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  #1  
Old 06-14-2007, 11:58 AM
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Click here to download a HOT supermodel with BIG BOO...

...ST capability for evaluating turbo upgrades and many other mods to see how well your truck STACKS UP against mine. I've got an early 99 with limited mods, and it huffs & puffs to make 260 RWHP on its best dyno run, so I'd rate it between an A-CUP=Stock, and a B-CUP=275 RWHP. I know they're plenty of C-CUPs out there in the 300+ RWHP range, but I'm not sure how much RWHP it takes to be considered a true D-CUP because I've never been in a strip club to see what one actually looks like! Yes, I had to consult with the wife to come up with this highly precise unit of measure for engine performance.

The screen in the pic below is filled in with my user input data (green), and these inputs give outputs (MAF, VAF, RWHP, GPH, and MPG) that match the performance of my truck pretty well. As shown in the pic below, the model predicts a 260 RWHP that peaks at 2800 RPM and 20 psi boost for my truck. If you want to see how your truck stacks up, I suggest downloading the Excel file and using the "save as" feature to create your own versions, then adjust the user inputs until you see a RWHP curve that matches your truck's performance under the assumed input conditions. Then you can run that model for different throttle settings, different gears, ambient air temps, etc... and see what effect those changes have on your performance.

If you've got a 99.5 or later truck with a chip, start by increasing the VENR input from my 78% to 83%. This adjustment increases your air flow to account for your larger inlet boots and plenums compared to those on my early 99, a footnote discusses this effect. This change alone puts you in the lower range for a C-CUP, and then you can fine tune from there, by increasing the VERSF,VEBSF,TERSF,and TEBSF parameters in increments of 0.1% at a time, until you match your RWHP curve. These parameters control the volumetric (air flow) and thermal (BTU to HP conversion) efficiencies as a function of RPM and BP, and control the shape and magnitude of the RWHP curve. If you know your turbo compressor efficiency at your maximum HP operating point input that number in place of my estimate, likewise for your intercooler pressure drop and heat exchanger efficiency.

Here's the link to the supermodel.......The only way I can get the link to work, is to first open my Internet Explorer and copy and paste the link there, and it works fine, as I did a trial download that way. Maybe after I post this the link will work on FTE, or I'm sure that Alan will be along to fix it at some point if there's a problem. It's a good thing it didn't work, because I forgot to thank Alan for all of his hard work on this project, test driving the model, putting up with the multiple revisions, and for hosting the link. Thanks Alan! I plan on stopping by Deatsville in April for paybacks!

http://www.7point3.com/PSDEM.xls

The first Tab provides a brief description of each user input, and several footnotes provide additional details. The AFR input is explained in a footnote, but since most are like me and don't bother with reading the instructions, the AFR value that you enter acts like the throttle. A value of 14.7 is WOT, and provides the exact amount of fuel to combust all the incoming air supply, and this produces the maximum possible RWHP. Use this setting to match against your dyno runs by adjusting other parameters which effect air flow and fine tune the model for your particular set up. Except for BTU content and density, they're aren't any adjustments for fueling except the AFR, and at 14.7 (WOT) this model assumes your chip can add as much fuel as is required to combust all of the available air supply. All the tweaks are for adjusting the air supply and thermodynamic efficiency as a function of RPM and BP, the fuel is controlled by the AFR input. For example, if you've got an upgraded turbo that has less back pressure for a given boost, this increases the thermodynamic efficiency, the compressor efficiency is a separate parameter to input as it effects the density of the air supply. Eventually I plan to model more details of the combustion process, and then details of your chip like injection timing, and dwell will be taken into account.

If you enter AFR values larger than 14.7, it's like operating at partial throttle, and you now get less than the maximum fuel delivery possible for the given supply of incoming air. The RWHP decreases accordingly, and there's left over air that doesn't get combusted. If you enter values less than 14.7, it's like pushing the throttle through the floor board, except this model will add more fuel than the incoming air supply can combust and the RWHP will increase as if some additional air had magically materialized to burn the extra fuel, but this result has no physical significance. I was going to include a hard limit at 14.7, but I thought this would lead to confusion when users inputted smaller values and saw no change in RWHP. The bottom line is that if you change one of the many input parameters that influence air mass delivery, and leave AFR unchanged, you automatically get the appropriate increase or decrease adjustment in fuel delivery to combine with the new air supply to keep the AFR at the value specified in the input section.

