cardzrule

How come ur trying to get every1s email? Somethings fishy here dood.

DCrosby

I don't disagree with pistonsuk, except for the name of his login, but doesn't Barometric pressure go into this, since most of the FD's need a barometric pressure sensor on the ecu, to be able to tell how dense the air it's reading pressure for, through a MAP sensor, is.

Or are we talking about a MAF system ??

Howard Coleman

iTrader: (6)

FWIW

i have used the following relationship for a number of years to correctly size my turbos.

1.92 cfm = one rear wheel rotary hp. that's maximum and fully optimized tune.

from roger mandeville and it was empirically derived. you of course are free to pursue your own method to get to the relationship.

using the above relationship i correctly sized my twin TO4s that i run and it has worked out on the nose. 82 lbs per min = 620 rrwhp. another commonly used method is to take lbs/min times ten to get piston rwhp and then divide by 1.3 to get rotary rwhp.

works for me.... probably done the calculations over 1000 times.

howard coleman

pistonsuk

Yes, but indirectly. That is the beauty of this calulator. All that is necassary is:

1)fuel flow
2)AFR

The baro pressure, VE, air density etc... is all taken into account by the more complex algorithims of the ECU. The ecu uses all of this variables as inputs to determine the fuel flow (output), which is then used as an input to the calculator. So no it does not be put into the calulator directly because the fuel flow has already taken this into account.

If someone disagrees please post your reasoning but other than:

1) boost leaks
2) accuracy of the flowrates of each injector and
3) accuracy of your AFR gauge

I dont see what this calulator does not tell the exact mass flowrate of the engine. This is a big step considering most calculators rely on an estimated VE or some form of emperical data.

Justin

cardzrule

Like i said before you cant calculate teh amount of air if you dont know teh weight of air or fuel. Hot air weighs less than cold air, boosted air weighs more then na air, hot fuel weighs less than cold fuel, humidity and altitude changes teh weight of air somehow that Im not too sure about. It aint gonna work dood. All ur gonna get is a guessed weight of fuel and a pretty good afr but aint no way to guess teh airflow coz you dont know teh air weight. If you wood post a sample insted of asking for every1s email then you can maybbe see what Im saying.


This makes more sense 2 me xcept I dont understand teh 1.3 thing. Prob right tho xcept maybbe high boost or porting gonna be different coz of efficiency of bsfc. Maybbe also depends on tuning coz aint no way normal peeps can tune as good as teh pro drifter crewchiefs who are gonna make more hp.

When you did this 1000s of times did you have about teh same porting and boost or way different porting and boost in different engines?

pistonsuk

Let use these numbers posted by cardzrule:

Inj Duty 80
RPM 5000
Boost 10
AFR 11

Inj size 550 (@43.5psi) (~ 52.5lbs/hr by using an online calculator or

550cc/min x 1000kg/m^3(density of water @22C) x 0.719 (SG of gasoline) x 1m^3/1000000cc (converting m^3 to cc) x 60min/hr (converting min to hr) x 2.2lbs/kg (converting kg to lbs) = 52.19 lbs/hr

Static fuel pressure 43.5
Number of injectors 4

There is no need for fuel flow correction due to the static fuel pressure being the same as the pressure at which the injectors were rated at.

Therefore the total mass fuel flow rate through the engine is:

Fuel Flow = 4 x 52.19lbs/hr x 0.80 = 167lbs/hr

The AFR is a mass ratio of air to fuel therefore the total mass airflow rate though the engine is:

Air Flow = AFR Ratio x Fuel Flow = 11.0 x 167lbs/hr = 1837lbs/hr

or:

1837lbs/hr x 1hr/60min = 30.62lbs/min

Make sense yet?

Justin

cardzrule

ok first off ur just guessing at teh fuel weight. Maybee Im using fuel thats 0.74 SG - you dont know. Also you dont know teh temp is 22C. Maybbe its hotter or colder - you dont know.

Makes total sense - but there aint no way to figger cfm from that without more info coz you dont know how much teh air weighs per CF. That 30.62lbs/min could be lots of cfm trough teh rotors or maybe not so much cfm depending on boost and temp and other stuff. Make sense yet?

^ lbs min maybbe if you guess at fuel SG and temp and that stuff you said that could mess up the calculations, but not cfm dood. Sorry. Pretty cool math neway.

pistonsuk

No I'm not guessing the weight. This is a measured value.

