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

[Matt@BOS]

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.

[rocketrod]

Originally Posted by Matt.A

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.

[carbuff]

Originally Posted by Matt.A

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 feel like it should handle it also. It's strange to me that I start seeing the pressure drop at lower RPM, where I'm certainly not making that kind of power. I checked the battery level (via the Datalog) during the run, and there wasn't a drop in voltage, so that wasn't the problem either...

[Matt@BOS]

How close to the battery did you mount the controller? I'm wondering if there might be something not working properly between the battery/controller/pump.

[carbuff]

Matt,

The ECU is mounted on the cowl in the cab, if that's what you were asking. I don't have the Vaporworx PWM controller (yet).

If the conversion factors that I'm finding for lb/hr to l/m are correct, then at 300 lb/hr (which my ECU reports), that should be 3.15 lpm. Multiplied by 60 m/h, that should only be 189 lph. So I should be within the limits of the 5th gen pump. Unless my math is wrong, and obviously I'm just relying on the ECU data.

[CarlC]

Sorry guys, I'm just finding this one.

The PWM controller won't increase output. It slows down the pump to decrease the amount of heat generated and to reduce wear. The only thing that is going to increase pump performance is to increase the input voltage.

The Gen5 LS3 pump was used on James Shipka's OLC with the Katech LS7 was a nice match for that setup. It made about 630hp. The pump had a small safety margin in that car but it supplies 14 volts at the controller input. That helps pump performance. Engine efficiencies and input voltages can make a big difference here as well since it's getting close to the maximum output of the pump.

It is normal that pressure will drop in a non-manifold referenced system during part throttle. The C5 Corvette fuel filter/regulator does the same thing and has very similar output curves. As more fuel flows to the engine, the pressure drop will increase to the point where no more fuel is bypassed by the regulator. There is another pressure regulator available that does not have as much pressure reduction, Delphi FP10075. It does have a slightly higher it-idle pressure of 61-62psi but will only lose about 3psi at full bypass.

Three things come to mind here:

One, the fuel pressure regulator may be partially dislodged and causing an internal leak. To check for this fuel module removal is required.

Two, there may be a restriction in the fuel line. To check for this a fuel pressure gauge would need to be placed near the fuel module outlet and compared to the pressure at the injector inlet. A small difference will be normal as there are losses due to friction and fitting restrictions.

Three, the pump may be too small. At 50psi the regulator should be sending all of the fuel to the engine. At 50psi/13.5v the pump can supply 326 #/hr, enough to feed a naturally aspirated engine to 652 horsepower at a conservative 0.5bsfc with an appropriate injector. However, there's not much safety margin.

Some numbers:

At 13.5v:

60psi = 300#/hr or 189 liters/hr
55psi = 313 197
50psi = 326 206
45psi = 339 214
40psi = 353 223

For naturally aspirated engines the brake specific fuel consumption (bsfc) is considered to be 1/2# per hour of fuel for each horsepower. So, at 50psi the pump can provide 326#/hr. Divide this by 0.5 (1/2). That results in 652hp. However, there's no safety margin.

You may also want to check here for some injector calculations http://www.rceng.com/technical.aspx

For 650hp, 80% injector duty cycle, and 58psi fuel pressure a 44 lb/hr injector would be a good choice. It sounds like you may already be at the limits of your current injector as well, but the fuel pressure side of things should be fixed first.

Injectors are typically rated for 43psi (3bar), not 58psi (4bar). I won't go into the gory details of all this unless you want me to, but it's a good practice for us. So, at 42psi you're looking at a 52 lb/hr injector (assuming eight injectors.)

You may also want to check that the wire gauge to the relay(s) is 14ga minimum and that there is not a large voltage drop to the relay output. The Gen5 LS3 pump needs 12 amps.

If it is determined that the fuel pump needs to go bigger the easiest thing to do would be to put in a ZL1 fuel module. You can test this by putting in the fuel module using the 58psi regulator that is in your current fuel module. Though not recommended for extended use, it will work to get the system figured out. The ZL1 is capable of:

60psi = 391#/hr = 247 l/hr
55psi = 415 262
50psi = 436 275

It also needs 17 amps, so a PWM system is recommended for this setup for long-term use.

