Flow Rate vs KPa Table

[jaxjack]

Thanks for your patience up front and your advice. I just supercharged my 4.8 Silverado and have purchased the 8.1L injectors P/N 17113739. These are the recommended injectors for this app and are rated at 44 lb/hr @ 58 psi for this app. Multec says these injectors run 43.82 lb/hr @ 58 psi or 4.97 g/s.

My question is what to put in the Flow Rate vs KPa Table? Start at 0 inches of vacuum at 43.82 and progress at the same ratio of increase as the current table shows? Thanks!

[blownbluez06]

I can tell you that you want to get it right, because the VE table runs off of this and if you get it wrong, you will have to go back and change the IFR table and then start over on your VE table.

This is something EC_tune posted for someone with 42lb Lucas injectors. It is close.

Here's the IFR I generated with Lucas 42's on an APS TT:
48.48824 48.79827 49.10830 49.41832 49.72835 49.97637 50.28640 50.59643 50.84445 51.15448 51.46450 51.71253 52.02255 52.27057 52.58060 52.82862 53.13865

I calculate that your 43.5lb injectors are 3.45% larger than these if the lucas injectors are truly 42lb compared to yours. Hopefully someone will chime in and give their .02.

[EC_Tune]

What year is your truck?
If it's 04 or later you have a returnless system:
43.83784 44.08586 44.33388 44.64391 44.89193 45.13995 45.44998 45.69800 45.94602 46.19404 46.50407 46.75209 47.00011 47.24814 47.49616 47.74418 47.99220

If 03 or earlier use 43.82 across the board.

[jaxjack]

Thanks so much for the input. My truck is an '01 with return but the table for the stock 24 lb injectors reads the following:

Labels 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Flow 41.54365 41.85367 42.10169 42.34972 42.59774 42.84576 43.09378 43.34180 43.58983 43.83785 44.08587 44.33389 44.58191 44.82993 45.07796 45.32598 45.51199

That is why I do not know whether to insert the same number across the board or input data vis a vis a ratio as the above shows. Comments???

[EC_Tune]

Yep, same # across the board with a return-to-tank system as the vacuum/boost will regulate the pressure across the injector. The sloped IFR is for those vehicles with returnless systems.

[jaxjack]

spaceeba super tuner. will give that a go.

[Fast240Z]

I have these same injectors in my suburban and I used 37.95 lb/hr for my tune and it has worked fine. The reason I used this number is because my idle fuel pressure is 43.5 psi. I have a return type system which raises the fuel press to around 55psi. under full boost. Have I missed the boat on the tune entry? What would be effected if I change the value to 43.82 lb/hr?

Mark

[EC_Tune]

should be correct for your fuel pressure.

[Fast240Z]

should be correct for your fuel pressure.

The number I am already using or the other one? Not sure which you are saying is correct.

Mark

[EC_Tune]

The number you are using.

[jaxjack]

after having set my new injectors to 43.84 the truck seems to run okay, but the afr is pretty lean through a lot of the operating range. I, too, am going to set my base number to 37.95 since my idle fuel pressure matches your suburban and see what I get. Will report back results....

[jaxjack]

went back in and set the numbers to 37.95 across the board, cranked 'er up and all the numbers fall perfectly into line!!! I have 14.6/14.7 afr at idle and under load the afr numbers go from high 11s to about 13.8 or so. Thanks for the input. This is fun!

[Fast240Z]

I guess I will be leaving mine alone then. This is fun! It is nice to know we can figure out things and make changes just like they did 30 years ago when they just turned screws on carbs.

Mark

[EC_Tune]

Glad you guys figured everything out.

[BINNCZ71]

Want to double check my settings:

Truck is 99 Silverado with 5.3 .. Truck has 02 pcm and 02 Injectors.
What should flow rate be set to?

[Billf6531]

Yep, same # across the board with a return-to-tank system as the vacuum/boost will regulate the pressure across the injector. The sloped IFR is for those vehicles with returnless systems.

A friend has a 98 C5 with a return-to-tank fuel system. The stock IFR table is populated with increasing values from 0-80 KPa. If I understand your comment correctly, shouldn't the factory setting be the same value in each cell?

Stock table is attached.

[EC_Tune]

It should but the C5 isn't referenced to manifold pressure it's referenced to ambient pressure inside the air bridge. I have no idea why though....

[ElecTech]

Its just to compensate for Baro. changes. The "regulator" also works as a pulse dampner. So I've read.

[kevmar]

I have the 8.1 truck injectors rated at 31lb/hr I came up with 29.89 is this correct. its on 01 truck as well, its hard to start up and is real rich, after running its fine, well still smells rich even though ltft are saying 0.0 and shorts are going from -.2 to +.2

[EC_Tune]

Did you use all the injector settings from the 8.1L truck? They are correct.