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Old 03-01-2004, 12:02 PM   #1
no-coast-punk
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Default nifty utility I have been working on...

Hey guys, I have been burning up time in class lately working on a nifty utility. You input ambient air pressure, displacement, # of injectors. And then fill out a small table with engine rpm's, volumetric efficiency, desired fuel air ratio, and manifold pressure (positive or negative) and it will give your pressure ratio, airflow in both lb/min and CFM (extremely useful for running compressor maps). Fuel delivery in lb/hr, Lph, and lb/min (perfect for picking the proper fuel pump). And it also gives you the injector size you need in both lb/hr and CC (both figures include a max 80% duty cycle). It also gives you the gallons per hour your car is consuming and given a certain vehicle speed also gives you your approximate fuel mileage.

*edit* I added the fields for heat correction and altitude.

The problem I am having is, I need somebody to host the file (it's a microsoft excel spreadsheet weighing it at ~22kbytes).

Let me know what kind of interest there is in this and if anyone can host it. I would also appreciate any feedback you guys could offer. I am currently working on making it more accurate and adding more correction fields (there are currently no corrections for air temp. humidity, etc.)

In it's current state it is suprisignly accurate when fed with all the parameters of my current setup (the mileage it says I should be getting is only .5mpg off real world).

PM me or e-mail if you can host the file.
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Last edited by no-coast-punk; 03-10-2004 at 08:48 PM.
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Old 03-01-2004, 03:30 PM   #2
amelnikov
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I can host it for you.

Alex...
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Old 03-02-2004, 10:57 AM   #3
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Ok everyone, the file is off to amelnikov *eagerly awaits it getting posted* Oh yeah, I also added a field to calculate APPROXIMATE horsepower late last night. Being that I have no real thermal efficiency numbers for our motors it isn't very accurate. But It should be within 10-15%. Oh yeah.... this also works for NA cars too, just enter the appropriate negative pressure numbers (in PSI) and it will tell you what you need. Any feedback/flames/refined numbers and calculations would be seriously appreciated. Post any suggestions or changes you have in here.
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Old 03-02-2004, 12:11 PM   #4
amelnikov
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Ok here is the link to the page.
Link

It's in the downloads section.
Or a direct link to download the file

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Old 03-02-2004, 01:56 PM   #5
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wow, thats pretty cool. I don't really know how it all works, but it looks like it could be very usefull.
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Old 03-02-2004, 02:20 PM   #6
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cool...

So if I'm near sea level altitude, I should set Ambient air pressure to 14 psi?

How would you figure out your car's volumetric efficiency since it varies upon load, correct?

What about ignition timing parameters?
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Old 03-02-2004, 02:52 PM   #7
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Loomis, how it works is fill in all the cells that are blue with the proper values. If you don't know a particular value, leave it alone. The closer you get the values to the real world the more accurate it will be. I origionally wrote this for making it much easier and faster to plot compressor maps. But when I had it all together I realized how easy it would be to add a few more cells to get some really interesting data.

cRayZee, air pressure at standard temp and humidity is 14.7 PSI. Humidity and air temp affect ambient pressure quite a bit which why I need to add in provisions to correct for it, however the calculations to do that are pretty long and involved which is why I'm asking for help on this because I don't have much free time these days. As for the volumetric efficiency...

http://www.protekperformance.com/rv7...dyno_graph.htm

There is where I got my data, it is for a stock EJ25, I don't know how accurate it is... but those aviation guys are pretty anal retentive when it comes to numbers, so it's probably reasonably accurate. Being that I am using stock EJ25 heads I figure they are reasonably accurate. There are ways to calculate your VE with a reasonable degree of accuracy, but as for now that is outside the scope of this project.

As for the ignition timing.... that effectively varies your thermal efficiency, when I get more time and if I can come with some better hard numbers I will change that field to be varied with RPM's.
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Old 03-02-2004, 02:52 PM   #8
amelnikov
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You can figure out your engine's VE with this little utility.

http://alexperformance.com/Downloads/EngineVE.zip

Alex...
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Old 03-02-2004, 02:56 PM   #9
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Alex... any chance that you could post the raw un-zipped files anywhere? I would like to take a look at that VE utility but I don't have privelages to install winzip on this machine and I have no 'net access at home right now.
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Old 03-02-2004, 02:57 PM   #10
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Give me 2 minutes

Alex...
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Old 03-02-2004, 03:02 PM   #11
amelnikov
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Here you go.

http://alexperformance.com/Downloads/EngineVE.exe

Alex...
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Last edited by amelnikov; 03-03-2004 at 04:09 PM.
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Old 03-02-2004, 04:06 PM   #12
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How do we get volumetric efficiency and manifold pressure?
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Old 03-03-2004, 08:58 AM   #13
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VE is tricky, either use the utility alex posted or use the default values for the stock EJ25 that are already in there. The problem with the utility alex posted is that you have to use VE numbers your motor would put out with no turbo.

