RomRaider

I've seen a couple similar spreadsheets in here, but they all seem to make some nasty assumptions and are just difficult to use/read in general.

Hopefully this alleviates some of the problems with the others. No assumptions are being made here, everything is input. Atmospheric pressure, BSFC, VE, pressure losses before and after the turbo, efficiencies, RPM at peak power, etc. The outputs are air flow rate in lb/min, CFM, and g/s, the pressure ratio for the turbo, absolute and relative manifold pressure, air temp before and after the intercooler, total fuel flow rate, and injector size.

This sheet can be used for fuel system sizing, turbo selection, target boost selection, or just to see the change that an intake with less restriction would have on the required manifold pressure to hit the same power level.

A similar spreadsheet was posted on NASIOC a while back, but unfortunately there were a couple of bugs in the calculations that made it essentially useless. Not only that, everything was locked down so you couldn't even fix the bugs yourself, and the developer seemed to abandon the project almost instantly after posting it. This sheet is laid out like his, but it has some minor changes here and there. I came up with all of the equations myself though, since his was so locked down you couldn't even see the equations he was using.

Let me know if you have any questions, comments, or suggestions.

Im getting a circular reference error upon open the spreadsheet.

Yes, the MAP required for a given air flow rate depends on the post-intercooler temperature, the post-intercooler temp depends on the pre-intercooler temp, and the pre-intercooler temp depends on the MAP (pressure ratio to be more precise).

You need to tell Excel to do an iterative calculation. On my version of Excel you go to Tools > Options > Calculation, and check the check box next to "Iteration". 100 iterations should be plenty.

I should probably put those instructions in the spreadsheet itself, thanks for reminding me.

version 1.1 is up
I added a quick note about the iterative calculation setting at the top

I also added a second tab that lets you estimate your VE or BSFC based on data from logs. It doesn't read the log directly, it simply asks you for the temp/press conditions under which you did the test, your MAF g/s at peak power, RPM at peak power, and your peak power (which could come from Airboy's spreadsheet or a dyno chart).

Note: if you're running blow through, so you have a measurement of the actual post-intercooler temps, in the second tab when estimating VE, just set your ambient temperature to your post-intercooler temp and set your intercooler efficiency to 100%, that way you don't have to bother with incorrect compressor or intercooler efficiency or pressure drop estimates throwing off your VE calculation.

Keep in mind that while you could estimate your VE and BSFC for your car in its current condition, increasing the target HP (increasing the manifold pressure) will lower the VE and raise the BSFC from what you calculated. So if you start cranking up the target HP in the first tab, you should drop your VE and raise your BSFC a little bit as well.

version 2.0 is up

I decided that the way it was set up originally probably wouldn't be as helpful for people. So I moved the previous calculation to the second tab and called it "Reverse Calc". The first tab is now called "Forward Calc", and is probably a bit more logical.

It uses the same equations, rearranged slightly. Rather than giving the target HP and having it give you back the boost pressure, instead you give it the boost pressure and it gives you back the flywheel and wheel horsepower.

Now it's a bit easier to see the results of changes you would make to your car. Keep the target boost the same, and lower the pre-turbo pressure drop from say 2 psi to 1 psi (less restrictive intake) to see what effect it has on your post-intercooler temperature and horsepower. Change from the 93 octane lambda and BSFC to the e85 lambda and BSFC to see the horsepower and fueling change given the same boost pressure. Change to a less efficient intercooler (say, FMIC to TMIC) to see what effect it would have on your horsepower for the same target boost, etc.

Updated to v2.1
Made a couple of changes, renamed some of the fields a little bit, and added an input for the compressor inlet temperature (lets you account for intake temp rise due to a short ram intake, etc.).

Updated to version 3.0

I've added a new tab called Fuel Line Sizing
With the recent trend of fuel line/rail discussions on NASIOC, I decided to add the calculations for determining the pressure drop through your lines/rails, along with the connections and line length between the R/L bank of injectors (for a series rail setup) to calculate the AFR difference between the first and last cylinder to get fuel.

It's currently set up for a stock line/rail config on a single Walbro 255, so you can adjust as necessary, see the effect of going to a Bosch 044, DW300, or dual Walbro 255 on the stock lines, etc.

There are references at the bottom of the table to give you the values for the density and viscosity of gasoline and E85, and example line roughness values for stock lines (grossly approximated, though it doesn't make a huge difference) and aftermarket teflon lines.

Unfortunately the vast source of info and equations I had for the BSFC/power calculations aren't available for the pressure drop through lines, so I had to go back to the textbook fluid dynamics equations for liquid flow through a pipe given the Reynolds number, turbulence, wall roughness, etc. So let me know if you run into any problems with the calculations.