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 kept my fuel pressure constant and that helped knock 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 about the airflow.

 

I'm not sold on the MSD voltage booster mine killed 3 stock fuel pump,so I went with a inline pump,then I went with a bigger inline pump a Edelbrock XS that is rated for about 1000hp and I'm running 57lb injectors.

 

Thanks for the info, Whitt. This one I have is triggered by a pressure switch that kicks it on at 3 psi boost. I would expect to not have any issues because I'm not in boost above 3 psi very long or very often. How do the 57's idle?

 

The 57s idle fine you just have to scale the injectors.

 

Good right up Cory...

Injectors are not magic, they can only supply so much fuel vs pressure. I would look at the 57's. You might have a small pulse width at idle though...


Jimbob

 

What I've just recently read from Big Tex makes me think that my setup might be a little less "outside the parameters" of the 42 lb injectors if I had a 03 truck because of the way the 03 system applys a bit more fuel pressure as vacuum drops. Even if I had a 03 I'd still be at or over the (most likely over) the 20 ms at 6000 rpm rule.

Again... just goes to show that blanket statements are worthless. There are many variables to consider before saying 42's are or are not big enough.

 

Thats an awesome right up. I need to spend some time with HPTuners as I have no idea how to log injector times. Is that the same as duty cycle?

 

You can look at the injector "on" time right there in the scanning software graph from hpt. If you pause the saved log run you can move the cursor across the display and it will tell you what it happening where in relation to rpm. It's a great suite and well worth the expense.

 

DANG it Cory!! I hate being right

anyways it looks like new injectors are in your future Looks like the 57Lph (48@3bar?) is what you need

Good luck and great work!

 

Hmm... looks like this thread has been left for dead by my fellow Radix faithful. It's not the end of the world or anything bad about the Radix. It just needs bigger injectors at a certain point on some applications... Like mine.