RomRaider

This is my first spreadsheet to help people out

Nothing spectacular, just a basic spreadsheet using various formulas to calculate compressor airflow for estimated HP (thanks Garrett) and BFSC - as well as provide a list of turbos from various manufacturers.

Screenshot:


How it works:
Enter the required information:
AFR = rated Air/Fuel ratio for max power (not your AFR at max power, but the fuels rated afr for max power)
injS = injector flow in cc @ 100% IDC (static flow)
IDC = injector duty cycle
WHP = current wheel horse power (use Airboys spreadsheet for best results)
DL = drivetrain loss
inj# = number of injectors

And it will calculate:
injF = calculated injector flow (cc) @ IDC
lbsF = calculated lbs of fuel used per hour
HP = calculated horse power (crank)
BFSC = lbsF/HP

With these calculated values, the spreadsheet uses Garrett's formula to calculate compressor airflow for estimated HP:
Wa = HP*A/F*BSFC/60
Wa = Compressor Flow
HP = Horse Power (crank)
A/F = rated Air/Fuel ratio at max power for fuel used
BSFC/60 = Brake Specific Fuel Consumption, divided by 60 to convert to minutes.

Now work out what HP you are after (be realistic), then using the airflow beside that HP, find a turbo that can support that airflow. All pretty simple, but can be quite useful





If you spot a mistake, please let me know so I can assure it is as accurate as possible.

Regards
Leslie

Cool. I made something similar a couple years ago. It might help you improve yours a touch because mine has inputs for temperature, pressure drop, etc.

http://www.bescaredracing.com/sti/turbo ... ksheet.xls

t

Cheers mate. Will have a looksy on the weekend.

Eventually I hope to incorporate compressor map plotting and more inputs etc, and do it all in php, but for the moment I'll keep it simple until I have more free time

Leslie

A little off topic:

The VF52 would be around 35 lb/min?
And the VF48 a bit bigger? 36?

As far as I know, the VF52 uses the same compressor wheel as the VF48. The differences are elsewhere.

Aha, and that would be +/- 35 lb/min?

Where is the information from for compressor size? Also, if you want to add the HTA68 its 47 lb/min.

I don't specifically list the compressor wheel size as it is not that important compared to actual measured airflow of the compressor, which is why airflow is listed.

I will update the spreadsheet (sometime this week) with some of the more recent turbos that are not already in the list of turbos and post the new revision once done.

Leslie

you sure those whp numbers are correct? I don't even think with E85 I could get my 18g to 425+awhp

Actual WHP possible from a specific airflow is totally dependant on the other variables in the spreadsheet - also the WHP value is derrived from the BHP value.

If you get the variables correct, then the BHP indicated is mathematically correct.

Engine volumetric efficiency appears to be an uncalculated variable in this spreadsheet based on my calcualtions. The Lb/min calculation based on turbo airflow appears to be correct though

I have an old calculator I developed floating around somewhere on an old hard drive, that maps rpm in 600rpm ranges which can also show boost threshold.

To give you an idea, the plot graph overlayed over a Garrett GT2871R 52T turbo with 88% to 94% V.E varying over rpm based on existing tune on 2.85L capacity(two of these turbos on a Chev 5.7L LS1 motor)



Boost threshold was 1800rpm with peak rpm being 6000rpm. Peak engine torque went right through the middle of the compressor islands for optimal airflow temps etc.

I made my own with some static values to see if I wanted to upgrade my turbo. I'll try and make some changes. I'll incorporate BSFC as I just have it set for gas and E85 right now.

This is the turbo I was planning on getting:



This is the calculated powerband for the 60-1 and CHP, WHP, etc:

[url=http://www.flickr.com/photos/gabedude/5577546920/]

This is my current 20G if I add an external gate (the peak power is the same as previous results, but adding the external gate will allow me to get more low end TQ):



I am sticking with the 20g.