radix power

[zippy]

you're saying the fuel pressure is better when the regulator was seeing boost? this may be something i need to try.

[Nightshift]

Excellent thread ! ! !

Though allot of it goes right on over my head....

Nice we have people out here that know what they're doing.

Since I took some time to read, it's making sense.

Maybe one day I can be technical...

 

WW

[hellbents10]

That was a nice little bit of info big tex. This thread is rockin out!

[misterp]

That was a nice little bit of info big tex. This thread is rockin out!

[BigTex]

Exactly Zippy. Under idle vacuum, the fuel pressure regulator lets off some pressure from the standard 58psi. Under boost, its opposite, almost like a FMU. The boost pressure forces the regulator to higher fuel pressures. This would be valid on 99-03 trucks with the regulator on the fuel rail.

 

You can test this with tuning software. At normal operating temps, log the LTRIM values at idle. Pull the fuel regulator vacuum tube off. Trim values should go more negative as it should be getting more fuel pressure. On my truck, when it was hooked to the plugged up default fitting, it made no difference in fuel pressure or Trim values by hooking / unhooking that vac hose.

 

Tuning wise, the 99-03 trucks have a constant fuel injector flow value. The 04+ trucks, which don't have vacuum regulated fuel pressure, have scaled fuel injector flow rate based on MAP. In essence, fueling for each type should equal out with one manually varying fuel pressure to MAP pressure, the other adjusting its calculated fuel needs based on MAP. Now under boost, the 99-03 trucks get the benefit of higher fuel pressures due to boost. The 04+ vehicles don't.

 

Overall, at WOT in the high rpms, I probably have 15-20% higher fuel pressure with the regulator hooked up properly than not. That makes a big difference in tuning and fueling needs.

[SSLink]

So on the '04-up's fuel pressure is scaled by the PCM directly from MAF readings while on the earlier models it's vacuum regulated? Am i getting that right? Interesting.

 

Zippy: have you tuned many Radixed '04's? In your experience are they experienceing the same issue of loss of fuel pressure in the upper RPM's or are they keeping better pace?

 

This has been a very interesting thread. Thanks to all you tech and tuning gurus.

[zippy]

the truck we put the 2.8 pulley on is an 04'. he's coming back this week.

[H2Racer]

I installed the magnacharger fuel pump voltage booster yesterday afternoon, and went out for some log runs. I'll have some interesting findings to post a little later today. I'm still typing them up and double checking my work. I want to be sure everything I say is true and clear.

[BenKey]

So when are bigger injectors being tried?

[stexx]

the fuel pressure is also regulated by the PCM on the 03's

[BenKey]

the fuel pressure is also regulated by the PCM on the 03's

<{POST_SNAPBACK}>

Not sure if that is true. If it is, I be damn if I know where you control that in edit.

[H2Racer]

I hooked up the magnacharger fuel pump voltage booster today. What I found out was not all that I hoped to see.

 

I'll remind that I have an LQ4 in my 2004 H2 and I'm running a Radix with a 2.9 pulley and the Walbro in-tank fuel pump.

 

I believed I would connect the booster and see my injector time constants drop from the 22.8-23.0 ms time constants that I was seeing at high rpms. I expected to see this because I have been assured time and again by many people on these forums that 42 lb injectors are enough to support more hp than I'm making. Theoretically, the fuel pressure was dropping off and that was making the injectors hang open longer to deliver the necessary fuel.

 

I ran back to back runs with both wideband and HP Tuners logging. Here’s what I found…

 

WITHOUT the voltage booster I saw the following-

 

1st gear- AFR: 11.0 - 12.6

Airflow: 455 g/s and 59.4 lbs/min @ 5950 RPM

 

2nd gear- AFR: 11.0 - 12.7

Airflow: 451 g/s and 59.4 lbs/min @ 5940 RPM

 

 

WITH the voltage booster I saw this-

 

1st gear- 10.9 - 12.1 AFR

Airflow: 460 g/s and 60.68 lbs/min @ 5970 RPM

 

2nd gear- 11.0 - 12.1 AFR

Airflow: 464 g/s and 61.26 lbs/min @ 5907 RPM

 

 

Now what does this all mean? Well, the voltage booster helped out a great deal in that it knocked my AFR back down to a "safer" level on the top end. This gave me more power and therefore more air consumption. I consider it to be a good product that performs as advertised.

 

Well, when I dig a little deeper into my logs I still see that I've got 22.8 -23.0 injector constants on the upper RPM's (5600 and up). That’s the EXACT SAME constants I had before the pump was added. This shows that the injectors are NOT really big enough to support the power level I'm at. They should not be working that hard with good constant fuel pressure if they were sized appropriately.

 

Yes, I can and will run this until I can upgrade, BUT it is not optimal and I can't safely and reliably go to a 2.8 or smaller pulley without the potential of going seriously lean again.