Also, keep in mind that this is a spreadsheet based model. I replicated the formulas over all possible values of BP and RPM because this was easier and I wanted to see what came up in each cell to see trends etc... You need to apply some common sense when you use the model, as it's not yet complete. I haven't yet modeled the exhaust flow that spins up the turbine to turn the compressor to produce the boost. After I do, it won't show combinations like BP=30 psi at 600 RPM idle or 3400 RPM at BP=0 psi.

The two tabs for GPH & MPG require a little work to be meaningful. At first glance it looks like you're getting better MPG at 103 mph than at 65 mph, but only a few points on these two tables are physically possible for each value of AFR!

For example, enter AFR=26 in the Truck RWHP, Truck GPH, and Truck MPG tabs. The RWHP shows that at 65 MPH (2000 RPM) and BP=0 psi, you generate only 79 RWHP and looking above in that column you see that's only enough to cruise on the flat or up a very slight grade. Likewise, at 45 MPH you make 45 RWHP, or enough to climb a 2% grade. You need to color code these points (and others that match to various driving conditions) and copy and "paste special", "formats only" over to the other tabs and those color overlays show the cells that have meaning. Doing that you see 14 MPG at 65 MPH on the flat, and 15 MPG at 45 MPH going up a 2% grade. The 17 MPG at 103 MPH has no meaning! You need 255 HP to go 103 MPH, and then you only get 5 MPG doing it.

An AFR=35 matches my empty cruise exactly, at 65 MPH (2000 RPM) it takes BP=4 psi to get the required 69 RWHP, and for that combination of RPM & BP with AFR set to 35, the other tabs show GPH=4.3, and MPG=15.1. I included a pic of the AFR=35 example below. At 58 MPH, you get 17.9 MPG, and this drops to 15.1 MPG at 65 MPH. I've posted my drag model before explaining how the required RWHP increases as the (MPH)^3!

Well that should be enough for now to allow anyone interested to download it, play around with it, and see if they can get results that look correct for their truck. Let me know how you do, and I'll try to answer any questions.
 
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  #2  
Old 06-14-2007, 12:01 PM
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im thinking u have alot of time on your hands
 
  #3  
Old 06-14-2007, 12:03 PM
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You got me, I was actually hoping for the real thing lol.
 
  #4  
Old 06-14-2007, 12:06 PM
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Ernest... how long have you been working up this set of models?
 
  #5  
Old 06-14-2007, 12:09 PM
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After getting all hyped up on the BOO... thing it is kinda hard (no pun intended) to do all that reading. We'll get around to it.
 
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Old 06-14-2007, 12:09 PM
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lol nice, i fell for it
 
  #7  
Old 06-14-2007, 12:22 PM
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I haven't looked over the spreadsheet yet but I have a few questions I have about they way you set it up. The first think I notice is that you say AFR above 14.7 is like part throttle. By my references the stoichiometric AFR for diesel is 14.3. This will not make a big difference but some. Also are you assuming the the engine is running stoichiometric or a little bit rich. The reason I ask is that from the engines classes I have taken we were always told that diesels run lean. equivalence ratio is usually between .3 and .8 if I remember correctly.

Just my thoughts

--Darin
 
  #8  
Old 06-14-2007, 02:54 PM
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I think anyone this ate up with deserves more than one truck, let's take up a collection. Funds collected through PayPal name [email protected]
 

Last edited by 7.3L DID TD; 06-14-2007 at 03:00 PM.
  #9  
Old 06-14-2007, 03:15 PM
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Originally Posted by jvoigt
You got me, I was actually hoping for the real thing lol.
Originally Posted by country2
After getting all hyped up on the BOO... thing it is kinda hard (no pun intended) to do all that reading. We'll get around to it.
Originally Posted by lukecline
lol nice, i fell for it
The download link works ok, I think my internet security software was blocking access! BTW, are all of the above disappointed repliers sure that the model doesn't contain some visual references for estimating CUP SIZE, which I'm using as the new improved unit for measuring engine performance?
 
  #10  
Old 06-14-2007, 03:25 PM
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Still no supermodel! Me dissapointed lol j/k
 
  #11  
Old 06-14-2007, 03:26 PM
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I got the joke b4 i opened it but i was still hoping lol.
 
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Old 06-14-2007, 03:51 PM
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??

Are you serious about never going to a strip club???
 
  #13  
Old 06-14-2007, 05:43 PM
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So now i know you do at least two things in your free time...
 
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Old 06-14-2007, 05:53 PM
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Originally Posted by strokin_it7.3
So now i know you do at least two things in your free time...
 
