Originally Posted by Braineack
(Post 1214933)
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. 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? |
Originally Posted by Braineack
(Post 1214933)
...
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.
Originally Posted by Braineack
(Post 1214933)
...but I don't you're going about determining that correctly.
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Leafy, does my math look ok, or is there a units error or something else off?
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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. |
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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Pat I think you're math is good. But I really really fucking 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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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. https://www.miataturbo.net/attachmen...1&d=1426433585 https://www.miataturbo.net/attachmen...1&d=1426433585 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. https://www.miataturbo.net/attachmen...1&d=1426433585 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 40°F day, and still 180°F 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 63°F intake temps from a WAI after IC vs. 49°F on the CAI--that's still 1.385DR vs. 1.348DR--so it doesn't really appear so. |
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. |
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. |
Originally Posted by patsmx5
(Post 1215140)
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.
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 30°C intake temps. |
Originally Posted by Braineack
(Post 1215146)
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 30°C intake temps. 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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yes. that's the math formula on their plots.
take the compressor map i was using: https://www.miataturbo.net/attachmen...ine=1426453553 inlet temp = t1c = 545° 545-460=85°F/30°C 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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What did you fix?
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Increase intercooler efficiency with increased Delta T
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Is intercooler efficiency usually in the 90's%?
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Originally Posted by Hinano
(Post 1215206)
Is intercooler efficiency usually in the 90's%?
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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.
Increase intercooler efficiency with increased Delta T 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. |
Originally Posted by Braineack
(Post 1215217)
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. ....Fuck 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 |
Originally Posted by nitrodann
(Post 1215222)
....Fuck dude.
Heat transfer coefficient - Wikipedia, the free encyclopedia Heat Transfer, Stefan Boltzmann Law, Heat Transfer Coefficient | Physics@TutorVista.com 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 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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