Manifold pressure is what your boost guage is reading or what your map sensor readout is with a scan tool.
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Old 03-08-2004, 10:59 AM   #14
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Ok guys, I have sent the newest version of what I have been working on off to Alex, hopefully he'll post it later today. I added corrections for ambient temperature, altitude, intercooler efficiency, and compressor efficiency. On the whole it is MUCH more accurate and MUCH more informative. I was pretty suprised to see a few things, such as how you need larger injectors at altitude and how completely overkill alot of the fuel systems people are running. I dunno, as usual let me know if you guys have any thoughts.
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Old 03-08-2004, 11:21 AM   #15
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The file has been updated. Use the link on top to get to it.
No-coas, this is some impressive work.

Alex...
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Old 03-08-2004, 02:29 PM   #16
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Thanks.

The only thing I really have left to do is to add values for relative humidity and it's going to be as accurate as I can get it without better numbers for thermal efficiency and VE or without a way to get the freaky lograthmic curves into for altitude vs. air density and pressure ratio vs. heat correction factor. As is it's pretty darn close, the numbers in it are probably within 5% of real world. I can probably get to within 2-3% once I add values for humidity. Beyond that it's all up to better VE and TE numbers.

Past that I can't really think of anything else to add, I'm open to suggestions.

I am considering adding all the numbers to calculate torque.... but that gets REALLY complicated (have to calculate cylinder pressures all the way down the bore and what not), but I'm still not ruling it out.

Another thing I am considering adding is fields for piston velocities at varying speeds so you can see what kinda rod ratios would be good for your target engine speed. Also to satisfy my curiousity as to just what exactly our piston speeds really are. Who knows if I had enough time I could probably have the thing calculate thermal efficiency by giving it the surface area of all the metal -> metal contact points in the motor... wouldn't that be cool.


Oh yeah, if there are any people out there good with VB, get in touch with me, I'd like to get a better/easier to understand front end.
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Old 03-11-2004, 04:57 PM   #17
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One other thing, I think I figured out what I want to add next but it has been a REALLY long time since I was in my engineering classes. Does anybody have any suggestions on how to calculate port velocity?
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Old 03-11-2004, 05:17 PM   #18
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Wow, it's been a while for me too, but from what I remember it's pretty complex, you need shape, size and pressure differential as well as air density.

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Old 03-12-2004, 11:00 AM   #19
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I know you needed the size as well as your pressure differential and air density, and I don't remember shape factoring into it very much because that was covered under your pressure differential (a well designed venturi for example will have a larger pressure differential than a straight tube).
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Old 03-12-2004, 11:25 AM   #20
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Shape has a lot to do with velocity. Just ask any head porter.
It's also one of they "gray" areas that everyone will give you a different answer about.
However I think you can get pretty close with just area and pressure differential.

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Old 03-12-2004, 12:30 PM   #21
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Couple questions:

I didn't see any corrections happen when I adjusted the altitude box - where does it show up in the calculations?

I was adjusting the ambient pressure up, and horsepower dropped - this is counter intuitive. The boost stayed at the same value so I thought I should get more horsepower, not less at higher ambient pressure (lower altitude). The pressure ratio and Density ratio drop(as they should), but overall there should be more air going in, which should show up in lb/min airflow.

Overall a great spread sheet, I've done some of the same stuff, although not to the level of detail you have here.

Tom

Last edited by SlideWRX; 03-12-2004 at 12:37 PM.
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Old 03-12-2004, 02:53 PM   #22
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ambient air pressure is modified by altitude (and soon air temp).

You are right about the air pressure doing screwy things . I see where I screwed up, it's where lb/min of airflow gets calculated and most everything else is based off that. It worked fine before I added altitude correction and used a static value for air pressure but it gets really wierd now, I'll fix it this weekend if I get time, but seeing as I just got a J&S and a sweet x-box mod chip in the mail I might procrastinate on this for awhile.
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Old 03-16-2004, 05:04 PM   #23
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Ok, a new version is off to alex. I cleaned up a few things, added a field for charge air temp in farenheight. Soon I'll a few more fields for metric stuff in case the compressor map you have is in metric.

As for the altitude thing, upon further review I don't think I did screw up, and I cleaned up a few things. Why the altitude is accurate is because generating the same ammount of boost between sea level and high altitude is much harder. You have to flow alot more air to generate equivalent boost levels and your pressure ratio increases alot.

I still have to add a few things like more metric/standard conversions and what not and clean up some of the math (Instead of calculating raw numbers for a few things I use previously calculated values leading to some rounding errors and what not). After that I'm going to try and play around with torque and port velocity.
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Old 03-16-2004, 07:43 PM   #24
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Ok file has been updated.

Nice job.

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Old 03-16-2004, 08:33 PM   #25
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thanks
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