  #15  
Old 06-14-2007, 06:01 PM
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Originally Posted by dc2842002
I haven't looked over the spreadsheet yet but I have a few questions I have about they way you set it up. The first think I notice is that you say AFR above 14.7 is like part throttle. By my references the stoichiometric AFR for diesel is 14.3. This will not make a big difference but some. Also are you assuming the the engine is running stoichiometric or a little bit rich. The reason I ask is that from the engines classes I have taken we were always told that diesels run lean. equivalence ratio is usually between .3 and .8 if I remember correctly. Just my thoughts--Darin
I notice you have a 6 speed manual, why don't you post those gear ratios because I only had the ones for my auto. Just plug the manual ratio for your gear of choice into the TR cell like I did for my auto.

I've covered the topic of AFR for a diesel in some detail in a footnote. As you can see on this link... http://www.eng-tips.com/viewthread.cfm?qid=130502&page=1 the subject usually leads to a lively debate. If you read this thread you'll see that, as is the case in most debates, many of the participants espouse opinions that are incorrect. If you read to the end of the thread, the expert chemist steps in and straightens everyone out!

The quote below is from the chemist, and I was going to use his AFR=15 result, since it's a nice round #, until I found one that said 14.6 was a better estimate for #2 diesel, so I just decided to use 14.7 since everyone is familiar with what that number means, namely optimum AFR in "some sense". When you delve into the model you'll see that as I mentioned in the lead in, I haven't yet modeled the actual combustion process, but I do show an outline for doing so.

EDIT: The following isn't correct, the exact AFR value is required to get the exact RWHP! See my follow up post.

For now I only use the 14.7 value to scale the HP vs AFR for higher ratios. For example, AFR=29.4 halves the fuel and HP output. If I'd used the 15 result, then it would be 30 to halve the fuel, etc... so for now the precise value (which varies with the O2 content of the fuel) isn't important. For now, the heat from combustion is captured in the BTU content and fuel density parameters, and included in an overall net thermodynamic efficiency parameter for converting BTU/hr to HP, that scales as a function of RPM and BP.

"The original question mentions 14.7 so it's pretty sure the intention was to find out the stoichiometric air fuel ratio.

CxHy + a(O2+0.79/0.21N2) => xCO2 + y/2H2O + a*0.79/0.21N2
where a=x+y/4 since a C can use up a whole O2 and an H can only use 1/4 of an O2. The 0.79 and 0.21 are the proportions of N2 and O2 in air.

If you take the formula for a hydrocarbon reacting with air you can easily work out how much of each is required.

molecular weight of O2 is 32 and N2 is 28.
Octane C8H18 has a=12.5 and molecular weight 114 ( 8 12's are 96 plus another 18).
Dodecane C12H26 has a=18.5 and molecular weight 170.

So if you crunch the numbers to get the AFR
AFR = a(MWO2+0.79/0.21*MWN2)/MWfuel
you get 15.06 for petrol and 14.95 diesel.

Since hydrocarbons are mainly H-C-H, two to one, and the odd hydrogens at the ends making the difference are light, all the hydrocarbons will have similar stoichiometric air fuel ratios, with the exception of the very light ones where the two extra hydrogen makes up a significant proportion of the weight. Take CH4, the H-C-H weighs 14 and the two H's weigh 2. That's a large portion compared to 2 in 114 or 2 in 170.

So AFR for methane calculates to 17.2 and Ethane to 16.1.
Then propane 15.6 and Butane 15.4. You can see the figures closing in on the figure 15 for petrol and diesel.

Now if you add oxygen things change drastically since oxygen in the fuel means you need less oxygen from the air. And since air is 4/5 nitrogen, if you can cut down on a certain amount of oxygen then you reduce the amount of air you need by a factor of about 5, (drop 4 N2s for each O2 dropped). So the AFR for a fuel like ethanol works out to be about 9.

Now if you say that US gasoline is like petrol but cut with about 5% ethanol you can calculate 5%*9 + 95%*15 = 0.45 + 14.25 = 14.7 and get anAFR for gasoline.

So providing the diesel is all hydrocarbon based the AFR will be around 15. Diesel of plant origin (biodiesel) has oxygen in it and the AFR will be lower and mixtures would be in between, in the same way that the AFR for gasoline is between that for petrol and ethanol, heavily weighted towards the petrol figure. I don't think the figures change much if you take air as being 78% Nitrogen and 1% Argon instead of 79% Nitrogen and as I said before, changing one heavy hydrocarbon for another won't make much difference, ie calculating diesel as a coctail of hydrocarbons would only complicate the calculations and not significantly change the result."
 

Last edited by ernesteugene; 06-14-2007 at 06:50 PM.

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