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Old 07-01-2012, 12:27 PM   #1
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Default Sticky Request - Miata Airflow Spreadsheet

Please find below, the link to an Airflow spreadsheet I created for use with DIY Turbo Kits, or anyone seeking an upgraded turbo to meet their goals.

If anyone has any suggestions, such as a higher VE to use etc... Please feel free to let me know and I will update the spreadsheet as such.

Also, if anyone notices a problem with my math, please let me know as well.

https://docs.google.com/spreadsheet/...zZGOXQya3p6MGc

Last edited by TheGrim; 07-01-2012 at 12:46 PM.
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Old 07-03-2012, 08:25 PM   #2
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mass air flow seems high, optimistic.
what turbocharger are you basing this on?

Last edited by Techsalvager; 07-03-2012 at 08:37 PM.
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Old 07-03-2012, 08:58 PM   #3
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These numbers are not for a specific turbo. This simply shows the airflow numbers for a 1.8L engine operating at 80% VE. The numbers you see at different psi is where the motor itself will flow and are meant to be plugged into a compressor map to help with selecting a turbo for any application given "x" boost level.
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Old 07-03-2012, 09:06 PM   #4
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what I mean is I don't think you can say at 8 psi you will have this much air mass flow at this rpm.

at 8psi with one turbo you at say 7000 revs you may have 120 grams a seconds vs another turbo being at 160 grams a second
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Old 07-03-2012, 10:02 PM   #5
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Basic misunderstanding of how turbos work.

Need to go by mass of air moved, not on pressure or pressure ratios.
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Old 07-03-2012, 11:38 PM   #6
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Are you saying I am misunderstanding? Or tech doesn't understand?
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Old 07-04-2012, 12:38 AM   #7
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Quote:
Originally Posted by Techsalvager View Post
...mouth diarrhea...

at 8psi with one turbo ...more terrible grammar... 120 grams a seconds vs another turbo
Quote:
Originally Posted by Nagase View Post
Basic misunderstanding of how turbos work.

Need to go by mass of air moved, not on pressure or pressure ratios.
You guys are missing the point of what he has calculated. His spreadsheet calculates mass flow through the engine at a given pressure ratio so you can figure out which turbo to pick. With these calculations you can simply think about the engine as a pipe. Air goes in one end, and out the other. With no pressure, using some math, you can figure out how much air flows through that pipe at any given RPM. Now, the pipe doesn't change size. If you increase the pressure ratio (pressure on the inlet divided by atmospheric pressure) more air flows through the pipe. It doesn't matter what is creating that pressure ratio, supercharger, turbo, leaf blower, whatever. Now that you know how much air is flowing through your engine, you can look at compressor maps and see if the turbo flows comparable amounts of air at the given pressure ratios. Yes, turbos flow different amounts of air at the same pressure ratio based on what size they are.
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Old 07-04-2012, 01:00 AM   #8
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tell you what, instead of trying to guess someone with a bone stock 1.8 miata and megasquirt 2 or 3 can easily figure out what the 1.8 will flow in terms of grams a second.
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Old 07-04-2012, 01:04 AM   #9
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Tech stay off my threads. I have been to a few of yours, and it is clear you lack ANY understanding of how systems work. Also, your grammar sucks, I don't even understand your prior post. Nothing that I calculated is GUESSED (minus volumetric efficiency). It is all SCIENCE and MATH. Baron, thank you for being the first (or second) person to understand my thread and the point of the chart
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Old 07-04-2012, 01:25 AM   #10
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Quote:
Originally Posted by TheGrim View Post
Tech stay off my threads. I have been to a few of yours, and it is clear you lack ANY understanding of how systems work. Also, your grammar sucks, I don't even understand your prior post. Nothing that I calculated is GUESSED (minus volumetric efficiency). It is all SCIENCE and MATH. Baron, thank you for being the first (or second) person to understand my thread and the point of the chart
Few of my threads like which? Post them up I like to see which.
Then since I'm so ------- stupid and lack understanding. Explain to me how you are gonna use this data to match up turbos. Like I said before I"m always open to learn.
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Old 07-04-2012, 01:43 AM   #11
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Quite simple. You match the airflow on the second part of the spreadsheet (LBS/min) with appropriate boost level, and line it up (with pressure ratio) on the maps for the turbo to see if you are in the best efficiency range. There is a great full article here: http://www.mygen.com/users/dbruce/my...sor%20Maps.htm
This will even show you how to use the maps and plot your data. Both our charts are laid out the same way, so it should be easy enough to compare the two. It's really hard to go wrong with listing data in a chart

