and that's all it was supposed to do. As I said, I don't have the software to model EVERYTHING that would be required to accurately calculate how much it would change hp.

But I do in fact have real world experience on this exact topic, and have done same day testing on this (hot air intake vs cold air intake) on a high boost turbo miata and confirmed that the SYSTEM flows more air through the engine with a cold air intake at THE SAME BOOST PRESSURE. So much so that I had to retune my fuel as the engine went lean with a CAI.
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Old 03-15-2015, 03:50 PM   #49
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And to add to my last post, the REASON the car had to be retuned/flowed more air is because the compressor on the turbo was more efficient (required less HP) to supply the boost pressure commanded with the CAI. So since it needs less HP to drive the compressor, the turbine doesn't need to supply as much power to it, so the wastegate can open up a bit more (let more exhaust go around the turbine to reduce power to the turbine). This drops turbine inlet pressure, which reduces the backpressure on motor and flow goes up. Thus more air, more HP, thus why I had to retune fuel when I installed my CAI on my turbo setup.

I was only running around 17 PSI back then too, so it would have been an even bigger difference on a high boost setup.
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Old 03-15-2015, 04:01 PM   #50
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Quote:
Originally Posted by patsmx5 View Post
You are only looking at temps and PR's after the compressor, I was only looking at temps and PR's before the compressor. We're both "right" on those numbers. Your numbers show that the intercooler works to fix the density ratio, my numbers show that a restriction upstream of the turbo is very bad.
I didn't ignore it, and a CAI would be more of a restriction... :P

lets take the intake tube completely out of the picture and only focus on the inlet temps.

its too bad Garrett and others don't provide turbo compressor efficiency maps at different intake temp values to actually see the effect on compressor efficiency; Garrett maps are done at 30C intake temps.

Last edited by Braineack; 03-15-2015 at 04:21 PM.
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Old 03-15-2015, 05:09 PM   #51
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Quote:
Originally Posted by Braineack View Post
I didn't ignore it, and a CAI would be more of a restriction... :P

lets take the intake tube completely out of the picture and only focus on the inlet temps.

its too bad Garrett and others don't provide turbo compressor efficiency maps at different intake temp values to actually see the effect on compressor efficiency; Garrett maps are done at 30C intake temps.
Garret publish their test data at the temperatures they are designed to operate at? No OEM designs their turbo car to pull in hot air, they ALL have a CAI. Feeding it hot air is going to reduce its performance and lifespan.

You can take anything you like out of the picture. I'm looking at the engine as a system. As a SYSTEM, a CAI on a turbo car is important for the reasons I have stated.
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Old 03-15-2015, 06:05 PM   #52
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yes. that's the math formula on their plots.

take the compressor map i was using:



inlet temp = t1c = 545 545-460=85F/30C
ambient pressure = p1c = 28.4 in.Hg. ~14psi
discharge pressure = p2c as seen in the pressure ratio equation on the x axis.

I already stated the MSM does not have a CAI (i dont think my 626 turbo did either), it sources air from inside the engine bay behind the headlight. granted there's a little hole to allow fresh air in, but it's not a cold air intake.

I don't disagree that having the lowest possible intake temps before and after turbo is a good thing, but I really think you're overstating how drastically important/beneficial it is. When you have a good working IC on your setup it eliminates most power losses between the extremes. Obviously you want to run the coldest air possible, but I don't think it's a make or break decision.
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Old 03-15-2015, 07:18 PM   #53
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Fixed





Dann
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Is cold air intake necessary on a turboed car?-180_degree.jpg   Is cold air intake necessary on a turboed car?-90_degree.jpg   Is cold air intake necessary on a turboed car?-90_degree.jpg   Is cold air intake necessary on a turboed car?-180_degree.jpg  
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Old 03-15-2015, 09:03 PM   #54
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What did you fix?
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Old 03-15-2015, 09:18 PM   #55
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Increase intercooler efficiency with increased Delta T
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Old 03-15-2015, 09:28 PM   #56
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Is intercooler efficiency usually in the 90's%?
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Old 03-15-2015, 09:57 PM   #57
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Quote:
Originally Posted by Hinano View Post
Is intercooler efficiency usually in the 90's%?
Depends on a lot of different things.
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Old 03-15-2015, 10:10 PM   #58
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yeah. that's probably a really good ic. just the number i picked, a good IC is probably somewhere between 80-90%. I wouldn't ever see very much over ambient boosting around over the years.

Quote:
Increase intercooler efficiency with increased Delta T
why would it do that?

IC Efficiency = ( compressor outlet - ambient ) / ( compressor outlet - air after IC )

I can see the efficiency dropping, or reaching diminishing returns, but not efficiency increasing as you add more heat to it. It can either exact the heat or it cant.
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Old 03-15-2015, 10:25 PM   #59
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Quote:
Originally Posted by Braineack View Post
why would it do that?

IC Efficiency = ( compressor outlet - ambient ) / ( compressor outlet - air after IC )

I can see the efficiency dropping, or reaching diminishing returns, but not efficiency increasing as you add more heat to it. It can either exact the heat or it cant.

....**** dude.

Heat transfer coefficient - Wikipedia, the free encyclopedia

http://physics.tutorvista.com/heat/heat-transfer.html

Rates of Heat Transfer

First 3 links on google, and literally high school physics.


TLDR-
Heat transfer rate depends on the materials, the surface area of the materials, and the difference in temperature between the materials.



Between this and the torque thread, I seriously think you and Vlad need to stop acting so authoratative.

Dann
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Old 03-15-2015, 10:34 PM   #60
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Quote:
Originally Posted by nitrodann View Post
....**** dude.

Heat transfer coefficient - Wikipedia, the free encyclopedia

Heat Transfer, Stefan Boltzmann Law, Heat Transfer Coefficient | [email protected]

Rates of Heat Transfer

First 3 links on google, and literally high school physics.

Between this and the torque thread, I seriously think you and Vlad need to stop acting so authoratative.

Dann
I'm not throwing insults at anyone, that doesn't help. I'm here to learn and help others. But I do agree that if you don't understand something fairly well, you shouldn't make statements as though you do. Because as you say, people read it and see who said it and just assume it's true. I know there's some other engineers on this forum, I wish a few of them would chime in and offer there experience/understanding on this.

You are correct about the heat transfer improving with higher delta T improving the effectiveness, but in your "corrected" pics you kept constant turbo efficiency which is a pretty large error, and what I kept trying to explain above. Do you understand why assuming it's constant is wrong?
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