Injector scaling question. Which rate to use

[ViolatorTA]

I'm about to install my Racetronix 42lb injectors while finishing up my H/C swap. What I need to know is which figures I should enter into redhard's injector XLS spreadsheet. Racetronix's site rate the injectors at 43.5 and 58lb fuel pressure.
From their site

Part Number Delphi 01D030B (Lucas old 5208009, Lucas New 621031, Delphi old D3181AA)
Static Flow Rate: 42.29 lb/hr @ 43.5PSI (300kPa) or 320gm/min
Static Flow Rate: 48.83 lb/hr @ 58.0PSI (300kPa) or 370gm/min
Dynamic Flow Rate: 9.96 gm/pulse - 2.5ms pulse width and 10ms repetition rate @ 43.5PSI
Coil Resistance: 15.9 Ohms / High Impedance / High-Z (No ECM driver modifications required)

This would be for a 1999 Trans Am. I was thinking I need to use the 48.83@58lb since it's an LS1 but want to be sure.

Thanks in advance
Shawn

[eboggs_jkvl]

Usually, you use what it is rated at out of the box and that is 43.5. You then tell the spreadsheet that you are running 58 PSI, the "size" of the injector and it calculates the rates for you.

Elmer

[joecar]

Static Flow Rate: 42.29 lb/hr @ 43.5PSI(300kPa) or 320gm/min
Static Flow Rate: 48.83 lb/hr @ 58.0PSI (300kPa) or 370gm/min
Have you noticed this: 48.83/42.29 = sqrt(58.0/43.5)

IOW... both sets of values are identical.

You can use either set in the spreadsheet, it will give the same results

(your fuel rail pressure will be 58 psi, might be a good time to measure it).

[ViolatorTA]

Thanks. I'll be sure to bring my pressure guage home from work and measure the pressure. Would the stock pump suffice for now or should I look at picking up a better pump sooner? Just installed AS 5.3 heads and TSP 231/237 cam but used the stock injectors until I knew what to use in the spreadsheet.

[joecar]

Check your injector duty cycles when your LTFT's are zero;
if at WOT high RPM the DC hits/exceeds 100% then you're out of injector (say 80% to give you some room).

[Black02SS]

Like joe said, check the DC. I am not a fan of it really to be honest. I use it on certain vehicles, but have ran H/C 346's all day with 28lb to 30lb injectors with no problems. The 42lb injectors will last you for a LONG while. I did a 383 with a decent size cam that did over 500 to the wheels. Duty cycle was only about 70%.

[ViolatorTA]

thanks for the advice. I plan to run a 150 dry shot on this once I get it installed and have more understanding of tuning it. I just hope scaling the injectors with the spreadsheet doesn't mess things up from where they are.

[Black02SS]

If you are going to run a dry shot I would instal a new fuel pump then. Make sure you also look at the DC then. This is one of the times I believe in looking at the DC. Play it safe and have fun. :)

[joecar]

From the various books I've read about NO2, you don't want to go lean while spraying, so it may be wise to install bigger injectors with the bigger fuel pump.

[Black02SS]

With a fuel pump I think you will be close on the 42's. They should work though for you as long as you don't get crazy with the nitrous.

[eboggs_jkvl]

My 42s ran out of steam around 450 RWHP. Be careful on your A/F with the 150 shot. Aftermarket fuel pump is vital.