[carbuff]

Carl,

Thank you for responding with so much information! Of all of the suggestions that you have provided, I think the following may be the one I need to focus on:

Originally Posted by CarlC

You may also want to check that the wire gauge to the relay(s) is 14ga minimum and that there is not a large voltage drop to the relay output. The Gen5 LS3 pump needs 12 amps.

I'm using the 'relay' from the Holley HP EFI kit, which supposedly will source 10A. I do have 12 or 14ga wire, I don't recall which at the moment. I unfortunately do not have a good way to measure the actual voltage at the pump itself, but if it requires 12A, then it's very possible that I have a limitation on the available current. I did not run an extra relay for the pump itself, since I was under the impression that the HP EFI could source it. That may be my mistake.

If I'm going to dig back into this wiring, then it may be a good time for me to go ahead and install your PWM controller instead of just a relay. I don't think it was available when I made this original purchase, which is why I don't have one now...

I will contact you via PM about acquiring one...

Thanx again!

[CarlC]

I'm glad to help Bryan.

If you want to to a check of the wiring remove the circuit that connects the relay to the fuel pump. Take the output from the relay and run it to BAT + (assuming it's +). Do the same for the negative, or confirm that the chassis ground is secure and has direct contact with the chassis material, i.e. no paint, corrosion, etc. It won't hurt the pump to connect it like this with the engine not running. Connect everything with the engine off, then try running the car again. Use an in-line fuse to protect the circuit. The circuit should be capable of 20A in either case.

In the end you may well find out that the LS3 pump is a bit small for the build. The ZL1 has almost identical form, fit, and function to the LS3, the only difference being that the ZL1 won't compress quite as much as the LS3 due to the taller pump in the module reservoir. This is only a factor if you have retro-fitted an older Rick's, Rock Valley, or stock tank since these are only 7" tall overall. All of the tanks fabricated by Rick's or RV have sufficient mouting height to accomodate either fuel module.

The basics of the PWM kits will interchange among the LS3, ZL1, an CTS-V single fuel modules. The LS3 and ZL1 kits are identical. The CTS-V has a different short harness since the wiring for the plug on the fuel module hat is different. In other words, if you have a PWM kit for an LS3 and want to use a ZL1, just put the new pump in and go. When running twin fuel modules, like that in Mark Stielow's latest builds, it requires a different controller tune to get the system happy when running both pumps at the sam time, plus there is a lot more wiring to tie in the second module.

[LowFlyin']

Originally Posted by carbuff

I'm using the 'relay' from the Holley HP EFI kit, which supposedly will source 10A. I do have 12 or 14ga wire, I don't recall which at the moment. I unfortunately do not have a good way to measure the actual voltage at the pump itself, but if it requires 12A, then it's very possible that I have a limitation on the available current. I did not run an extra relay for the pump itself, since I was under the impression that the HP EFI could source it. That may be my mistake.

If I'm going to dig back into this wiring, then it may be a good time for me to go ahead and install your PWM controller instead of just a relay. I don't think it was available when I made this original purchase, which is why I don't have one now...

I will contact you via PM about acquiring one...

Thanx again!

Hey carbuff, I was directed to this thread by a community member, I work for a fuel pump and injector manufacturer and was actually in the process of flow testing the stock LS3 pump from the 5th Gen Camaro.

From 30psi up to 100psi, it was using 10.6-15.2 amps @ 13.5 volts. If I'm reading your first sentence right, you are over extending the Holley EFI relay.

From the looks of it, the pumps is actually quite good. My numbers are showing for 675hp at the crank you'll need around 195LPH of fuel from the pump. At 60psi, the LS3 pump was putting out 220LPH by our testing equipment.

As Carl pointed out, you'll need around at least 45# injectors to keep the IDC's in the 80's with 675hp...and also a 44# injector at 58 psi will yield ~52#.

If your current injectors are essentially going static, I could see that being a source of your fuel pressure drop, as well.