Last edited by TheGrim; 07-04-2012 at 01:57 AM.
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Old 07-04-2012, 10:42 AM   #12
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Quote:
Originally Posted by Techsalvager View Post
what I mean is I don't think you can say at 8 psi you will have this much air mass flow at this rpm.

at 8psi with one turbo you at say 7000 revs you may have 120 grams a seconds vs another turbo being at 160 grams a second
Stop being a retard. If you have 8psi in the intake manifold its very simple math to figure out how much air passes through the nozzle of the intake valves given a certain lift and duration. The killer becomes if you try to be accurate and consider the opening and closing times of the valve. This is turbo/sc/na/leafblower independent, the calculations don't care how 8psi is being generated in the intake manifold.
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Old 07-04-2012, 11:42 AM   #13
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Quote:
Originally Posted by thegrim View Post
nothing that i calculated is guessed (minus volumetric efficiency).
ílol!
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Old 07-04-2012, 01:20 PM   #14
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I came across something like this a long time ago and have had a copy saved for awhile... kinda fun to mess around with, gets you in ballpark I guess....but yes the VE is the big unknown.
Attached Files
File Type: xls Airflow.xls (18.5 KB, 113 views)
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Old 07-04-2012, 06:42 PM   #15
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I figured anything from 80%-85% wasn't going to provide numbers that were way off. I will check out the other spreadsheet when I get home tonight. What is a good VE to assume with the miata motor? I normally just use 80% to keep it safe and (somewhat) predictable.

Last edited by TheGrim; 07-04-2012 at 07:20 PM.
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Old 07-16-2012, 11:05 AM   #16
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Bump. Anyone have any info regarding the VE on a miata? I assumed 80%. Anyone agree/disagree with that number?
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Old 07-16-2012, 11:30 AM   #17
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Anyone with a megasquirt 2\3 on a non turbo stock engine could figure it out.
I would probably expect max VE to be near 88-90% near peak tq output
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Old 07-16-2012, 06:37 PM   #18
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Quote:
Originally Posted by Techsalvager View Post
Anyone with a megasquirt 2\3 on a non turbo stock engine could figure it out.
I would probably expect max VE to be near 88-90% near peak tq output
That number would only be accurate if you had accurate fuel injector data, no ones has that. The people who made the injectors might but it would be for a nominal injector to come off the line and not something on either end of the tolerances. And they would only have it for some pressures and delta-p's. You'll be within 5% though. Assuming that you dont have to fake anything else on the tune, like actually putting in the correct displacement, and setting the iat and ect modifiers to zero for the conditions the engine was tuned in.
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Old 07-17-2012, 09:20 PM   #19
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My intuition says the VE for our weak little BP motor is probably closer to 70% or lower. A quick google search shows VE is equal to the actual air flow through the motor divided by the ideal air flow. Given the generally terrible flow characteristics of the cylinder head and stock intake manifold, I would say 80% is probably on the high end.

Some more quick googling turned up a paper that calculated the VE of an F20 motor out of an S2000 to be about 100% average, spanning from 85% ish in low RPM to over 100% on the high end. Given the amount of power/displacement that motor makes vs the BP, my seat of the pants math/engineering intuition says the miata motor would be doing pretty darn well to be at 80% VE. But this is all speculation based on some quick searching and educated guesses. It would be nice to see some actual calculations based on a mass air flow datalog.
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Old 07-17-2012, 09:48 PM   #20
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If we had a calibration curve for the MAF, we could easily read the flow and calculate VE. Never heard of one though.
With a 1.84l engine (NB) each 360deg rotation should pump 0.92l of air. We can easily measure air temp, that, combined with mass air flow would give us volume air flow. We also measure rpm and therefore:

VE = VAF [l/min] / 0.92l * rpm

Or I could be wrong :-)
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