larger injectors and pcm calibration

[Craig 94 TA GT]

I just talked to someone from Racetronix because I want to purchase thier flow matched 28# injectors (@ bar 3). However, the representative told me that I need to recalibrate my PCM for the larger (flow) injectors or the driveability and mileage will be affected. Firstly, will just a 4# increase need this? Secondly, if I do need recalibration, do I need LT1 edit? Thanks.

[Craig 94 TA GT]

I think I'll answer my own question here by saying I do need to reprogram the PCM. However, I still cannot verify the actual flow rating on these injectors (p/n 12561462). Racetronix insists it is 28 lb @ 43.5 psi. Here's the web page even... http://www.racetronix.com/Racetronix...12561462R.html
Yet, I've never seen or heard about an LS1/LS6 injector flowing this high of rate at 3 bar. They're supposed to be off of a Z06, but I can't find any additional info. A seller on ebay claims these are 28.8 at 4 bar. So there are different #s.
If anyone has anymore info on these injectors, I would greatly appreciate it. I really need to know because when I get my PCM reprogrammed, I wouldn't want to give wrong figures. Thanks.

[Injuneer]

The base LS1 fuel system runs t 4 bar (58psi). Not sure what the Z06 runs at, but it would seem odd to lower the fuel pressure for a higher performance engine. But.... if they are off a Z06 (the website does not indicate that), they most likely would have been flow rated at well above 28.8#/HR in a 405HP Z06. GM is VERY conservative on injector sizing. They used 28# injectors in the LT4 which had nowhere near 405HP. If these were 33.2# Z06 injectors (I do not know if that is the Z06 size, just back calculating it), when you reduce the pressure to 43.5psi, they would flow 28.8#.

You need to confirm this with "Jack" at Racetronix.

[Craig 94 TA GT]

Thanks for the reply Fred. The only place I found info on them is ebay. Most who list injectors with that part number claim they are off a Z06. By the way, I checked standard LS1 injectors and they are a different part number (p/n 12554271, 12456154, and 12482704). None match the p/n of the "Z06" injectors. So I still can't find another place to verify the flow rate. The only thing I've read is that the Z06 has higher flow injectors than the LS1 Vette, but I don't know how much larger.

[Racetronix]

Z06 who?

In 2002 GM dropped the Z06 injector from 28lb to 24lb (@300KPa).

You can not use a Z06 as a means of identifying and injector!

Most injectors are rated at an engineering standard of 300KPa / 43.5PSI. If a manufacture decides to run an injector at a higher or lower pressure to achieve their fueling requirements this does not change the rating at 300KPa / 43.5PSI.

[Craig 94 TA GT]

What I don't understand here is that most people say that the LS1 type fuel injectors are rated at 58 psi. Thus, the LS1 injectors flow less than the LT1s if this were true. In fact, I have heard a few people installing the injectors (p/n 12561462) in their LT1. They said that they are rated at 24 lb/hr in our 43.5 psi. All of them installed them without PCM recalibration and it works perfectly according to them (fuel mileage, throttle response, etc.). That is because they say that the lb/hr rating is exactly the same. That alone makes me question the flow rating on these injectors. Thanks.

[Jeff_in_Atl]

I've been reading all of this thread because I will probably need it one day but here is my thought. Wouldn't the computer compensate for the injector flowing more or less to a certain degree? I can see it not being able to if it is way bigger or smaller. I would think that if is close, it wouldn't matter once it gets in closed loop mode. Would it matter when it is warming up in open loop mode?

As for the flow rate question, I would think the flow rate would be fairly linier based on the pressure. For example. At 0 PSI it puts out 0 lb/hr. At 10 PSI it will put out 5 lb/her. At 20 PSI it will put out 10 lb/hr. At 30 PSI it will put out 15 lb/hr. etc etc etc. (ignore the values I used. It is just to make a point.)
At PSI = you get LB/hr with 1 model injector
21.75 = 12
43.50 = 24
65.25 = 36
87.00 = 48

[Injuneer]

The computer can adjust for flow differing from what is programmed into the PCM, but its not a wise idea to run that way.

First, the computer has limits as to the amount of "correction". If you put in an oversize injector, and don't tell the PCM, it can only correct by removing a maximum of 15% of fuel (108 BLM). That means if you put a 30# injector in there, and left the PCM constant at stock (24.9#/HR), the PCM could only reduce the fuel flow to the equivalent of 25.3#/HR using the long term corrections. So it would run rich in "closed loop".... part load, part throttle.

Then, at WOT, because the PCM was "pulling fuel" in closed loop, when it went to WOT power enrichment mode, it would ignore the BLM's and the engine would be running with 20% too much fuel... or WAYYYYY rich.... enough to damage things.

As far as flow, it is definitely NOT directly proportional to pressure. It is proportional to the SQUARE ROOT of the pressure. It follows the "orifice equation". That means....

Lets say you have an injector that has been measured to flow 30#/HR at 43.5psi. If you run it at 58psi, the calculation becomes:

30#/HR * (58 / 43.5) ^0.5 = 30 * 1.333^0.5 = 30 * 1.155 = 34.64#/HR.

Some multipliers for an injector rated at 43.5psi:

20psi - 0.678
25psi - 0.758
30psi - 0.830
35psi - 0.897
40psi - 0.959
45psi - 1.017
50psi - 1.072
55psi - 1.124
60psi - 1.174

[Jeff_in_Atl]

I found this equation.

Po=p+.5pVē+pgZ

Po=stagnation pressure
p=pressure in moving fluid
V=velocity
p=density
Z=altitude
g=gravitational acceleration

Fred's looks easier. LOL
Sounds like the easiest thing to do is get what you want and get an editor like LT1 edit and change the table for the new injector.