Hey all, I am looking for pictures of the cam setup in our head. If anyone has had the valve cover off, and happen to have a pic, please post up.

I am just wondering how our cam driven high pressure fuel pump works. Does it use a rocker arm, a tappet, or what?

 

if my engine is still taken apart at the shop i will post pics of the head monday

 

Sounds good. I am focusing on the part of the cam that runs the fuel pump, so if you can get some good pics of that, I would appreciate it!

 

ok cool i might go up to the shop today or monday im sure the engine is still apart i will let you know though by mon

 

what did you do to your car?

 

i have some pics of head but you are going to have to go to the dungeon to see them haha

 

Here are two pics from when Sukxost had his valve cover off. Saved them so I could study them too.

 

I have some gimme a sec

 

Hmm, I need some more that are aimed into the fuel pump. I am just trying to figure out if that's how ZZP raised their fuel pressure. It has me stumped.

 

I've got two theories so far:

1) They raised the voltage on the fuel tank fuel pump, so it pumps more fuel.
2) They're using a "piggyback" fuel injector setup, allowing them to use conventional, non-DI injectors that they can use to do whatever they want after the DI system is "maxed" in the ECU.

Edit: I read their original thread again, and I withdraw option 2. Although it would work, the way they phrased the mod ("pressure modifier") makes option 2 seem less likely. If the pump is on a geared system of some sort, then it'd be very easy to do... just change the ratio between the gears.

 

or zzp has a version of hptuners that we don't have yet..

 

Yeah, I think #1 is the most likely possibility, without going to something mechanical, but I think we have a pressure regulator, so that would not work if we do. I might have to give this a try.

#2 is out, for the main reason that he said his fuel pressure was around 3k psi or something.

I might have to play with the pump voltage. I think if I hooked a WOT switch up to a power source, and hooked that to the tank pump to up the voltage then it would only give more pressure at WOT.

But, then again I don't think the tank pump has anything to do with it, since I see no way for it to up the pressure to nearly 3k psi, if not over.

This COULD be possible as well because HPT has been looking for big turbo LNF's to test the fuel pressure on. But, I slightly recall Matt saying it would be somehting they would be releasing.

 

ZZP sells fuel pump rewiring kits, so it'd be very feasible for them to do that in this case. Flow may still be limited due to the mechanical nature of a cam driven fuel pump, but I was just coming from the fact that the more pressure you pump to the cam fuel pump, the less hard it would have to pump.

Keep in mind the different natures of the pumps. The fuel tank pump is a low-pressure, high volume pump, where the cam fuel pump is meant to basically take the same volume and simply bump up the pressure to that needed to make DI work. The fuel tank fuel pump doesn't need to have high pressure, it just needs to flow enough fuel to feed the cam driven fuel pump.

Maybe the secret is in how the regulator works... hmmm...

 

Yes and no, I think... yes the tank pump is high volume, but I don't think that you could bump the pressure up enough from that to affect the cam pump by any major means. ZZP said they were around 3k, IIRC. This is up from a max of 2200. I just don't see the tank pump giving us 800 psi boost. So, we would have to speed up the cam driven pump, or change the ratio of pump/cam.

Again, I am very unfamiliar as to how this works, so I am speculating right now.

 

don't know if these help

 

Speculation here too.

Yeah, like I was saying about the mechanical part of the cam driven pump, it may only pump what it pumps no matter the input pressure. I'm not familiar enough either with how it works.

I'm with you on your final point. After thinking about it and talking with you, I'm leaning more towards a pump/cam ratio tweak too.

 

Not a ton... but that first one is nice and clear. I need to break into the pump, and see if there is a way to modify it. I could be rich if I figured it out, lol.

The GOOD thing is that the shop I work for has hit 414 on a solstice (more drivetrain loss) so that would be about 440whp on a balt (on race gas though), and I think that will suffice for the majority of the population of Balts.

Yeah, I am wondering if we couldn't break into it, and just add a very small tappet. ZZP said they did not open the pump up and change internals though...

 

Who cares what they did if there's an even better solution.

I'm having trouble finding pics of LNF cams, but here's a cam off a jeep:



Yeah, it seems random, but I read that the cams on them are used for both fuel and oil pumps and use eccentric gears to do the pumping. I wonder if the LNF intake camshaft end is similar. The screws/gears inside the pump could be machined or matched to flow more fuel too in addition to the cam-to-pump gearing idea.