If you know your fuel is a different density then that could be used in the calculation. Even if the 0.719 was used instead of the 0.74 the overall result would be off by 0.85lbs/min. Would this kind of error change your decision of what turbo to select?

Like all liquids I know of, the density is so nearly constant with respect to temperture is would be hard to measure it otherwise. Especially over a temperature range as small as 50F or so. Again if it was to change by 2-3% the overall calulation would only be off by 2-3%; not enough to make you decide on a different turbo.

This is just wrong. The mass flow generated from this calculator can be changed to a CFM at any pressure and temp. What is the need for this? If you wanted to find the CFM of the engine then use the boost pressure and intake temp. Garrett turbo maps are lbs/min (mass flow). The Garrett turbo maps are corrected for standard temp and pressure. This is included in the calculator by using the same assumed pressure in the intake (before turbo) tract of 13.95psi and the calculator does ask for ambient temp.

rrussell

I agree. I did a study on the coefficient of volume expansion of petrol and found the changes were so small that the regulators altered the data a ton more then the expansion of fuel.

I was at the time trying to figure out why some nitrous engines were going lean and my thoughts were that the fuel expansion was the problem. But in the end it was the regulators reacting with the heat from the engine compartment.

But anywho nice work!!! I see where your going with this and I think your on the right track.

I too have a piston engine spreadsheet I use for tuning and a rotary spreadsheet.

It will give me the info I want by the use of a engine dyno or chassis dyno to set my fuel cells to the desired A/F ratio quickly.



Here are the instructions for my spreadsheet for piston type and a prt/scr pic.

Spreadsheet Instructions

Line 1
Enter engine Size in Cubic Inches.

Line2
Enter RPM.

Line3
Enter PSI This is how much boost at the intake.

Line4
Enter Elevation PSI. This is found on Sheet 2.
Just add two zeros to the number column on the left.
Example line 8 would be 800’ line 60 would be 6000’

Line5
Enter Intake Air Temperature.

Line6
Enter the size of injector in lbs/hr.

Line7
Enter VE. This depends on the head. Built heads will usually have 1.0 or 100%
Stock can vary from .85 to .90

Line8
Enter how many cylinders.

Line9
Enter air fuel ratio. This should be known by the use of a W/B.

Line10
Enter Brake Specific Fuel Consumption.
This will vary on the type of engine and how efficient it is with its fuel.
Also rich air fuel ratios will have a higher numeric value.
Example: 10.5 A/F on a D16 will be around .65BSFC 12.8 A/F would be around
.5 BSFC

Line11
Enter vehicle weight.

Line12
Enter the original pulse width or duty cycle that needs to be change to target
pulse width or duty cycle.

Line13
This is what you want you’re A/F ratio to be.

Line14
This is what your actual A/F ratio is seen by using a W/B.

Line15
This is what you would change your pulse width to or duty cycle.

On the right side there is Liters conversion to cubic inches.

CC/MIN is to convert cc/min injectors to lbs/hr.

Under the “J” column is where you can tell what the equivalent injector would be by
adjusting the fuel pressure.

LBS/HR in red is what the injector was converted to in lbs/hr.

CFM in red is the CFM of the engine.

Lbs/min in red is what the engine is flowing in lbs. I use this for turbo lbs/min flow also.

M/S MAX in red is the maximum amount of time available the injectors can stay
open in milla. seconds before the next cycle.

Duty cycle in red is what the duty cycle is with the inputs you entered.

P/W in red is the pulse width that the injector will be open to achieve the A/F ratio that you entered.

Hp in red is Hp at the flywheel. To determine WHP you can calculate on a know drive train application.

Torque in red is torque at the fly wheel.

E.T. in red is a approximate time this vehicle at this weight and HP would run in the ¼

MPH in red is a approximate mile per hour this vehicle would run in the ¼

%CHANGE in red is used for VE tables for making changes by percent.

Black cells are descriptions.

Red cells are the outputs based on the Blue cell entrees.

Blue cells are where you enter your values.

I recommend you just start entering your own cars values and make changes to see what happens.
This will teach you a ton about what each change does to the engine and its output.
Keep in mind this is just another tool for tuning. I always recommend running a W/B and start
out on the rich side.

pistonsuk

Nice work yourself. If you want to take a look at mine go to the single turbo section and download it. You only need ambient temp, inj duty and AFR to calc corrected airflow rate. Let me know what you think.

Justin