 

The pump is enough and the voltage booster assures rock solid fuel pressure at the rails. However, the injectors are still too small as evidenced by their continued excessive open time constants and the fact that they cannot maintain the commanded AFR. I know that 60 lb injectors would make more power on my combo as it sits, because my combo makes best power at the 11.0 – 11.4 AFR range.

 

So to go back to the original question… “Are 42 lb injectors big enough for a engine pushing MY airflow numbers?” NO, they are not big enough. If they were they wouldn’t have to exceed 20 ms time constants at 6000 RPMs, much less below. Ultimately it looks like it’s more about the airflow level you are seeing rather than simply what engine and what pulley. Blanket statements that the 42 lb injectors are or are not enough are worthless without more information.

[BigTex]

So on the '04-up's fuel pressure is scaled by the PCM directly from MAF readings while on the earlier models it's vacuum regulated? Am i getting that right? Interesting.

 

Not quite. Its based on manifold absolute pressure (MAP), you said MAF which is mass air flow.

 

A little more in depth answer:

 

Our reference for measuring pressure is the earths atmosphere. 58psi is our default fuel pressure, but thats in reference to external atmospheric pressure. At idle, our vehicles build up vacuum pressure in the manifold. Our PCM calculates its fueling based off the amount of fuel an injector can flow over a given time. At idle, the injector is under vacuum pressure from the manifold on one side and has fuel pressure pushing from the other side. That vacuum basically increases flow by sucking fuel out when the injector is open. This is common to both truck setups.

 

On the 99-03 models, the fuel rail has a pressure regulator that bleeds off excess fuel to keep pressure at 58psi at one atmospheric pressure. It has an internal mechanism that connects to the intake manifold which allows a lower fuel pressure when under vacuum at idle. That lower pressure is in direct relation to the added fuel flow gained from being under vacuum. Basically that means that even though the injector is getting increased flow from vacuum pressure, its also getting lower fuel pressure (and less flow) from the regulator. This should equal out for a constant fuel injector flow rate. When the throttle is opened up, the manifold isn't under vacuum and the regulator increases fuel pressure back to 58psi.

 

On the 04+ models, the regulator isn't hooked up to the intake manifold, so it doesn't see any vacuum (or boost). That means its always flowing a consistent 58psi. To compensate for the added injector fuel flow when under vacuum, the PCM is told it has larger injectors for different levels of manifold pressure. Relying on the MAP sensor, the pcm knows how much vacuum the truck has at idle. It uses that value to adjust the injector flow rate in fuel calculations. This allows the proper amount of injector fuel under vacuum or WOT. The end result is consistent fueling.

 

The 99-03 way is a manual workaound for vacuum increased fuel flow rate and the 04+ way is an electronic calculated workaround. Both ways work fine. But when adding forced induction to the mix, the 99-03 fuel pressure regulator acutally raises pressure above 58psi allowing more fuel flow. The 04+ system cannot compensate in this way, and if it did, it would just calculate it in as a small injector. So it would be more likely for a 04+ truck to run out of injectors than an 03 under boost.

[BenKey]

I still have some (700 miles used) 60lb injectors. Summitt has sets of new connectors for $15.

 

Richard - great stuff

[BigTex]

I hooked up the magnacharger fuel pump voltage booster today.  What I found out was not all that I hoped to see.  I have a 2004 H2...

Increasing voltage on an in-tank regulated fuel pump will only keep fuel pressure up, but not increase it any. Any additional fuel flow from the over-driven fuel pump is immediately released back into the tank by the regulator.

 

 

I believed I would connect the booster and see my injector time constants drop from the 22.8-23.0 ms time constants that I was seeing at high rpms.

You would not see any less injector time constants unless you made a programming change. Just increasing fuel flow or adding larger injectors wouldn't alter the PCMs injector calculations unless you changed some values in the tuning. It would still open the injector the same amount of time, but you would see a difference in the AFR.

 

 

Airflow: 455 g/s and 59.4 lbs/min

Airflow: 451 g/s and 59.4 lbs/min

Airflow: 460 g/s and 60.68 lbs/min

Airflow: 464 g/s and 61.26 lbs/min

Thats interesting. Who did your initial tune? The stock MAF table scales up to 454 Grams/Second at the highest value, which corresponds to 12000Hz raw MAF data. You should not "see" or log anything higher than 454g/s or 59.9 lbs/min unless your MAF is scaled differently. What you can do is log the MAF Hz which will still increase beyond 12000. The PCM won't be able to calculate a flow rate for anything higher since thats top of the table.

 

 

 

Blanket statements that the 42 lb injectors are or are not enough are worthless without more information.

I think you are right here. Zippy didn't state he was working on an 04 truck until after I made my first post. I do think its safe to say the 99-03 trucks get more out of the 42lb injectors than the 04+ models.

 

 

Richard