Injector Sizing Spreadsheet

whittlebeast · Post by **whittlebeast** » Sun Dec 25, 2005 5:18 pm

I have been working on an Excel worksheet for calculating the size of injectors. In resurching the math required, I have stumbled on a few quirks the MS brings into the equation that most formulas appear to ignore. Have fun playing with the worksheet and notify me if any apparent errors are found. The other sheets have info and data that I have found over the years that may prove very helpfull.

see http://www.ncs-stl.com/fuel/ReqInjectors.xls

Please look close at the following section as it gets a little confusing.

1 for Alternating Pulses or 2 for Simultanious Injection Pulses____1
Injections Per Cycle_____________________________________2
Actual Injections Per Cycle for each Injector__________________2

AW

Post by **efahl** » Sun Dec 25, 2005 5:29 pm

I've been playing with Andy's spreadsheet for a couple days and it does a much better job of injector sizing than anything else I've ever seen (I'll be stealing his formulas for MT's injector size calculator). Note also that he's doing throttle body size estimation, so this is an exceptional piece of work for people starting from scratch.

Eric

daxtojeiro · Post by **daxtojeiro** » Tue Dec 27, 2005 12:17 pm

Excellent work Andy, is there an optimum speed for air intake? 58MPH is what I get with 8 throttles and 166MPH with my original single throttle,
Phil

whittlebeast · Post by **whittlebeast** » Tue Dec 27, 2005 1:20 pm

If HP is your goal, at the cost of drivability, then I like to shoot for 70 MPH or less. Run this sheet based on a high strung Japanese motorcycle and you get speeds of like 40 MPH. You also start seeing a second set of servo controled throttles to (I assume) control traction/throttle repsonse/HP.

The real solution is hugly progressive throttle bodies.

AW

daxtojeiro · Post by **daxtojeiro** » Tue Dec 27, 2005 1:37 pm

Andy,
cheers for that, so at 58MPH its going to be undrivable??

Phil

whittlebeast · Post by **whittlebeast** » Tue Dec 27, 2005 2:31 pm

No not undrivable, just sporting

old-colt · Post by **old-colt** » Tue Dec 27, 2005 4:59 pm

Very nice work Andy,
This program has answered some questions for me and opened up more.
I like the estimated airspeed in the intakes. How hard or accurate would it be to estimate peak intake runner velocity?
This is a great and useful tool.

deepnsteep · Post by **deepnsteep** » Tue Dec 27, 2005 10:24 pm

Andy,

I think there may need to be an if statement added to the "Actual Injections Per Cycle for each Injector" cell. If I select 2-stroke, simultaneous, and 3 squirts per cycle (3 cylinder), it shows 6 events per cycle. That way, I get like 300 lb/hr injectors..........

It's still pretty suprising how much difference there would be between 3 squirts and one squirt per cycle (if I divide actual injections by 2)......about 23 lb/hr diff! Is that reasonable?

Great tool Andy!

Levi

whittlebeast · Post by **whittlebeast** » Wed Dec 28, 2005 4:12 am

Thats the part of the math that messes with my head and I am not convinced I have that math correct. It's possible that the flow rate calculations are correct but I have the cell "Actual Injections Per Cycle for each Injector" miss labeled. It may need to be "Total number of injector opening events per engine cycle but I need to devide by the number of injectors/injector drivers. Any help with the math is welcome. The reason that I did this in the first place is I kept getting confused.

With a high reving two stroke, you realy can run out of time real fast.

AW

whittlebeast · Post by **whittlebeast** » Wed Dec 28, 2005 5:41 am

Ok, Try this one. The default sample is a simple (2 stroke) motor to understand. Change one thing at a time and see if you can catch it in error.

see http://www.ncs-stl.com/fuel/ReqInjectors02.xls

Thanks for the help

AW