Vaporworx / Rick's Tank Problem - dropping fuel pressure at high rpm?
 

Tonight while running through some datalogs from my tuning runs this afternoon I noticed something strange. My fuel pressure at the fuel rails is dropping at mid-to-high RPM. I did not expect to see that, so I'm wondering if this would be considered 'normal' or not.

I have a Rick's Tank with the Vaporworx setup, with the (I think) 5th Gen fuel pump / regulator as purchased from Rick's. I'm running a combination of -6AN and 3/8" hardline from the tank to my fuel rails, and my pressure sensor is at the dead-head end of the rail. I'm running a set of 39 lb/hr injectors on the engine.

You can see in the plot below that the AFR as measured is pretty stable, so perhaps my ECU has already 'tuned in' the drop in pressure. But I was surprised to see a 6# drop.

Has anyone else noticed this with the same pump / tank setup? Anyone else surprised by this?

BTW, I only noticed this because, of all things, my ignition timing dropped way down at this time, and I couldn't figure out why. I then realized that the Holley HP EFI setup I have was pulling timing (as I have it set up to do) when the fuel pressure dropped below 53psi. So at least I 'tested' out that functionality... ;)

http://i100.photobucket.com/albums/m...ps8b78fc9c.gif

I am running the same Vaporworx system on my car, other than I have the CTS-V fuel pump rated at 380lph. I also have a 6AN line running from the fuel tank to the fuel rails. I am running my system pressure at 58psi and it never varies more than a couple of psi from idle up to peak rpm. My Vaporworx pressure sensor is mounted in-line very close to the fuel tank. I measured the system pressure at the fuel rail with a mechanical gauge.

I know the 5th generation Camaro LS3 fuel module is rated at 255lph, so depending on your HP level maybe you need more capacity on the pump? I don't think it's normal to drop 6psi, mine stays very consistant at 58psi.

Thanx for the feedback. This engine was dynoed at 615HP when built, but since I'm still tuning, I don't think I'm up in that range at this point.

And the strange thing to me is that it starts losing pressure at lower RPM. I'm down 2PSI at 3500 RPM when I did the 1-2 shift, and 3PSI at 4000.

I'm going to need someone with more engineering knowledge about the flow requirements than I have off-hand to help determine if I need a bigger pump. ;) I'll try to Google it later, but I would be surprised if I'm losing pressure due to lack of flow that early in the engine speed scale.

I'll see if I can add the injector flow rate to the chart. Maybe that will signal something to me as well...

Just for reference... I tested the Vaporworx digital controller and fuel pump when I ran my engine on the engine dyno. My engine put out 672HP @ 6,900 rpm... I measured the fuel pressure and voltage output of the controller. At 1,200 rpm the fuel pump digital controller measured about 7 volts to the fuel pump, and at 7,200 rpm the controller measured between 11 to 12 volts to the fuel pump. I had plenty of capacity to support my engine with the 380lph pump... but I don't think the the 255lph Camaro pump would have been enough.

My fuel pressure does drop slightly for an instant when you first hit it but no more than 1 or 2 psi at any time.

So I tested a bit more this afternoon, and I saw a full throttle run where I dropped to 45 psi! That's no good...

I discovered that the Holley HP EFI will actually give me a Fuel Flow calculation as one of the pieces of data in the Datalog. If the number is to be believed, then it showed a max value of 299.2 lb/hr. If your 5th Gen pump number of 255 lb/hr is right, and my Holley number is right, then I'm out of fuel pump. :(

That would seemingly make sense, but it's also a bit surprising to me. I need to go back and reread the Vaporworx threads, but I thought the 5th Gen pump was the recommended setup. Maybe it's only good up to about 500HP or so?

Bryan - like Dale I've got the CTSV pump. I believe the 5th gen is maxed out at 600hp, and in the real world maybe a little less. IIRC, my injectors were spec'd a little larger than yours as well.

Get in touch with Carl and he'll get you straight.

Bryan, If you are still testing today try this... measure the voltage output of the digital controller (12V positive output to the fuel pump) and if it measures 12 volts before you get to peak rpm then you know the fuel pump is not large enough. From my understanding... the digital controller increases the voltage to the fuel pump as the demand for fuel goes up- to maintain the desired fuel pressure. If you measure 12V output at the controller before peak rpm then your out of pump capacity.

Carl helped me to size my fuel pump and I believe that he said when you get around 600HP then you need the CTS-V pump like Ron said. Carl is a great resource for help. Also.. the capacity on the 5th gen pump was 255 liter per hour rather than lb/hr.

For some reason I keep thinking that the fifth gen pump should be able to handle your amount of power. When I spoke with Carl I remember debating which pump to run and choosing the CTSV because because the fifth gen pump wouldn't be able to support the engine if I got above 650-680ish. I think that is where it maxes out on n/a engines. Gregg B is running a fifth gen pump to its limit and has around 560rwhp. He hasn't mentioned a drop in pressure at high rpm and he is pretty careful about getting everything right.

I had a similar conversation with Carl about the max horsepower limits the 5th gen module could handle and he said he had a customer using one on a motor with 630hp. I hope Carl chimes in soon as I am contemplating some mods and would like to know the limits of the 5th gen module.

I'm actually not using the Digital Controller, I'm just using the Gen 5 pump assembly and its controlled by the HP EFI. So it's either on or off, I'm not using the PWM controller.

I've been re-reading the Vaporworx threads, and I think I'm going to order one of the controllers. But I don't know that it will solve my problem, since I'm running it full blast already.

I captured some more data last night that I need to process, I'll try to post up another screenshot later.

Hmm, I need to do a conversion then to see how the liter/hour converts to the lb/hr value. It sounds like I'm on the edge of what the 5th Gen pump can handle though, although I would think that given that I'm not really fully tuned yet, I wouldn't think I'm running full fuel. Perhaps I have it set a touch too rich, and maybe leaning it out will help, but if I'm that close, then it's a problem it sounds like...