 

Hmmmm... theoretically it could. I just wish HPT would hurry up. I got a shop wanting to make some more money, and do a nasty build on some Solstices!

 

Found a pic of the inside of a cam driven fuel pump.

Bottom right of this pic... this may be like what we're dealing with...



Fuel comes in one side, passes between the gears and is trapped on the other side after that. Constant rotation of the gears creates a flow.

Man, I need to go back through my old fluid and mechanical power transmission books now.

Being that our fuel system is a returnless system, I'd say that the pump is a positive displacement pump, so that helps us narrow it down.

Something that's interesting to note too is after turning off the engine, the RPD will read a steady and/or slightly increasing fuel pressure for quite some time. If you come back the next morning or sometime later and boot the RPD without starting the engine then it'll be showing only a double digit fuel pressure in the fuel rail. Where did the fuel/pressure go? It can't go back into the gas tank if it's a returnless system with a check valve in the line too. It's a mystery...

 

That setup is a spur gear pump being used for oil pressure, not for fuel and would also not work very well (or at all) for the types of pressure needed for direct injection. And if you're curious what the Bosch high-pressure mechanical pump used on the LNF looks like, below are some pics from GM Media showing fuel system components.

LNF valvetrain

DI high-pressure pump, head side

DI high-pressure pump, external side

LNF piston and injector geometry

LNF fuel injector, top

LNF fuel injector, tip

LNF fuel rail w/injectors


If you look carefully at the first picture you can see the lobe on the end of the camshaft in the housing that drives the mechanical pump. Since the pump is pretty well sealed and non-serviceable, you could possibly alter the lobe and/or tappet of the pump, but my guess is that since their is some sort of internal solenoid that controls how much of the fuel is bypassed in order to control pressure, the easiest method would be for the computer to command increased rail pressure up to the limits of what it can flow.

Speaking of fueling and since I haven't been following it as much in the last few months and haven't played around with HP Tuners yet, for direct injection you have a window near the top of the piston's travel at top dead center when the compression stroke peaks and the fuel is injected just prior to ignition. Have they looked into injecting elsewhere in the compression stroke or does the HP Tuners software not address that capability yet?

The Bosch ECU used on the LNF cars already does split-injection when the car is initially started to help aid in catalytic converter light off. Besides injecting at the compression peak it also double-fires the injectors a second time early in the intake stroke. This is the fast paced ticking you hear prior to the ECU switching over the slower tick as it warms up. The question would be is that since you have less and less time for the injectors to be open as rpms increase, are the injectors being commanded open the entire intake and compression stroke, and if not, is that something HPT will be able to support.

Doing so would essentially give you the equivalent of a port-based fuel injection system (just that its not firing into the intake port but still into the combustion chamber) as well as being able to inject up to the peak of cylinder pressures. Now if the injector duty cycle is already commanding them open during the intake and compression stroke the only way to get more fuel would be to increase fuel pressure (so more gets out in the same amount of time they're firing/open) or to upgrade the high-pressure injector to unit that flow more at the same pressure (assuming the high-pressure pump can sustain the flow volume and wouldn't drop pressure with the bigger injectors).

 

He's been kinda quiet lately, but on another site called lnfperformance a GMPP engineer talked about the fueling issues. Essentially he said forget about injector duty cycle, your issue is raising the pressure ala diesel. He also eluded that HPT could accomplish that, and also gave some ballpark pressure limits to the system.

It was your thread even mkriebs

www lnfperformance com/forums/showthread.php?t=868

Depending on ones power goals... the solution isnt mechanical. The solution lies within the PCM and we need to keep pressure on HPT, no pun intended. I also think ZZP's recent posting gives good credibility to that notion.

 

There's a few places that make aftermarket high pressure fuel pumps for MS3's. As I said when these motors first came to Cobalt's, I said someone should contact them. It wouldn't be hard to modify the pump.

If you have some electrical experience, I'm sure you could trick the solenoid into doing what you want.

 

Yeah, I remember that thread. I just was trying to figure out a second solution, since HPT seems to be dragging their feet horribly.

 

Wow! Thanks Blackbird!

The pics help to see what we're dealing with better too.